OBSERVING PLAN

          The Philippine Astronomical Society and the Astronomical League of the Philippines often organize out of town overnight observing sessions. They bring along their telescopes and other equipment, and sometimes even their swimming attire and fishing rods. Just ask them if you like to join. They will never deny your request. Even if you do not have your own telescope they will allow you to view through theirs, if they are not doing astrophotography or engaged in a systematic study. You will be given instructions about what to bring, such as Off lotion, snacks, jackets, drinks, hat, anything that would make observing comfortable. Bringing liquor is not allowed, as far as I know. Do not observe while drinking beer or any alcoholic drinks. They make single stars look double!

          Oftentimes, however, there are surprises in astronomy. On many occasions, I studied the sky charts and observing guides from Astronomy and Sky and Telescope magazines the whole day and got ready physically and mentally for a night of observing delightful deep-sky targets when clouds began to gather in late afternoon. The sky would then be cloudy and that’s it for observing that day. One time I set up the telescopes in the hope that the cloudy sky would clear. After an hour of waiting the sky wouldn’t clear so I would just bring the telescope back inside the office and then go home. And then the sky suddenly cleared… Or you might think it would rain tonight, and then the sky would be very transparent and pristine.

          I suggest you make an observing list of objects you wish to see. Most astronomers who use telescopes would like to complete their collection of Messier objects. Some observe only globular clusters or galaxies. In the beginning you will be a more general observer, sampling the delights of the heavens like you’re in a smorgasbord, but later your interests will concentrate on select objects.

          There are a lot of things to do in astronomy that will make your observing useful, but do not rush into trying to do useful work right away: it would take time. But even if you observe in the city, you can follow and make light curve charts of variable stars, or see the patterns of where the Sun rises and sets in particular times of the year.

          You must have an observing diary. Write there the descriptions, or even sketches of the objects you have observed. Take careful note of the sky condition, your location, the time of observation, and the equipment used.

          Just keep on observing. Your efforts, even in your tiny way, will contribute to mankind’s knowledge in astronomy and science.

                                                                     BINOCULARS

           Binocular observing is a both a pleasurable and scientific pursuit in astronomy. I started looking at the night sky with a 7 x 35 Bushnell binoculars I bought from Hahn Manila in Megamall. I was sweeping the then pristine sky in Montevista Heights in Taytay, Rizal with this instrument without really knowing much about what I was looking at. I have seen the Double Cluster in Perseus and the Great Orion Nebula but I did know then what these magnificent objects were all about. Later, when I was reading all the books about Astronomy, and even Physics, I could lay my hands on, I learned that knowledge is the greatest equipment for the astronomer. With knowledge, the sky comes alive. Without it, those objects we see are really almost meaningless.

          The “7” in 7 x 35 means that this pair of binoculars magnifies the view by 7 times. The “35” is the aperture of the light-collecting lenses of the pair, called the objective lenses. The general rule is the bigger the objective lenses, the binoculars would see fainter objects. So, a pair of 7 x 50 binoculars would be able to see fainter objects than a 7 x 35. However, I think the quality of the binoculars is also important in seeing the fainter objects. I had three 10 x 50 pairs, one a Simmons, the other a Tasco, and the last one is my favorite Pentax. The Pentax shows objects much, much better than the other pairs. I have a Russian-made 7 x 40 given to me by an old colleague who has since transferred to another school, but the Bushnell 7 x 35 shows brighter images than the 7 x 40.

          There are higher magnification binoculars. You can buy 12 x 50, 16 x 50 and even 20 x 50 pairs in department stores but I do not advise that you buy them even if you can afford them. They are hard to hold steady, and the images are not as good as in the 10 x 50 or 7 x 50. Besides, I am not very sure about the quality.

          Avoid those camouflaged binoculars vendors sell on the sidewalk. They are good only for looking at pretty neighbors or quarreling spouses across the street. Avoid also those small binoculars with red-coated objectives. They are not good for astronomy.

          If you will buy a pair, I suggest you ask a member of the Philippine Astronomical Society or the Astronomical League of the Philippines to accompany you. Some binoculars being sold are out of alignment. You can detect this if you look at a distant object and immediately remove your eyes from the eyepiece. If you can see merging double images, it means the binoculars are out of alignment. It must have dropped. This is also one reason why you should not ask relatives to bring home binoculars for you. They may not know if the binoculars are properly aligned or not.

          Never ask sales ladies in department stores to tell you anything about binoculars. Chances are they don’t know anything about them.

          Do not drop your binoculars. Always use the neck strap. When someone would like to use your binoculars always put the strap around their necks, so when he drops the binoculars, it wont drop! And tell them not to touch the objective lenses. They are very hard to clean and requires special skills!

          Good binoculars available here are Nikon, Pentax, Minolta, and Bushnell. We are told that Bushnell binoculars are being manufactured in Cebu City, and before the brand name is put in the item, it costs very cheap. Watch out for sales.

                                                                                     TELESCOPES

          Most of my early observations were done using my 102-mm or 4-inch, Celestron achromatic refractor. I like its ease of use since it is an altazimuth mount, which means that you can just swivel the telescope up and down and sideways. The telescope is equipped with two kinds of finders, the red-dot finder for pointing the telescope in the approximate location of the target, and the visual finderscope for tracing star patterns near the object. We call this last process star-hopping. The finderscope is a low power, wide field, small refracting telescope. Before I used the standard 6 x 30 finderscope supplied with the telescope when I bought it, but now I use the 9 x 50 finderscope supplied in my Orion XT-10 Newtonian reflector, though this configuration sometimes causes balancing problems in the altazimuth mount when the telescope is pointed very high in the sky. The images in the refractor are sharp, especially when I use the good Celestron Plossl eyepieces I have. Double stars and many bright and relatively bright open clusters are well-defined and resolved. However, the telescope has limited uses especially for nebulae and galaxies since it has limited aperture and since I observe in the light-polluted urban area and there is a significant amount of color around bright objects such as Venus. They call it chromatic aberration.

          Most of my observations of deep-sky objects were done with the 200-mm or 8-inch Celestron Schmidt-Cassegrain telescope (SCT). I seldom use its equatorial wedge. I just put the telescope in a platform or improvised heavy-duty tripod manufactured in the RTU. This telescope has a 9 x 50 finder and a Telrad bulls-eye finder. I have an 80-mm Lumicon finder I use when observing galaxies. I had a very heavy table on the RTU Pasig Campus roof deck when that campus still had a roof deck. I find this arrangement very ideal for visual observations. The SCT provides images of pale and dim objects such as galaxies and nebulae, but the star images are not so sharp compared to the refractor though there is no chromatic aberration. One problem I’ve had with the SCT is that it sometimes go out of collimation, meaning its optics tend to get disarranged. Without a motor drive, it would take about an hour of precious observing time to get the collimation in order.

          Many of my deep-sky observations were done with my 250-mm or 10-inch Newtonian reflector on Dobsonian mount. The telescope is easy to set up and use. It is supplied with a 9 x 50 finder scope and a Telrad bulls-eye finder. I have made some very detailed sketches of Mars during its nearest approach to Earth in 2003. I have seen so many galaxies I could not detect with the 8-inch. My only concern with this telescope is its weight.

          My champion, and the telescope I use most often when showing the students, and even the neighbors, the heavens, is the 4.25-inch or 105-mm Astroscan telescope. It is a unique telescope (see the review I downloaded from the Internet). I can carry it everywhere I go. It has seen starlight in Boracay and Puerto Galera where beach goers lined up for a look at the planets during the planetary alignment in May, 2002. It has seen a lot of deep-sky objects, including many dim globular clusters in the Messier Catalog. “Nice baby!”, Mr. Prasad Agrahar, astronomer from India, remarked when I arrived carrying the instrument in one observation we conducted at the Manila Observatory in Ateneo De Manila University.

                                                                                        Refractor Telescopes                                               

          The refractor telescope uses a lens to gather and focus light. The first telescopes built were refractors. The small telescopes sold in department stores are refractors, as well as, those used for riflescopes.

Advantages   

• Refractor telescopes are rugged. After the initial alignment, their optical system is more resistant to misalignment than the reflector telescopes.
• The glass surface inside the tube is sealed from the atmosphere so it rarely needs cleaning.
• Since the tube is closed off from the outside, air currents and effects due to changing temperatures are eliminated. This means that the images are steadier and sharper than those from a reflector telescope of the same size.

 

          Though excellent refractors are still made, the disadvantages of the refractor telescope have blocked the construction of very large refractors for use in astronomical research.

Disadvantages

1. All refractors suffer from an effect called chromatic aberration (``color deviation or distortion'') that produces a rainbow of colors around the image. Because of the wave nature of light, the longer wavelength light (redder colors) is bent less than the shorter wavelength light (bluer colors) as it passes through the lens. This is used in prisms to produce pretty rainbows, but can it ruin an image!

There a couple of ways to reduce chromatic aberration. One way uses multiple compensating lenses to counteract chromatic aberration. The other way uses a very long objective focal length (distance between the focus and the objective) to minimize the effect. This is why the early refracting telescopes were made very long.

1. How well the light passes through the lens varies with the wavelength of the light. Ultraviolet light does not pass through the lens at all.
2. How well the light passes through decreases as the thickness of the lens increases.
3. It is difficult to make a glass lens with no imperfections inside the lens and with a perfect curvature on both sides of the lens.
4. The objective lens can be supported only at the ends. The glass lens will sag under its own weight.
   
   http://www.astronomynotes.com/telescop/s2.htm, http://www.fyeo.com/contents/products/bushnell-570x60-refractor.html
   
   
   
   

   Reflector Telescopes      The reflector telescope uses a mirror to gather and focus light. All celestial objects (including those in our solar system) are so far away that all of the light rays coming from them reach the Earth as parallel rays. Because the light rays are parallel to each other, the reflector telescope's mirror has a parabolic shape. The parabolic-shaped mirror focuses the parallel lights rays to a single point. All modern research telescopes and large amateur ones are of the reflector type because of its advantages over the refractor telescope . Advantages Reflector telescopes do not suffer from chromatic aberration because all wavelengths will reflect off the mirror in the same way. Support for the objective mirror is all along the back side so they can be made very BIG! Reflector telescopes are cheaper to make than refractors of the same size. Because light is reflecting off the objective, rather than passing through it, only one side of the reflector telescope's objective needs to be perfect.

   
   
   Disadvantages
   1. It is easy to get the optics out of alignment.
   2. A reflector telescope's tube is open to the outside and the optics need frequent cleaning.
   3. Often a secondary mirror is used to redirect the light into a more convenient viewing spot. The secondary mirror and its supports can produce diffraction effects: bright objects have spikes (the ``christmas star
      effect'').
      http://www.astronomynotes.com/telescop/s3.htm
      
      

      Schmidt-Cassegrain Telescopes Celestron has long been recognized as a leader in Schmidt-Cassegrain technology. Our line of Schmidt-Cassegrain telescopes ranges from the highly portable C5+ all the way up to the powerful CG-14, and includes several cutting edge computerized telescopes. Celestron's potent combination of superior optics, fine drive systems and well-crafted mechanics puts these telescopes in a class by themselves. Schmidt-Cassegrain, or catadioptric, telescopes use a combination of mirrors and lenses to fold the optics and form an image. Incoming light enters through a thin aspheric Schmidt correcting lens, then strikes the spherical primary mirror and is reflected back up the tube. The light is then intercepted by a small secondary mirror which reflects the light out an opening in the rear of the instrument, where the image is formed at the eyepiece.

      
      

      Some of the advantages of the Schmidt-Cassegrain design are: Excellent optical systems delivering razor sharp images over a wide field. High performance in almost all situations; terrestrial viewing and photography; lunar, planetary and deep-sky observing; astrophotography with fast film; CCD imaging. Best all-around, multifunction telescope design; it combines all the optical advantages of both mirrors and lenses, while canceling their disadvantages. Focal ratios generally in the range of f/10, which is useful for all types of photography. A telescope that's compact, portable, easy to use, durable, virtually maintenance free and has a closed tube. The best near focus capability of any type of telescope design. Large apertures at quite reasonable prices. Many accessories available.

      http://www.catsanddogspa.com/schmidt.html, http://www.binoculars.com/products/celestron-8-inch-cpc-schmidt-cassegrain-32982.html
      

                                                             THE MESSIER CATALOG
      
         The very first list of objects an amateur astronomer would wish to complete observing is the Messier Catalog. At a glance, the Messier Catalog is a list of 110 (some astronomers limit the number to 109) objects.
      
         After Galileo Galilei applied the telescope for astronomical purposes, astronomy in the 18 th century exploded with discovery. The telescope opened up hitherto unknown aspects of the heavens. The telescope revealed hundreds of previously unseen objects. It fell to the astronomers to catalog all these objects so that they will be able to routinely find and study them.
      
         The French astronomer Charles Messier (1730-1817) began to catalog objects in the sky which look like comets but are not, so he would not be confused by them. It is said that Messier’s real passion was to look for comets, but he was fooled by a nebulous object which he though was a comet but never moved with respect to the stars. He called similar objects “embarrassing objects.”
      
         The result of his cataloging efforts is a list of the sky’s “greatest hits”. In observing sessions of the astronomical societies in the Philippines, all reports of the sessions would enumerate the Messier objects observed during the night. Peter Benedict Tubalinal, a long-time amateur astronomer, has been initiating Messier Marathons for years now where participants would try to see all Messier objects in one night. Peter achieved a perfect 110 record just recently. Stephen Maran in his book Astronomy for Dummies , however, gives an advice: “But in a marathon, you have no time to enjoy an individual nebula, star cluster, or galaxy. I say: ‘Take it slow’ and savor their individual visual delights.”
      
         The instructor should schedule a night of observing (but not necessarily for the whole night!) and you should try to see as many Messier objects that would be visible during the time you observe. Bring a personal log where you can record your observations and impressions, or a sketch pad so you can sketch what you see.
      
      

      THE MESSIER CATALOG

      Messier number

      NGC number

      Common name

      Object type

      Distance to object in thousands of light years

      Constellation

      Apparent magnitude

      M1

      NGC 1952 The Crab nebula

      Crab Nebula

      Supernova remnant

      6.3

      Taurus

      9.0

      M2

      NGC 7089

      Globular cluster

      36

      Aquarius

      7.5

      M3

      NGC 5272

      Globular cluster

      31

      Canes Venatici

      7.0

      M4

      NGC 6121

      Globular cluster

      7

      Scorpius

      7.5

      M5

      NGC 5904

      Globular cluster

      23

      Serpens

      7.0

      M6

      NGC 6405

      Butterfly Cluster

      Open cluster

      2

      Scorpius

      4.5

      M7

      NGC 6475

      Ptolemy's Cluster

      Open cluster

      1

      Scorpius

      3.5

      M8

      NGC 6523

      Lagoon Nebula

      Cluster with nebula

      6.5

      Sagittarius

      5.0

      M9

      NGC 6333

      Globular cluster

      26

      Ophiuchus

      9.0

      M10

      NGC 6254

      Globular cluster

      13

      Ophiuchus

      7.5

      Messier number	NGC number	Common name	Object type	Distance to object in thousands of light years	Constellation	Apparent magnitude
      M11	NGC 6705	Wild Duck Cluster	Open cluster	6	Scutum	7.0
      M12	NGC 6218		Globular cluster	18	Ophiuchus	8.0
      M13	NGC 6205	Great Hercules Cluster	Globular cluster	22	Hercules	5.8
      M14	NGC 6402		Globular cluster	27	Ophiuchus	9.5
      M15	NGC 7078	Pegasus Cluster	Globular cluster	33	Pegasus	7.5
      M16	NGC 6611	Eagle Nebula	Cluster with H II region	7	Serpens	6.5
      M17	NGC 6618	Omega Nebula	Cluster with H II region	5	Sagittarius	7.0
      M18	NGC 6613		Open cluster	6	Sagittarius	8.0
      M19	NGC 6273		Globular cluster	27	Ophiuchus	8.5
      M20	NGC 6514	Trifid Nebula	Cluster with H II region	2.2	Sagittarius	5.0

      Messier number	NGC number (or IC)	Common name	Object type	Distance to object in thousands of light years	Constellation	Apparent magnitude
      M21	NGC 6531		Open cluster	3	Sagittarius	7.0
      M22	NGC 6656	Sagittarius Cluster	Globular cluster	10	Sagittarius	6.5
      M23	NGC 6494		Open cluster	4.5	Sagittarius	6.0
      M24	NGC 6603	Small Sagittarius Star Cloud	Milky Waystar cloud	10	Sagittarius	11.5
      M25	IC 4725		Open cluster	2	Sagittarius	4.9
      M26	NGC 6694		Open cluster	5	Scutum	9.5
      M27	NGC 6853	Dumbbell Nebula	Planetary nebula	1.25	Vulpecula	7.5
      M28	NGC 6626		Globular cluster	18	Sagittarius	8.5
      M29	NGC 6913		Open cluster	7.2	Cygnus	9.0
      M30	NGC 7099		Globular cluster	25	Capricornus	8.5

      Messier number	NGC number	Common name	Object type	Distance to object in thousands of light years	Constellation	Apparent magnitude
      M31	NGC 224	Andromeda Galaxy	Spiral galaxy	2500	Andromeda	3.5
      M32	NGC 221		Dwarf elliptical galaxy	2900	Andromeda	10.0
      M33	NGC 598	Triangulum Galaxy	Spiral Galaxy	2590	Triangulum	7.0
      M34	NGC 1039		Open cluster	1.4	Perseus	6.0
      M35	NGC 2168		Open cluster	2.8	Gemini	5.5
      M36	NGC 1960		Open cluster	4.1	Auriga	6.5
      M37	NGC 2099		Open cluster	4.6	Auriga	6.0
      M38	NGC 1912		Open cluster	4.2	Auriga	7.0
      M39	NGC 7092		Open cluster	0.3	Cygnus	5.5
      M40		Winnecke 4	Double star WNC4		Ursa Major	9.0

      Messier number	NGC number	Common name	Object type	Distance to object in thousands of light years	Constellation	Apparent magnitude
      M41	NGC 2287	Little Beehive	Open cluster	2.4	Canis Major	5.0
      M42	NGC 1976	Orion Nebula	H II region	1.6	Orion	5.0
      M43	NGC 1982	De Mairan's Nebula	H II region (part of Orion Nebula)	1.6	Orion	7.0
      M44	NGC 2632	Beehive Cluster	Open cluster	0.5	Cancer	4.0
      M45		Pleiades	Open cluster	0.4	Taurus	1.4
      M46	NGC 2437		Open cluster	5.4	Puppis	6.5
      M47	NGC 2422		Open cluster	1.6	Puppis	4.5
      M48	NGC 2548		Open cluster	1.5	Hydra	5.5
      M49	NGC 4472		Elliptical galaxy	60000	Virgo	10.0
      M50	NGC 2323		Open cluster	3	Monoceros	7.0

      Messier number	NGC number	Common name	Object type	Distance to object in thousands of light years	Constellation	Apparent magnitude
      M51	NGC 5194, NGC 5195	Whirlpool Galaxy	Spiral Galaxy	37000	Canes Venatici	8.0
      M52	NGC 7654		Open cluster	7	Cassiopeia	8.0
      M53	NGC 5024		Globular cluster	56	Coma Berenices	8.5
      M54	NGC 6715		Globular cluster	83	Sagittarius	8.5
      M55	NGC 6809		Globular cluster	17	Sagittarius	7.0
      M56	NGC 6779		Globular cluster	32	Lyra	9.5
      M57	NGC 6720	Ring Nebula	Planetary nebula	2.3	Lyra	9.5
      M58	NGC 4579		Barred spiral galaxy	60000	Virgo	11.0
      M59	NGC 4621		Elliptical galaxy	60000	Virgo	11.5
      M60	NGC 4649		Elliptical galaxy	60000	Virgo	10.5

      Messier number	NGC number	Common name	Object type	Distance to object in thousands of light years	Constellation	Apparent magnitude
      M61	NGC 4303		Spiral galaxy	60000	Virgo	10.5
      M62	NGC 6266		Globular cluster	22	Ophiuchus	8.0
      M63	NGC 5055	Sunflower Galaxy	Spiral galaxy	37000	Canes Venatici	8.5
      M64	NGC 4826	Black Eye Galaxy	Spiral galaxy	12000	Coma Berenices	9.0
      M65	NGC 3623		Barred spiral galaxy	35000	Leo	10.5
      M66	NGC 3627		Barred spiral galaxy	35000	Leo	10.0
      M67	NGC 2682		Open cluster	2.25	Cancer	7.5
      M68	NGC 4590		Globular cluster	32	Hydra	9.0
      M69	NGC 6637		Globular cluster	25	Sagittarius	9.0
      M70	NGC 6681		Globular cluster	28	Sagittarius	9.0

      Messier number	NGC number	Common name	Object type	Distance to object in thousands of light years	Constellation	Apparent magnitude
      M71	NGC 6838		Globular cluster	12	Sagitta	8.5
      M72	NGC 6981		Globular cluster	53	Aquarius	10.0
      M73	NGC 6994		Asterism		Aquarius	9.0
      M74	NGC 628		Spiral galaxy	35000	Pisces	10.5
      M75	NGC 6864		Globular cluster	58	Sagittarius	9.5
      M76	NGC 650, NGC 651	Little Dumbbell Nebula	Planetary nebula	3.4	Perseus	12.0
      M77	NGC 1068		Spiral galaxy	60000	Cetus	10.5
      M78	NGC 2068		Diffuse nebula	1.6	Orion	8.0
      M79	NGC 1904		Globular cluster	40	Lepus	8.5
      M80	NGC 6093		Globular cluster	27	Scorpius	8.5

      Messier number	NGC number	Common name	Object type	Distance to object in thousands of light years	Constellation	Apparent magnitude
      M81	NGC 3031	Bode's Galaxy	Spiral galaxy	11000	Ursa Major	8.5
      M82	NGC 3034	Cigar Galaxy	Barred Spiral (?)	11000	Ursa Major	9.5
      M83	NGC 5236	Southern Pinwheel Galaxy	Barred spiral galaxy	10000	Hydra	8.5
      M84	NGC 4374		Lenticular galaxy	60000	Virgo	11.0
      M85	NGC 4382		Lenticular galaxy	60000	Coma Berenices	10.5
      M86	NGC 4406		Lenticular galaxy	60000	Virgo	11.0
      M87	NGC 4486		Elliptical galaxy	60000	Virgo	11.0
      M88	NGC 4501		Spiral galaxy	60000	Coma Berenices	11.0
      M89	NGC 4552		Elliptical galaxy	60000	Virgo	11.5
      M90	NGC 4569		Spiral galaxy	60000	Virgo	11.0

      Messier number	NGC number	Common name	Object type	Distance to object in thousands of light years	Constellation	Apparent magnitude
      M91	NGC 4548		Barred spiral galaxy	60000	Coma Berenices	11.5
      M92	NGC 6341		Globular cluster	26	Hercules	7.5
      M93	NGC 2447		Open cluster	4.5	Puppis	6.5
      M94	NGC 4736		Spiral galaxy	14500	Canes Venatici	9.5
      M95	NGC 3351		Spiral galaxy	38000	Leo	11.0
      M96	NGC 3368		Spiral galaxy	38000	Leo	10.5
      M97	NGC 3587	Owl Nebula	Planetary nebula	2.6	Ursa Major	12.0
      M98	NGC 4192		Spiral galaxy	60000	Coma Berenices	11.0
      M99	NGC 4254	Coma Pinwheel Galaxy	Spiral galaxy	60000	Coma Berenices	10.5
      M100	NGC 4321		Spiral galaxy	60000	Coma Berenices	10.5

      Messier number	NGC number	Common name	Object type	Distance to object in thousands of light years	Constellation	Apparent magnitude
      M101	NGC 5457	Pinwheel Galaxy	Spiral galaxy	24000	Ursa Major	8.5
      M102	(Actual identification unknown)
      M103	NGC 581		Open cluster	8	Cassiopeia	7.0
      M104	NGC 4594	Sombrero Galaxy	Spiral galaxy	50000	Virgo	9.5
      M105	NGC 3379		Elliptical galaxy	38000	Leo	11.0
      M106	NGC 4258		Spiral galaxy	25000	Canes Venatici	9.5
      M107	NGC 6171		Globular cluster	20	Ophiuchus	10.0
      M108	NGC 3556		Spiral galaxy	45000	Ursa Major	11.0
      M109	NGC 3992		Barred spiral galaxy	55000	Ursa Major	11.0
      M110	NGC 205		Dwarf elliptical galaxy	2200	Andromeda	10.0

      http://en.wikipedia.org/wiki/List_of_Messier_objects
      

      SUN
       
                When the weather is clear and the Sun is nicely positioned in the sky (such as when it is not too high or not too low, and if I have the Astroscan nearby, I usually bring it out for my students to see the Sun. I often just project the Sun’s image on a piece of paper or on a folder. Some people would not advise projecting the Sun because it might damage the internals of a telescope but the Astroscan is as good as ever despite having seen this kind of duty for many years now. I used the Astroscan to see and to show the students the latest transit of Mercury across the Sun, while holding the 8-inch solar filter in front of the telescope. But this is a rather dangerous configuration. A single mistake, such as when the hand holding the filter gets tired and momentarily puts it down, the person currently looking through the eyepiece will suddenly experience blinding light, I mean literally blinding. Looking through the Sun without a filter can cause sudden blindness!
      
                I miss the services of my Celestron 8-inch Schmidt-Cassegrain. I is now woefully out of collimation and I really do not know how to put its collimation back. A great part of all my observations were done with that instrument. I have done a lot of solar observations with the C-8, with its full size aperture filter. I have seen, together with hundreds of students and teachers, the rare transit of Venus across the Sun, and once the Mercury transit. Solar observation is a fascinating pursuit, if only we can find a better way of bearing the heat.

                The Sun is the local star in the Solar System. Its gravitational pull gives order to the components of the Solar System, particularly the planets. It is the source of heat and light for all the planets.

                Where does the Sun get its energy? According to Ian Ridpath in his book Stars and Planets,

                The Sun’s energy is generated at its core, where temperatures are estimated to reach 15 million degrees C or 27 million degrees F. Under these extreme conditions, hydrogen is converted to helium by nuclear fusion. Energy from these reactions travels outwards, first by radiation and then by convection, eventually reaching the photosphere. Above the photosphere is a less dense layer of gas, the chromosphere, from which bright clouds called prominences extend into the rarefied outermost region, the corona.
                 For how long has the Sun been burning? Stephen Maran in his book Astronomy for Dummies explains:

                The Sun produces energy at an enormous rate, equivalent to the explosion of 92 billion one-megaton bombs every second. That energy comes from the consumption of fuel. If the Sun were made of burning coal, it would burn up every last lump of itself in just 4,600 years. But fossil evidence on Earth shows that the Sun has been shining for more than 3 billion years, and astronomers are certain that its been going for longer than that.

                It is estimated that the Sun is 4.6 billion years old. About middle age, and it will keep on burning strong for several billions of years more.

                How big and how far is the Sun? If we look at the Sun through a welder’s filter, or through smoked glass or even old film negatives, we can compare the apparent size of the Sun to the eraser of a pencil held at arm’s length. Why don’t you try? When I ask my students how big is the Sun, some of them say it’s about as big as an orange, but can be as big as a watermelon when its rising behind the Sierra Madre mountains. About its size and distance, here is the explanation of Isaac Asimov in his book The Sun:

                This brilliant star is huge. It is about 93 million miles away (150 million kilometers). So it must be huge to be seen, at that distance in the sky, as such a large ball. It is about 865,000 miles across (1.390,000 km), 108 times as wide as Earth. It has 333, 400 times the mass of Earth. In fact, it has almost 1,000 times the combined mass of all the planets, satellites, asteroids, and comets circling it!

                Asimov further explains that “the Sun alone is bigger than the entire Earth-Moon system! Astronauts have traveled from Earth to the Moon, but they have not yet gone far enough to match the distance from the Sun’s center to the Sun’s surface.”

                The orbit of Earth around the Sun is not in a perfect circle. There are times when it is closer to the Sun than in other times. When is the closest approach of the Earth to the Sun and at what time of year is it farthest? According to Stan Gibilisco in his book Astronomy Demystified,

               The commonly accepted distance from Earth to the Sun is 150,000,000 kilometers (93,000,000 miles) in round numbers. But the day-to-day distance varies up to a couple of million kilometers either way… Earth’s closest approach to the Sun is called perihelion, and it occurs during the month of January. Earth is farthest away from the Sun – aphelion – in July.

                But why is it very cool in January, and very warm, or hot, in July?
      

      A	B

      A. AR 10486 Sunspot Group - This image was taken by the author on November 3, 2003.  It  resembles or appear to shape like a pregnant Seahorse or small baby fetus. B. AR0036 - Imaged on July 27, 2002 using CP995 att 17,100mm f/170 at 1/250sec at ISO 100..

      http://www.geocities.com/jkty5597/ June 25,2007

      

      Taken by James Kevin Ty using 4" f/5.4 TV-101 refractor, negative projection with 2x Big Barlow . E.F.L.= 1760mm f/18 at 1/2000 sec exposure on September 24, 2000 with Canon EOS 50E camera body on YKL 100 Film converted to grayscale

      http://www.geocities.com/CapeCanaveral/Hangar/6887/sun.html June 25, 2007

                The above images were taken by James Kevin Ty of the Astronomical League of the Philippines. He is a superb astrophotographer, and his images have been published in the Sky and Telescope magazine. I have yet to ask his permission to use his images in this book!

               When I use the 8-inch Schmidt-Cassegrain to study the Sun at high power, I can always see granulation and uneven surface features on this star. Ruby-Ann “The Bibang” Dela Cruz, calls them “an-an” on the surface of the Sun. Indeed they look like an-an. Let us read Asimov’s explanation of this:

      The Sun’s surface is not even. Parts of it are always rising, and, other parts are sinking. It’s a little bit like the water of Earth’s ocean that rises and fall in waves. As a result of this rising and sinking, the surface of the Sun seems to consist of grains, granules, or granulation cells of matter packed closely together. Each grain looks small to us on Earth, but on average it is nearly 600 miles (1,000 km) across! Although large, a granule does not live long. Each lasts about eight minutes. Then a new one forms, just as bubbles keep on replacing one another in a pan of boiling water. Scientists think that there are about four million granules on the Sun’s surface at any one time!

               And then there are the sunspots. Some of my students who have seen sunspots called them “tigyawat” or “tagihawat”, whichever way it is pronounced. At any rate, these are pimples in the Sun’s surface. The middle-aged Sun still has an occasional pimple! According to Ridpath,

              Sunspots, dark patches on the Sun’s surface, are actually areas of cooler gas. They can last from a few days to several months, and range in size from a few hundred kilometers across to complex groups extending for 100,000 km. Occasional eruptions near sunspots, called flares, shoot out atomic particles that reach the Earth and can cause glows in the atmosphere termed aurorae .

              Sunspots appear in cycles lasting about 11 years. According to Ridpath, “At the start of the cycle, spots are few in number and appear away from the equator. Approaching solar maximum, the spots become more numerous (with up to 100 visible at one time) and appear closer to the equator.”

              The solar cycle seems linked to the weather on Earth, though there is no conclusive proof about this yet. Giles Sparrow tells a story on how the lack of sunspots directly affected our weather. “The first sunspots were recorded around 1610 but, between 1645 and 1715 were seen,” Sparrow narrates. “This period,” Sparrow continues, “known as the Maunder Minimum, after the astronomer who first noticed it, coincided with the Little Ice Age of exceptionally cold winters in Europe and elsewhere. In London, the Thames froze regularly, and frost fairs were held on the ice.”

      

              The Sun is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the Solar System ( Jupiter contains most of the rest).

      http://www.nineplanets.org/sol.html June 25, 2007

              During meetings of the Astronomical League of the Philippines held usually in the Manila Planetarium, one of the most delightful parts of the meeting is the solar viewing done through an exquisite, and very expensive, telescope. It is the Coronado Solarmax, which shows a red Sun through a hydrogen-alpha filter, much like the image above. James Kevin Ty owns this instrument, a 40-mm telescope even smaller than my 9 x 50 finderscope. I will ask permission from James if I can bring my students to the meeting so they can view the solar flares and prominences which can be seen only through the h-alpha filter. According to Asimov,

              In areas around the sunspots, the gases are more active. Explosions near these spots give off a lot of energy. When waves from the explosions hit Earth, they even affect compasses on the planes and ships! These explosions called flares also shine brightly. So while the sunspots are somewhat cooler- around 8,100°F (4,500°C)- the flares are hot and more than make up for sunspots. When the Sun is particularly spotty, Earth is also a bit warmer than at other times .
              Those prominences, sometimes shaped like loops, are most particularly attractive as seen through the h-alpha filter. According to Asimov, they “lift off the Sun’s surface and erupt through its thin outer atmosphere, called the corona.”

      Core . The Sun's nuclear "furnace," where fusion reactions initially combine hydrogen atoms to produce helium, yielding energy in the process.
      Radiative Zone. Energy moves through a surrounding envelope of gas toward the Sun's surface.
      Convection Zone. Big "bubbles" of hot gas transport energy to the surface.
      Photosphere. The Sun's visible surface. Because of its high temperature, it glows yellow.
      Sunspot. A magnetic "storm" on the Sun's surface.
      Prominence. An eruption of hot gas that can extend thousands of miles into space.
      Corona . The Sun's outer atmosphere, which is heated by the magnetic field to millions of degrees.

      http://stardate.org/resources/ssguide/sun.html June 26, 2007

              The Sun will burn for many more billion years, but just like anything in the Universe, it will also die, or just fade away, like an old general:

              The Sun will continue to burn its hydrogen for several billion years more. As it depletes the supply of hydrogen, its core will shrink and temperatures will climb high enough for it to burn helium instead. The Sun's surface will puff up like a balloon, growing cooler, brighter, and redder, forming a red giant.

              Eventually, as the Sun burns helium to form heavier elements, it will reach a critical point where fusion cannot release enough energy to form new elements, so fusion will end.

              After that, the Sun will shed its outer layers, surrounding itself with a colorful bubble of gas called a planetary nebula. As the nebula dissipates, distributing carbon, oxygen, and other elements into the galaxy, only the Sun's collapsed core will remain -- a dense ball no bigger than Earth, containing about 60 percent of the Sun's original mass. This dead remnant is called a white dwarf. Over many billions of years, the white-dwarf Sun will cool and fade from sight, leaving behind a dark cosmic ember.

      The Sun At a Glance

      Classification G2V Main-Sequence Star Distance from Earth 92,955,800 miles 149,597,900 km 1 Astronomical Unit (AU) Mass 332,900 times Earth's mass Volume 1.3 million times Earth's volume Rotation Rate 25.38 Earth days (equator) Equatorial Diameter 864,400 miles 1,391,000 km 109 times Earth's diameter

      http://stardate.org/resources/ssguide/sun.html June 26, 2007

      MOON

                The Bible calls the Moon the “lesser light” or the “smaller light to rule the night” AND the stars, depending on the version you would consult. The Bible also states that the Day and the Night were created before the Sun, the Moon, and the stars were created.

                Filipinos believe a lot of things about the Moon, like the writers of the Bible. In his massive work Encyclopedia of Philippine Folk Beliefs and Customs, Fr. Francisco Demetrio relates that Filipinos believe that it is good to plant camote during the full Moon “so the result will also be as big as the moon.” And when you plant coconuts, it should be during full Moon “and do not turn back so that the fruits will be round and big.” It is also not good to cockfight during the last quarter Moon because roosters are weak during that day. And for lovers, it is good to time your courtship when a star is very near the Moon because “ladies easily accept suitors at this time.” There are a lot more of these beliefs, covering all of four pages in the Fr. Demetrio’s Encyclopedia. I would be a lunatic if I put all those beliefs here.

                The Moon is often the only object in the night sky most people will readily identify, and it is the most requested object during public stargazing sessions. Set up that telescope and ask the people around you what they want to see. They would look around and then point to the Moon. Initial reactions are varied. My compadre in Taytay Rizal, Sonny De Leon, exclaimed that it is “butas butas pala! Parang sementong naulanan.” One child, who probably spent much time on the beach, was reminded of the holes crabs dig on beaches. We see bright areas as well as dark areas on the Moon. Through a telescope, a huge amount of details can be observed such as valleys, craters, ridges, and wide dark plains. Galileo Galilei himself was the first man who saw and studied the Moon through a telescope. What he saw was heretical especially when he described it. He saw that the Moon’s surface was irregular, and there were even large cavities he thought contained water. The Moon was created by God, and God could not have created something imperfect especially if it is in heaven! Stan Gibilisco relates that:

                When Galileo announced that the Moon had craters and mountains, his fellow scientists became interested right away, but those who held power over people’s lives had other notions. To them, Galileo was a troublemaker, and he was treated as one. He ended up spending his last years under house arrest. It was not a tyrannical government dictator that subjected him to this, but the Pope. Imagine the reaction the Pope would get today if he demanded that some scientist spend the rest of his life under confinement!

      Let us now proceed to more scientific discussions.

      Stephen Maran in his book Astronomy for Dummies explains some of the properties of the Moon:

                The Moon is 2,160 miles (3,476 kilometers) in diameter, slightly more than ¼ the diameter of Earth. Its mass is only 1/81 the mass of Earth, which is 5.5 times the density of water. The Moon has no meaningful atmosphere, jus a trace of hydrogen, helium, neon, and argon atoms – and others in even lesser quantities. It appears to be made of solid rock.

                Bob Berman in his book Secrets of the Night Sky explains that the lunar soil is as fine as talcum. When astronauts strolled on the Moon, “Several inches deep, this baby powder crunching underfoot made strolls on the moon like hikes through the finest lakeside silt. Each footstep left deep impressions that will be more enduring, on the moon’s windless surface, than the greatest human monuments.”

                The Moon appears to us in phases. How would you know approximately what phase the Moon would be tonight? Do you have a kalendaryong intsik? Here is an illustration of the phases taken from the Internet.

       

      

      http://www.moonphases.info/moon_phases.html June 26, 2007

      

      • New Moon This is the first of the moon phases
      • Waxing Crescent Moon “Waxing" means growing and refers to the size of the illuminated part of the moon that is increasing.
      • First Quarter Moon  
      • Waxing Gibbous Moon
      • Full Moon

                The full moon occurs when the Moon lies on the opposite side of Earth from the Sun. The moon as seen from the surface of the earth is fully illuminated by the sun at this time, presenting a "full" round disc to viewers on earth. As always, only half the total surface of the moon is illuminated. The full moon reaches its highest elevation at midnight a full moon is the only time when a lunar eclipse is possible; at that time the moon may move through the shadow cast by the earth. However, because of the tilt of the moon's orbit around the earth relative to the earth's orbit around the sun, the moon may pass above or below the shadow, so a lunar eclipse does not occur at every full moon. Full moons are generally a poor time to conduct astronomical observations, since the bright reflected sunlight from the moon overwhelms the dimmer light from stars

      • Waning Gibbous Moon "Waning" means shrinking. When the Moon is said to be waning, we see a little less of the Moon each day until it completely disappears when the Moon is New.
      • Last Quarter Moon
      • Waning Crescent Moon

                In the northern hemisphere, if the right side of the Moon is dark, the light part is shrinking: the Moon is waning (moving towards a new Moon). If the left side is dark, the Moon is waxing (moving towards a full Moon). The acronym mnemonic "DOC" represents this ("D" is the waxing Moon; "O" the full moon; and "C" the waning moon). In the Southern hemisphere, this is reversed, and the mnemonic is "COD".

      http://www.moonphases.info/moon_phases.html June 27, 2007

                When I ask students how big the Moon is as compared with any object, some would say it is as big as an orange when rising but smaller when high up in the sky. Is this true? But there are times when it appears bigger than before. According to Stan Gibilisco in his book Astronomy Demystified,

                Maybe it’s not your imagination. The Moon orbits Earth in an elliptical path, with Earth at one focus. The Moon can get as close as 356,000 kilometers (221,000 miles) and as distant as 407,000 kilometers (253,000 miles) from Earth. This is a difference of 13.5% of the Moon’s mean distance .

                That difference will make the Moon appear 13.5% bigger, enough to be noticeable. The Moon’s closest approach is called lunar perigee, and its furthest retreat is called lunar apogee.

                Here are some photographs of some lunar features. Notice the impact craters with rays, craters with central peaks which might remind you of the tiny island in the crater lake of Taal Volcano, and the dark planes called marias.

      

                Ground-based view of moon crater Messier : Craters Messier and Messier A in Mare Fecunditatis are prominent from Earth because of the near parallel rays originating from them. Amateur observers can easily find them with medium powers.

       

                This photograph was possibly obtained from Yerkes Observatory and is an enlargement from an unlabeled print of a first-quarter Moon photo.

      http://antwrp.gsfc.nasa.gov/apod/ap990326.html June 27,2007

      

      Tycho crater on Earth's moon

      An impact crater is an approximately circular depression in the surface of a planet, moon or other solid body in the Solar System, formed by the hyper-velocity impact of a smaller body with the surface. Impact craters typically have raised rims, and they range from small, simple, bowl-shaped depressions to large, complex, multi-ringed, impact basins. Meteor Crater is perhaps the best-known example of a small impact crater on the Earth.

      http://en.wikipedia.org/wiki/Impact_crater June 26, 2007

      

      Moltke crater, a simple crater with a diameter of 4.3 miles (7 km).

      http://www.enchantedlearning.com/subjects/astronomy/moon/Craters.shtml June 27,007

      

      Euler crater, a complex crater with a diameter of 17 miles (28 km) and a depth of 1.5 miles (2.5 km).

      http://www.enchantedlearning.com/subjects/astronomy/moon/Craters.shtml June 26,2007

      

                Most of the craters on the Moon are circular. The few craters that are not circular, like Messier and Messier A (pictured at the left) in the Mare Fecunditatis, are an enigma. Scientists do not know exactly how these oddly shaped craters were formed.

      http://www.enchantedlearning.com/subjects/astronomy/moon/Craters.shtml June 26, 2007

                Since nobody had seen the other side of the Moon for centuries, some people thought the Moon was a half-shell! We can see only one face of the Moon because it is locked in synchronous rotation with Earth. It means that it makes exactly one turn on its axis as it makes one orbit around Earth. The orbital period of the Moon, and also the length of its day, is about 27 days, 7 hours, and 43 minutes.

                When Luna 3 of the USSR went to the Moon on October, 1959, it took pictures of the far side. Bob Berman describes what the pictures revealed:
                The first pictures were a shock. The two sides are so different, they’re almost visions of separate worlds. The back side, undoubtedly because of scantier tidal stresses induced by Earth, has had less volcanism in its distant past and consequently far fewer of the dark blotches that are so prominent on the side we see. Conversely, ancient craters buried by lava on the hemisphere facing us remain unscathed on the far side, which explains why that part of the moon is much more heavily cratered.

                Berman adds that the Russians lost no time giving names to the lunar features they discovered “in a wild orgy of name-dropping.” “To this day,” Berman says, “that all-Russian hemisphere remains a quiet embarrassment in U.S. textbooks, mitigated only by the fact that nobody on Earth will ever see any of it.” Now, here is a picture of the far side. The caption provides additional information.

                Locked in synchronous rotation, the Moon always presents its well-known near side to Earth. But from lunar orbit, Apollo astronauts also grew to know the Moon's far side. This sharp picture from Apollo 16's mapping camera shows the eastern edge of the familiar near side (left) and the strange and heavily cratered far side of the Moon. Surprisingly, the rough and battered surface of the far side looks very different from the near side which is covered with smooth dark lunar maria. The likely explanation is that the far side crust is thicker, making it harder for molten material from the interior to flow to the surface and form the smooth maria.

      http://antwrp.gsfc.nasa.gov/apod/ap981008.html June 28, 2007

      

                This image was taken by Apollo 11 astronauts in 1969. It shows a portion of the Moon's heavily cratered far side. The large crater is approximately 80 km (50 miles) in diameter. The rugged terrain seen here is typical of the far side of the Moon.

      http://www.solarviews.com/cap/moon/farside.htm June 28, 2007

                Where did the Moon come, or what is its origin? The current fashionable theory is the Giant Impact Theory. It says that an object, about 3 times the mass of Mars, struck the young Earth with a glancing blow. Of course that Earth was much more different from the Earth today. The present Moon is thought to contain material from the Earth and from the impacting object. Stephen Maran in his book Astronomy for Dummies explains how the Moon formed from this process:

                The Giant Impact on the young Earth knocked all this material up into space as a vapor of hot rock. It condensed and solidified like snowflakes. The snowflakes knocked into each other and stuck together, and before you know it, the Moon had formed. Coming together in powerful impacts of the last big pieces of accumulated rock, the Moon was melted by heat from the impacts.

                Maran adds that this theory is so far the best, but he clarifies that “Unfortunately, no one can think of a basic test for the…theory…So it’s a good theory, but we may really never know what made the Moon.” God, perhaps?

      The Giant Impact , as pictured in a painting by William K. Hartmann on the cover of Natural History Magazine in 1981. Copyright William K. Hartmann

      At the time Earth formed 4.5 billion years ago, other smaller planetary bodies were also growing. One of these hit earth late in Earth's growth process, blowing out rocky debris. A fraction of that debris went into orbit around the Earth and aggregated into the moon.

      Half an Hour After the Giant Impact , based on computer modeling by A. Cameron, W. Benz, J. Melosh, and others. Copyright William K. Hartmann

      Five Hours After Impact , based on computer modeling by A. Cameron, W. Benz, J. Melosh, and others. Copyright William K. Hartmann

      Moon Forming Out of RingsCopyright William K. Hartmann

      http://www.psi.edu/projects/moon/moon.html June 29, 2007
      
              One very nice activity in astronomy is watching lunar eclipses. According to Maran, “A lunar eclipse occurs when the full Moon is exactly on the line from the Sun to the Earth. Then the Moon is in Earth’s shadow, the umbra.” Unlike viewing solar eclipses, it is perfectly safe to look at a lunar eclipse, “as long as you don’t bump into something in the dark or stand in the road,” Maran cautions.

              One memorable lunar eclipse I observed with my students on the Roof Deck of the RTU Pasig Campus was on January 9 to 10, 2001 using the Astroscan. In my Observation Report Number 70 in Volume II of my work Urban Astronomy in thePhilippines, I recorded that the shadow completely engulfed the Moon at about 3:50 a.m. without using sophisticated timing devices, just my watch. I though the moment of totality was “numinous”. Here is part of my observation report:

              The eclipse provided us a view of the Moon in an entirely new light, literally. To most of us the sky is flat. The stars and planets and the Moon are like multi-colored lights pasted on the dark surface. Some are small, some are bright, but they seem to be equidistant. The sky is like a dome, not the vast space it really is. The lunar eclipse created a three-dimensional view of space. The Moon seemed like an orange ball, spherical in shape, not a flat dish when seen in ordinary light. It was like it was suspended in space with the background stars providing a hallowed backdrop but was immensely farther… this is a sanctified view consecrated by the Creator Himself. The accompanying stars themselves were like ordained attendants accompanying the sublime Anointed, and with the exception of one, all keeping distance.
      
      

       MERCURY

              One of the hardest planets to see is Mercury because either you wait for it just after the Sun goes down or you wake up just before the Sun comes up. There are not too many people in our country, or even the whole world who have seen this planet. Once you have recognized this planet, however, you will not mistake it for anything else anymore. At least on two occasions I have shown the transits of Mercury across the Sun, a tiny round dot crossing a yellow ball, that was how the students who saw the transits described the event.

              Mercury, as we all know, is the closest planet to the Sun. There were efforts to locate another planet nearer to the Sun than Mercury, but they all failed.

       

      

      http://www.space.com/php/multimedia/imagegallery/igviewer.php?imgid=2697&gid=209 ( June 8,2007)

       

              Now let us study the profile of Mercury.
              Mercury’s day and year is unique among the planets. Robert M. Nelson in an essay in the book The Scientific American Book of the Cosmos explains that

              In 1955 astronomers were able to bounce radar waves off Mercury’s surface. By measuring the so-called Doppler shift in the frequency of the reflections, they learned of Mercury’s 59-day rotational period. Until then, Mercury had been thought to have an 88-day period, identical to its year, so that one side of the planet always faced the Sun.

              This means that Mercury rotates three times for each two orbits around the Sun. On Earth, one day in Mercury is equal to 59 day, but if we are at Mercury, the time for the Sun to return to the same place in Mercury’s sky is two Mercury years, or 176 Earth days. So if you text your classmate to see you at noon the following day, it would take a very long time!

             Mercury has the most elliptical orbitof all the planets. According to the Oxford Dictionary of Astronomy, “at perihelion it is only 46,000,000 km from the Sun, but 69, 820,000 km at aphelion.” Nelson shows us that “When Mercury is at perihelion…it moves so swiftly that, from the vantage of someone on the surface, the Sun would appear to stop in the sky and go backward – until the planet’s rotation catches up and makes the Sun go forward again.”

              The Oxford Dictionary of Astronomy describes Mercury as having the “most extreme temperature range of any planet in the Solar System, becoming extremely hot during the day, nearly 430 degrees C at the subsolar point at perihelion, and rapidly dropping below -183 degrees C during the long dark night.”

       

      

      http://www.space.com/php/multimedia/imagegallery/igviewer.php?imgid=2698&gid=209 ( June 8,2007)

              The equatorial plane of Mercury is tilted by only two degrees relative to the plane of its orbit around the Sun. This may have some interesting prospects, as explained by Giles Sparrow in his book The Universe and How To See It:

              Mercury orbits the Sun bolt upright, and as a result the planet’s poles only ever see the Sun close to the horizon. This means that deep craters in these dark areas are kept in permanent darkness, and may shelter large ice deposits dumped by comets that have collided with Mercury .

       

      

      http://www.space.com/php/multimedia/imagegallery/igviewer.php?imgid=2703&gid=209 ( June 8,2007)

      Mercury is pockmarked with craters. Stacey Palen in his book Astronomy describes the surface of Mercury:

              Mercury is heavily cratered like the Moon, but also contains large patches of craterless terrain. This implies that the surface of Mercury is younger than the surface of the Moon. Perhaps Mercury remained geologically active longer because it is larger than the Moon and closer to the Sun. Cooling of the interior has caused the crust to crack and shift vertically, producing “scarps,” which are cliffs several kilometers high and hundreds of kilometers long. A particularly spectacular impact left the Caloris Basin, a large impact crater about 1,300 kilometers in diameter, surrounded by circular ripples. On the opposite side of mercury from the Caloris Basin, the surface topography is dramatically disturbed, apparently by the shock waves of the impact. This region is called the weird terrain .

              Mercury’s atmosphere is a surprise to many astronomers when it was discovered. Mercury is not supposed to have an atmosphere, but it has. Nelson explains this phenomenon:

              Objects as hot as Mercury do not, however, retain appreciable atmospheres around them, because gas molecules tend to move faster than the escape velocity of the planet. Any significant amount of volatile material on Mercury should soon be lost to space. For this reason, it had long been thought that Mercury did not have an atmosphere. But the ultraviolet spectrometer on Mariner 10 detected small amounts of hydrogen, helium and oxygen, and subsequent Earth-based observations have found traces of sodium and potassium.

              Nelson further explains that such atmosphere could be material created by the solar wind that blows material off the surface of the planet, from the planet’s magnet-osphere, or from cometary material.

       

      

      http://www.space.com/php/multimedia/imagegallery/igviewer.php?imgid=2708&gid=209 ( June 8,2007)

              Mercury has an unusually high gravity. According to Sparrow, “it is three-quarters the size of Mars, yet has the same surface gravity. This would be explained if the planet contained an abnormally large amount of heavy material – an oversize iron and nickel core, for instance.” Stephen Maran in his book Astronomy for Dummies adds that

              Mercury has a density 5.4 times of water. This high density means that Mercury has a huge iron core that constitutes the bulk of the planet. The outer layer of rock, called the mantle, must be no more than 380 miles (610 kilometers) thick. The presence of a global magnetic field, detected around Mercury by Mariner 10, suggests to many experts that some of that huge iron core must still be molten, although simple calculations indicate that the core should have cooled enough to solidify by now.

      Here are additional planetary data of Mercury:

      PLANETARY DATA – MERCURY

      Sidereal period	87.969 days
      Rotation Period	58.6461 days
      Mean orbital velocity	47.87 km/s (29.76 miles/s)
      Orbital inclination	7°00” 15”.5
      Orbital eccentricity	0.206
      Apparent diameter	Max 12”.9, min 4”.5
      Reciprocal mass, sun = 1	6,000,000
      Density, Water = 1	5.5
      Mass, Earth = 1	0.055
      Volume, Earth	0.056
      Escape velocity	4.3 km/s (2.7 miles/s)
      Surface gravity, Earth = 1	0.38
      Mean surface temperature	350°C (day); -170°C (night)
      Oblateness	Negligible
      Albedo	0.06
      Maximum magnitude	-1.9
      Diameter	4878 km (3030 miles)

       

       

       

           

                                                                                           

VENUS
By Dr. Jesus Rodrigo F. Torres

          What is the brightest object in the sky next to the Sun and the Moon? It is Venus, the second planet from the Sun.

          Venus appears in the night sky either as the Evening Star or as Morning Star, but a lot of people do not know what it is. Some even mistake it for a UFO. I myself was asked not a few times about that “bright object that seems to move”. A few years ago, Venus was very close to Jupiter and that was the time when these questions were most numerous. I remember having set up my Celestron 4-inch achromatic refractor to view the two planets. They fit in the field of view of the 40-mm eyepiece. The view was surreal. The two planets were in the same line of sight and almost the same angular diameter but we know that Jupiter is vastly more distant from us than Venus.

          Bob Berman in his classic book Secrets of the Night Sky relates to us some instances when Venus has been mistaken for a UFO:

          Every nineteen months, when the Evening Star reaches its maximum brilliance and lights up the western twilight like a searchlight, Earth’s inhabitants go on a binge of misidentification. Some years, according to one prominent UFO author and researcher, bright planets (with Venus leading the charge) account for more than half of all UFO reports, and such sightings don’t all come from dimwits. Jimmy Carter, while governor of Georgia, phoned the state police to report a UFO that proved to be Venus. A few years later the CBS Evening News featured footage of a UFO filmed by an Australian camera crew; this UFO also turned out to be the cloud-shrouded planet. And a squadron of Allied bombers returning from a mission over Japan in World War II saw a brilliant light that appeared to keep pace with them. Firing their guns, they attempted, without success to blow up the Evening Star.

          Because Venus is a lovely object to look at, it is named after the goddess of beauty herself. According to Berman, “Goddess of love, certainly – as the night’s brightest ‘star’ it’s appropriate that Venus be forever associated with love…But it’s strictly a ‘look but don’t touch’ affair”. As explained by Stan Gibilisco in his book Astronomy Demystified, “as the literal facts about Venus emerged from flybys and landings that took place in the mid-twentieth century, it became clear that the surface of Venus is neither lovely nor a beautiful place. In fact, conditions there resemble medieval humanity’s conception of hell.”

          Less poetic, perhaps, but not less informative is the description of this “hell” by Stacey Palen in his book Astronomy in the Schaum’s Outline series:

          The atmosphere on Venus consists of carbon dioxide (96%) and nitrogen (3%). The atmosphere is so thick that the pressure at the surface of Venus is 90 times the atmospheric pressure on the surface of the Earth. This is roughly equivalent to the pressure 0.5 mile under the surface of an ocean on Earth. The high pressure (plus the CO 2 atmosphere) drives the temperature to a scorching 740 K, which remains quite uniform around the planet. Lead is a liquid at these pressures and temperatures, which make it quite a challenge to design a spacecraft that can land there and remain functional long enough to take useful data. Higher up in the atmosphere, clouds of sulfuric acid are common.

          It rains on Venus, and the rain never stops. According to Stephen P. Maran in his book Astronomy for Dummies, “The bad news about the weather on the surface of Venus is that a perpetual rain of sulfuric acid falls all over the planet. The good news is that this rain is a virga, meaning rain that evaporates before it hits the ground.”

          What about the surface of Venus? There are no seas in this planet because there is no water. According to Maran, “The few images we have from Venus lander spacecraft, as pioneered by the former Soviet Union, show areas of flat rock plates, separated by small amounts of soil. They look like some areas of hardened basalt lava flows on earth. But on Venus, things look like orange at the surface, because the thick cloud cover has filtered the sunlight.” Orange, everything looks orange on Venus! Berman describes Venus as much worse than Purgatory. “It’s the Other Place”, he says, “the destination of people who do bad things like touch lenses with fingers. Temperatures on its surface stay uniformly hellish, as if regulated by a thermostat from some stygian sauna.”

          Maran further describes the topography of the planet: “Flat plains, volcanic lowlands with rilles (the winding canyons left by lava flows) cover the vast majority of Venus (about 85 percent). This territory includes the longest known rille in the solar system, Baltis Vallis, which stretches across Venus for about 4, 230 miles (6,800 kilometers). Cratered highlands and deformed plateaus are also present on Venus.” About these craters, Maran informs us that there are not much craters on Venus. Here’s why:

          There aren’t as many craters on Venus as you would expect based on the number of them on Earth’s Moon (Venus has no known moon of its own) and on Mercury. No small craters exist. There aren’t many large craters because the surface of Venus was flooded with lava or reworked by volcanism after its bombardment by impacting objects had mostly ended. This flooding or reworking erased all or most of the early craters. Few large objects have struck Venus since the early craters were destroyed, and small objects don’t make craters up to two miles in diameter are impeded and destroyed by aerodynamic forces in the thick Venus atmosphere.

          The hellish temperature of Venus is directly attributed to the greenhouse effect. This phenomenon is here explained by Dr. Palen:

          CO 2 is a greenhouse gas. It reflects infrared radiation in the atmosphere toward the surface, where it becomes trapped. This keeps heat in the atmosphere, rather than releasing it to space. The CO 2 atmosphere on Venus is the result of a runway greenhouse effect. Early in history, Venus probably had about the same proportion of water and CO 2 that the Earth did at that time. But because Venus is closer to the Sun, and therefore warmer, the water never condensed out into the oceans. The oceans on Earth regulate the amount of CO 2 in the air by trapping carbon deep in the ocean, which get recycled back into rocks. Without these oceans, the CO 2 on Venus remained in the atmosphere. As volcanoes added CO 2 to the atmosphere, there was nowhere for it to go – it just remained in the atmosphere, further increasing the temperature. As the CO 2 concentration increased, the temperature increased. With no way to remove CO 2 from the atmosphere , the temperature continued to increase as volcanic activity processed, until the atmosphere reached the hot, dense state it is in now.

          This runaway greenhouse effect can happen here on our very own Planet Earth. Andrew Franknoi, David Morrison, and Sidney Wolff in their book Voyages to the Planets explain how:

          We want to emphasize that the runway greenhouse effect is not just a larger greenhouse effect; it is revolutionary process. The atmosphere evolves from having a small greenhouse effect, such as on the Earth to a situation where greenhouse warming is a major factor, as we see today on Venus. Once the larger greenhouse conditions develop, the planet establishes a new, much hotter equilibrium near its surface. Reversing the situation is difficult because water vapor in the planets atmosphere is not stable in the presence of ultraviolet light. Ultraviolet light from the Sun tends to breakdown the molecules of H 2 O into their constituent parts -- oxygen and hydrogen. The light element hydrogen can escape from the atmospheres of the terrestrial planets, leaving the oxygen behind to combine chemically with surface rock. The loss of water is therefore an irreversible process; once the water is gone, it cannot be restored. There is evidence that this is just what happened to the water once present in Venus.

          They give warning that “Venus stands as clear testament to the fact that a planet cannot continue heating indefinitely without a major change in its oceans and atmosphere. It is a conclusion that we and our descendants will surely want to pay close attention to.”

Venus

Mean distance from the Sun (km) 108.2 million Mean distance from the Sun (AU) 0.72333 Eccentricity 0.00677 Sidereal period(d) 224.701 Equatorial diameter (km) 121044 Equatorial diameter (relative to Earth’s) 0.95 Sidereal rotation period (d) 243 retrograde Inclination 1773° Mass(kg) 4.8689x10 24 Mass(relative to Earth’s) 0.95 Density(relative to water) 5.24 Escape velocity (km s -1 ) 10.36 Escape velocity(relative to Earth’s) 0.93 Albedo 0.65 Surface temperature 740 K

MARS

        Despite my interest in observing deep-sky objects I took the opportunity to observe and sketch Mars during its nearest approach to Earth in 2003. I was able to compile quite a few sketches with my 10-inch Orion Dobsonian reflector. On August 28, 2003, the very day of Mars’ closest approach to Earth, I set up the 8-inch Celestron Schmidt-Cassegrain telescope at the RTU Roofdeck in the Pasig Campus; that campus still had a roofdeck back then. The sky was hazy and there was threat of rain, but Mars did not spoil the occasion. Perhaps a hundred students were able to witness the event. Here is an Internet account of Mars’ approach:

        In the year 2003, Mars has come as close to Earth as it didn't come in millennia, not to speak of lifetimes. Mars opposition occurred on August 28, 2003 ( 17:58:49 UT), less than two days before the planet passes its perihelion on August 30. The closest approach of the two planets had already occurred one day earlier, on August 27 ( 09:51:14 UT); distance will be as close as 55.758 million km (more acurately, 55,758,006 km or 34,646,418 miles). At this distance, it appeared larger than at any historic time to now: 25.11 arc seconds in diameter.

        This is the closest approach since a time of 59,619 years, when in 57,617 B.C., the planet came still a very little bit closer, 55.718 million km, and exhibited an apparent diameter of 25.13 seconds of arc. The next encounter closer than the current 2003 one will occur on August 28, 2287, when Mars will be observable at an apparent diameter of 25.14".

        At such a close distance, the planet has brightened up to visual magnitude -2.9, and appeared under an apparent diameter of 25.11 arc seconds; it outshone Jupiter notably (would even if that planet were in favorable opposition), and was only second to planet Venus.

http://www.seds.org/~spider/spider/Mars/mars2003.html ( June 8, 2007)

        Mars is a mysterious planet and we still have a lot to learn about it.

        It had water but where did the water go? This phenomenon is explained quite simply in this website:

        Water most likely flowed in the distant past on Mars, carving channels and other features clearly visible on its surface. But other than in the form of clouds and ice, liquid water cannot exist on the planets surface today, thanks to the thinness of its atmosphere.

        Scientists have hypothesized that vast stores of water could still persist beneath the surface of Mars.

 

http://www.space.com/scienceastronomy/solarsystem/mars_water_story_000620.html ( June 8, 2007)

        According to Stephen Maran in his book Astronomy for Dummies, Mars is dry now, but there is still a great deal of ice in its poles. “By one estimate,” Maran continues, “enough ice is present to flood the entire planet to a depth of 100 feet if it were melted. But the ice won’t melt; Mars is just too cold.” Maran further explains :

        The atmosphere is mostly carbon dioxide, and in winter, some of that gas freezes on the surface, leaving thin deposits of dry ice. At the pole where winter is under way, a thin cap of dry ice often tops the permanent cap of water ice. Dry riverbeds with streamlined islands, and pebbles, that look like they’ve been rounded in a torrent, are among the other evidence for past liquid water on Mars. The pebbles were imaged with the mars Pathfinder (which landed on Mars) and its little robot, Sojourner.

Stereo images of rock "Moe" - This stereo image close-up was taken from the Sojourner rover's front cameras on 70 (September 13). Flute-like textures on the rock, possibly caused by wind abrasion, are clearly visible.

http://nssdc.gsfc.nasa.gov/planetary/marspath_images.html ( June 8, 2007)

        Mars Pathfinder lander on sol 39 - This image was taken by the rover's left front camera. Deflated air bags arvisible at the base of the spacecraft. The American flag and the letters "JPL" are seen on Pathfinder's white electronics housing. The mast for the Pathfinder camera extends upward from the top of the housing. The front rover ramp is perched on top of the air bags and is several feet above the ground. Because of this precarious position, Sojourner used the rear ramp to reach the surface on Sol 2. The large rock visible behind the air bags is "Yogi."

http://nssdc.gsfc.nasa.gov/planetary/image/marspath_sol39l.gif ( June 8, 2007)

        Mars Pathfinder image 80904 - Named Twin Peaks, the formation of two hills in the background are of extreme geological interest. The left hill has a smooth apron which may have been caused by gravitational processes or water. The hill on the right seems to have horizontal bands running through it. As of yet unidentified, the bands may be deposits, sedimentary layers, or terraces cut by erosion.
The twin peaks are approximately 1 km from the Sagan Memorial Station. The rocks in the foreground are very diverse. Some are rounded and suggest transport by water, others are tabular and angular and indicate non-aqueous deposition. Preliminary hypotheses by Pathfinder geologists are that the angular rocks were thrown from ancient, nearby impact crater sites.

http://nssdc.gsfc.nasa.gov/planetary/marspath_images_bw.html ( June 8, 2007)

        The biggest known volcano in the Solar System is on Mars. It is Olympus Mons. The dimensions of this volcano is astounding. Let us read more of this volcano from this website:

Olympus Mons

        Olympus Mons is the largest volcano in the solar system.  It stands 17 kilometers high, which is three times as high as Mount Everest.  The caldera, the depression at the center of the volcano, spans 80 kilometers across. Olympus Mons is a shield volcano, similar to those found in Hawaii, but considerably larger.   One reason for this is that Mars does not have plate tectonics, the movement of a planet's crust.  Consequently, the volcano is situated above a hot spot for millions of years, allowing for repeated eruptions that build up the surrounding structure.   There is some evidence that Olympus Mons may be the remains of an even larger volcano.

        The lava that flowed from Olympus Mons created snakelike channels that stretch several hundred kilometers long and 200 meters across.  These flows are much larger than their Earth counterparts, which rarely extend more than 30 kilometers, and are not much wider than 10 to 30 meters.

         Olympus Mons has been extinct for several hundred million years, which is relatively young in geological terms and makes it the youngest volcano on Mars. 

http://www.sff.net/people/ckanderson/olympus.htm ( June 8, 2007)

        There are also many canyons on Mars, including the very large Valles Marineris which is about 4,000 kilometers long. Let us learn more about this geological feature:

Canyons and Valles Marineris

        The great canyon system of Valles Marineris stretches 4000 kilometers across Mars. This figure shows part of Ius Chasma, the southwestern part of the Valles Marineris. The region shown here is 600 kilometers across.

http://www.lpi.usra.edu/expmars/activities/valmar.html ( June 8, 2007)

        The craters of Mars are worn down by erosion, probably caused by great floods in Mars’ past. Here is an excellent image of eroded craters on Mars:

Eroded Highland Terrain

         Rather than the relatively blocky craters found on the Moon, the oldest terrain on Mars shows degradation of crater rims and evidence of erosion by running water. A comparison of the number of craters in the Martian highlands versus those on the Moon suggests that even the earliest crust of Mars may have long since been buried by more recent volcanic deposits.

http://www.nasm.si.edu/ceps/etp/mars/surface/craters.html

        Mars has two moons, and they are both tiny. We can read below that they are probably captured asteroids, but their nearly circular orbits. The Earth captures asteroids from time to time, the latest is Asteroid 2003 YN107, an asteroid measuring only 20 meters across and too small to be seen with the naked eye. Here are some notes on Mars’ moons:

Phobos, a world of mysterious origin

        Phobos is a world of mysterious origin and destiny. It is light, with a density less than twice that of water, and orbits just 5989 km above the Martian surface. Recent observations by Mars Global Surveyor have revealed that the surface is covered in one metre thick dust, suggesting erosion due to meteor bombardment as the lack of atmosphere rules out other means. One idea is that Phobos and Deimos, Mars's other moon, are captured asteroids. Data returned by the infrared mapping spectrometer experiment on board the Phobos 2 mission supported this view

Deimos

        Unlike the Earth, which has one oversized satellite (the Moon), Mars has two very small satellites. Asaph Hall at the Naval Observatory in Washington D.C. discovered them in August 1877 and they were named after the nasty twin children of Mars, who are mentioned in a few scattered lines of the Iliad. Deimos means 'terror' or 'panic' and Phobos means 'fear' (or, possibly, 'rout' in the mind of Homer).

        Both satellites have equatorial, almost circular orbits, with Phobos orbiting once every 7 h 39 min just 5989 km from the surface of Mars and Deimos orbiting once every 30 h 18 min at 20 062 km from the surface of the planet. The orbital period of Phobos is three times faster than the rotation period of Mars, with the unusual result among natural satellites, that Phobos rises in the west and sets in the east as seen from Mars. Also, it orbits so close to the surface of Mars that the curvature of the planet would obscure its view from an observer standing in Mars' polar regions.

The two bodies are too light for gravity to make them spherical. Both are somewhat potato-shaped, with major diameters of 22 km for Phobos and 12 km for Deimos. Phobos, at least, has a very lumpy appearance. It is heavily cratered and is covered with dust one metre thick, suggesting that it has suffered heavy meteor bombardment. Both satellites are probably composed of carbon-rich rocks. In 1988, Phobos 2, one of the last great scientific missions of the Soviet Union, detected outgassing from the satellite, but could not ascertain its nature because the spacecraft malfunctioned before fully accomplishing its objectives

http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31031( June 8, 2007)

        A lingering question is whether there is life on Mars. In the 19th and early 20th centuries, when planetary photography was not yet so well developed, and there were no Pathfinders and Mariners yet, astronomers speculated about the possibility of life on mars. Percival Lowell saw features on mars which he theorized to be canals built by ancient civilizations on mars designed to channel water to the cities from the Martian poles. The American spacecraft Mariner 4 reached Mars in 1965. The photographs it took showed no canals. The Viking Orbiters debunked through close-up photographs what appeared initially as a face on Mars. Now, a rock from Mars found in Antartica is now thought to contain fossils of microbes. Here is an image of the fossil, from the rock designated ALH 84001:

 

http://en.wikipedia.org/wiki/Life_on_Mars ( June 8, 2007)

What is the latest news on research about the possibility of life on Mars?

Here are some sketches I made. Can you identify the surface features in the sketches?

 

 

Planetary data - Mars

Sidereal period Rotation period Mean orbital velocity Orbital inclination Orbital eccentricity Apparent diameter Reciprocal mass, Sun =1 Density, Water = 1 Mass, Earth =1 Volume, Earth = 1 Escape velocity Surface gravity, Earth = 1 Mean surface temperature Oblateness Albedo Maximum magnitude Diameter (equatorial)

686.980 days 24hb37m 22s.6 24.1 km/s (15 miles/s) 1° 50’ 59”.4 0.093 max 25”.7, min 3”.5 3,098,700 3.94 0.107 0.150 5.03 km/s (3.1 mile/s) 0.380 -23°C 0.009 0.16 -2.8 6,794 km (4222 miles)

                                                                                           ASTEROIDS 

        Whenever I hear asteroids, I often remember the late Dr. Danilo Aguirre of the RTU. He could probably outdrink anybody in the Milky Way when he was alive. Since he and Dr. Luis Castaneda often joined me in my early observations conducted on the RTU Pasig Campus Roof Deck, I asked them to join the Philippine Astronomical Society. The Society was still conducting its meetings at the Manila Planetarium then, and Father Victor Badillo was still very strong then, and it was James Kevin Ty who was president. I brought Danny to the Planetarium to make official his being an astronomer and he dutifully filled up the application form and gave it to Father Badillo afterwards. In the entry for what interests the applicant most, he checked “asteroids”. Father Badillo asked him “Why, have you seen one?” Danny replied “Hindi pa nga Father, kaya yan ang nilagay ko!” Father Badillo himself is now an asteroid, I mean an asteroid has been named after him. It is asteroid 1988VB3 now known as Asteroid 4886 Badillo.

        I haven’t seen one myself. I have seen galaxies millions of light years away but I have not seen an asteroid. The marvel of modern technology, however, brings asteroids right in our offices or living rooms. You just have to use the Internet. Some asteroids, like Ceres, was classified as a planet once. Here are some images of asteroids:

Ceres

The classification of Ceres has changed more than once and has been the subject of some disagreement. At the time of its discovery it was considered a planet; but within forty-nine years it was reclassified by many astronomers as an asteroid. This lasted for over 150 years; and was first classified a dwarf planet in 2006.

Johann Elert Bode believed Ceres to be the "missing planet" that Johann Daniel Titius had proposed to exist between Mars and Jupiter, at a distance of 419 million km (2.8 AU) from the Sun. Ceres was assigned a planetary symbol, and remained listed as a planet in astronomy books and tables (along with 2 Pallas, 3 Juno and 4 Vesta) for about half a century until further asteroids were discovered. However as further objects were discovered in the area it was realised that it represented the first of a class of many similar bodies. Sir William Herschel coined in 1802 the term asteroid ("star-like") for such bodies, [12] writing "they resemble small stars so much as hardly to be distinguished from them, even by very good telescopes". [13] As the first such body to be discovered, it was given the designation 1 Ceres under the modern system of asteroid numbering.

http://en.wikipedia.org/wiki/1_Ceres June 25, 2007

Ida

Ida and Dactyl

Ida is a heavily cratered, irregularly shaped asteroid in the main asteroid belt between Mars and Jupiter -- the 243rd asteroid to be discovered since the first one was found at the beginning of the 19th century. Ida is placed by scientists in the S class (stony or stony iron meteorites). It is a member of the Koronis family, which scientists believe was created when a larger body perhaps 200 to 300 kilometers (120 to 180 miles) in diameter was smashed relatively recently -- at least considerably after the solar system formed some 4.5 billion years ago.

On August 28, 1993 Galileo came within 2,400 kilometers (1,500 miles) of 243 Ida, the second asteroid ever encountered by a spacecraft. They passed each other at a relative velocity of 12.4 km/sec (28,000 mph). At the time of the encounter, Ida and Galileo were 441 million kilometers (274 million miles) from the Sun.

Ida is about 56 x 24 x 21 kilometers (35 x 15 x 13 miles) in size, more than twice as large as Gaspra. It has a period of rotation of 4 hours, 38 minutes. Its density has been estimated to be between 2.2 and 2.9 grams per cubic centimeter. Ida's age is somewhat baffling. Its surface is heavily cratered suggesting that it has existed in its present form for at least a billion years and perhaps much longer. It is also considerably older than estimates for the Koronis breakup.

http://www.solarviews.com/eng/ida.htm June 25, 2007

Gaspra

http://nssdc.gsfc.nasa.gov/image/planetary/asteroid/gaspra.jpg June 25, 2007

Stephen Maran in his book Astronomy for Dummies calls asteroids “leftovers of the birth of the Solar System.” Most of them reside in the Asteroid Belt, the area of the Solar System between the orbits of Jupiter and Mars. There are also asteroids that move along the orbit of Jupiter. They are called Trojan asteroids. Another group cross the Earth’s orbit. They are called Apollo asteroids. They are dangerous asteroids since they might collide with Earth. They are also called Near Earth Objects or NEOs. Have you seen the movies Armageddon and Deep Impact? These films try to depict what might happen if a 6-kilometer asteroid strikes Earth, as one asteroid of that size hit Earth 65 million years ago. According to Stephen Maran in his book Astronomy for Dummies, “The Chicxulub crater, a 110-mile (180-kilometer) wide geologic formation that is partly on Mexico’s Yucatan peninsula and partly offshore in the Gulf of Mexico, may be the surviving trace of this impact, which is said to have wiped out the dinosaurs. (It certainly didn’t do them any good.)”

What should humans do, or what can we do, if we discover an asteroid that will strike Earth? Some scientists propose to blast the asteroid by a powerful nuclear missile, but that might give us more problems. According to Maran, “If we blew up an asteroid with a nuclear bomb, a swarm of smaller rocks – instead of one big rock heading for Earth – would be on that deadly trajectory, like the warheads on a multiple independently targeted reentry vehicle or MIRV.” Maran cautions that each of the rocks would be deadlier than any of the weapons of the Pentagon, so the better alternative would be to nudge the asteroid out of its path so it will miss Earth. Now that it has been proven that we can land on an asteroid, this alternative is very possible, BUT we have to FIND the threatening asteroid FIRST.

By the way, a few more asteroids have been named after Filipinos. They are 6282 Edwelda after Edwin Aguirre and Imelda Joson; Josette Biyo and her students Allan Noriel Estrella, Jeric Valles Macalintal and Prem Vilas Fortran were also given the honor of asteroids being named after them: 13241 Biyo, 11697 Estrella, 12088 Macalintal, and 12522 Rara. The latest Filipino asteroid was named after the late scientist Roman Kintanar, 6636 Kintanar.

JUPITER

http://spaceflightnow.com/news/n0010/07cassinijupiter June 13, 2007

One of the brightest objects you can see in the night sky is Jupiter. It is often the third brightest object next to the Moon and Venus, and very occasionally Mars, and except when a supernova explodes that could be visible even during the day! Jupiter is big and round even through 7 x 50 binoculars and at 17x in the Astroscan. Often visible are the four Galilean moons -- Ganymede, Io, Callisto, and Europa, except if one or two of them are hiding behind the big planet, or are so close together in the line of sight. Many students I have shown Jupiter are surprised to see how round it is, the first object besides the Moon they have seen to be round. But I tell them to look closely and see that Jupiter is not that round: it is slightly flattened, like a ball used for sitting. It is very big. According to Patrick Moore in his book Atlas of the Universe, “it has only 1/1047 of the mass of the Sun [yet] it is more massive than all the other planets combined.”

The disk of Jupiter is obviously flattened, and this is because of its rapid rotation. According to Moore, “Jupiter’s ‘year’ is almost twelve times ours, but the ‘day’ amounts to less to less than ten hours.” The Earth’s polar diameter is 42 kilometers shorter than its equator, but Jupiter’s polar diameter is 10,000 kilometers shorter than its equatorial bulge.

The outer clouds of Jupiter are very cold but it gets steadily hotter inside the planet. According to Stephen Maran in his book Astronomy for Dummies,

Up at the atmospheric levels…the temperatures drop to -236 degrees F…But at great depths, the squeeze is on. By the time you’ve reached 6,200 miles (10,000 kilometers) below the clouds on Jupiter, the pressure has soared to one million times the barometric pressure at sea level on Earth. And the temperature equals that of the visible surface of the Sun! But Jupiter is weirder than the Sun. The density of the thick gas at this depth is much higher than at the solar surface, and the hot hydrogen is compressed so that it behaves like liquid metal.

Take a few moments to imagine it: hydrogen behaving like liquid metal!

When you look at Jupiter through a small telescope, you will immediately notice two orange belts bisecting it in the middle. With bigger telescopes and with higher magnification, there are so many of these belts with various hues and colors, and they do not look the same all the time. According to Maran, “What you see in your telescope when you view Jupiter is really the top of the planet’s clouds.” The center of the planet is the Equatorial Zone. Flanking it are the North and South Equatorial Belts ( NEB and SEB). Stan Gibilisco in his book Astronomy Demystified explains that “The typical wind speeds on Jupiter…are many times greater than those we consider normal on our planet. In the extreme, Jovian winds exceed 400 kilometers per hour, comparable with gales inside the most severe Earthly tornadoes.”

One feature of Jupiter you must see is the Great Red Spot. I have never seen it with the same color, though I could not really tell if it changes shape or not. Sometimes it is quite pale but at times it looks a little too red. My best views of it were in my 102-mm Celestron refractor. The GRS, as astronomers call it, is a storm three times the size of the Earth. It has been there for centuries.

Jupiter has a ring, but it is not visible from here. There would have been two planets with nice rings around it! Information for this ring is here gathered from Wikipedia (2007):

The Jovian ring system is faint and consists mainly of dust. [1] [5] It comprises four main components: a thick inner torus of particles known as the 'halo ring'; a relatively bright, razor-thin 'main ring'; and two wide, thick and faint outer 'gossamer rings', named for the moons of whose material they are composed: Amalthea and Thebe.

The main and halo rings consist of dust ejected by high-velocity impacts from the moons Metis, Adrastea and other unobserved parent bodies. [2] High-resolution images obtained in February–March 2007 by the New Horizons spacecraft revealed a rich fine structure in the main ring

http://en.wikipedia.org/wiki/Rings_of_Jupiter June 12, 2007

At more than 400x in my Orion 10-inch Newtonian reflector, I have seen a moon of Jupiter casting a shadow on the face of the planet. It should be a good observing project to monitor the positions of the Jovian moons. I have not made a serious effort to track down these moons because my interest is really in deep-sky observing but if you want to, the website of the Sky and Telescope magazine will teach you how.

Maran gives us the following information about the Galilean moons of Jupiter:

At 3,274 miles in diameter (5,268 kilometers), Ganymede is larger than 3,033-mile-wide Mercury (4,880 kilometers) and is the largest moon in the solar system. Ganymede’s blotchy surface consists of light and dark terrains, perhaps ice and rock, respectively. The most noticeable marking is Valhalla, a huge ringed impact basin, about as large as the continental United States (judging the size by the outermost ring-ridge).

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Ganymede

(http://quest.arc.nasa.gov/lfs/tguide/na3.html

June12 2007

Io’s surface is peppered with more than 80 active volcanoes. It is the only place other than Earth where we have definite evidence of ongoing volcanism. Most likely, the volcanoes on Mars are long dead, and the evidence for active volcanism on Venus is very controversial- big volcanoes are discernible, but they are probably dead, too.

                                                                            Io
(http://quest.arc.nasa.gov/lfs/tguide/na3.html) June12 2007

Europa has a ridge terrain that looks like rafts of ice. The surface may be frozen crust that tops off an ocean of water and slush, perhaps 90 miles (150 kilometers) deep. It is the only place in the solar system, outside of Earth, where we have strong evidence that liquid water is present. The existence of liquid water on Mars, beneath a layer of permafrost, is only a theory.

Europa (http://quest.arc.nasa.gov/lfs/tguide/na3.html June12 2007Callisto has a dark surface, with many white craters. This surface is probably dirty ice, a mixture of ice and rock. Where asteroids, comets, and big meteoroids struck, the underlying clean ice has been exposed. Hence, the white craters.

Callisto (http://quest.arc.nasa.gov/lfs/tguide/na3.html June12 2007

One other surface feature of Jupiter we should know is the Red Spot Jr., a smaller version of the Great Red Spot. Christopher Go, an amateur astronomer from the Philippines, who has been observing and imaging Jupiter for years, noticed that the spot was reddening. He is credited to have named this feature the Red Spot Jr.

PLANETARY DATA

Sidereal period Rotation period (equatorial) Mean orbital velocity Orbital inclination Apparent diameter Reciprocal mass, sun = 1 Density, Water = 1 Mass, Earth = 1 Volume, Earth = 1 Escape velocity Surface gravity, Earth = 1 Mean surface temperature Oblateness Albedo Maximum magnitude Diameter (equatorial) Diameter (polar)

4332.59 days 9h 55m 21s 13.06 km/s (81 miles/sec) 1° 18’ 15” .8 max 50” .1, min 30” .4 1047.4 1.33 317.89 1318.7 60.22 km/s (37.42 miles/sec) 2.64 -150°C 0.06 0.43 -2.6 143,884 km (89,424 miles) 133,700 km (83,100 miles)

How many moons does Jupiter really have? Why are the Galilean moons called by such name?

SATURN

http://stuff.mit.edu/afs/athena/contrib/xpix/images/gif/saturn.gif June 13, 2007

Perhaps the most beautiful object that can be seen in the sky is Saturn. I often show this planet to my students to finally hook them to astronomy. Some veteran observers reserve Saturn for the last but I show it right away. Maybe the best thing is to prepare an observing plan when conducting those public astronomy lectures so the lecturer would not run out of the sky’s greatest hits.

Saturn has been compared with Jupiter but there are many differences between the two planets. Saturn has a lower mass and smaller size, and is almost twice as far away from the Sun as Jupiter. According to Stan Gibilisco in his book Astronomy Demystified, “Saturn orbits the Sun at a distance of 9.54 AU. It orbital radius is about 1,430 million kilometers.” Further, Gibilisco informs us that “Saturn takes 29.5 Earth years to make a complete revolution around the Sun with respect to the distant stars.” This is important for astronomers to know because it has been computed that Saturn reaches opposition every 12 ½ months. Viewing the planet is best done when it is at opposition.

Saturn is comprised of very light materials. According to Asimov, “If Saturn were hollow, you could pack 833 Earths into it. But Saturn has the mass of only 95 Earths.” Gibilisco further explains Saturn’s composition:

Saturn is comprised of about three-quarters hydrogen and one-quarter helium, with trace amounts of ice, methane, ammonia, and silicate molten rock. The inner core is where this mineral matter is found; if all the hydrogen and helium on Saturn were blown away, the remaining body would be a planet similar to Earth but several times more massive. As with Jupiter, the inner core is surrounded by liquid metallic hydrogen mixed with helium. As we progress further and further from the center of the globe, the liquid hydrogen becomes nonmetallic; then it becomes a dense gas, thinning out and topped with yellowish clouds…

As explained by Patrick Moore in his book Atlas of the Universe, “the overall density of the globe of Saturn is less than that of water – it has even been said that if the planet could be dropped into a vast ocean it would float!” I have read somewhere, however, that if we can ever find an ocean big enough to float Saturn, that ocean could not exist because its mass would cause it to form a more compact object much denser than water!

Saturn has a turbulent weather. Stephen Maran in his book Astronomy for Dummies relates that “Saturn has belts and zones, just like Jupiter, but they have less contrast and are much harder to see.” Some features of Saturn are as interesting as its rings. According to Maran,

About once every 30 years, a big white cloud or “greta white storm” appears in the Northern Hemisphere of Saturn. High speed winds spread the cloud out until it forms a thick, bright band all the way around the planet. Months later it’s all gone. Sometimes amateur astronomers are the first to spot a new storm on Saturn. The last great white storm was in 1990, so you may have to wait a long while to see another. In the meantime, keep an eye out for smaller white clouds that spread partway around the planet. Saturn spins once every 10 hours, 39 minutes, and 22 seconds and is even more oblate – flattened at the poles – than Jupiter. The rings tend to mislead the eye a little, however, and seeing Saturn looking squashed can be tricky.

It is interesting to note that Saturn was once considered as a triple planet. According to Isaac Asimov in his book Saturn, The Ringed Beauty, Galileo “became the first person to see Saturn through a telescope. It was the farthest known planet at the time, and he couldn’t see it clearly. It seemed to have ‘ears’ on each side!” A few months later the “ears” disappeared and Galileo could not explain how it happened.

When observing the rings, our immediate target is to see the Cassini Division, a dark gap in the rings. Astronomers have classified the different portions of the ring into a series of rings named A Ring, B Ring up to the G Ring. How thick are the rings? According to Gibilisco, “The rings are extraordinarily thin in proportion to their width…Estimates of the ring’s thickness range between 100 meters and 1 kilometer.”

The rings are comprised of chunks of icy materials ranging in size from grains the size of dust to boulders as big as a house. How did the rings form, and why do they remain in their orbit instead of just being sucked up by the giant planet? Here is the explanation of Gibilisco pertaining to these phenomena:

The ring system presents several mysteries. Astronomers think they have solved some of these, but others remain inexplicable. One theory holds that the rings formed from the breakup of an icy moon that ventured too close to Saturn and was torn apart by gravitational forces. Every planet’s gravitational field, even that of the Earth, has a minimum orbital radius within which large natural satellites cannot stay in one piece. This is known as the Roche limit. For Saturn, the Roche limit is roughly 2½ times the radius of the planet. Boulder-sized rocks and even a few small asteroids continue to orbit Saturn in one piece within this limit; the maximum size depends on what the particle is made of. There are a few especially large boulders that orbit Saturn inside the ring system, and these are believed to be responsible for the gaps, also called divisions, that appear in the ring system.

The rings showing the radial spokes. According to Moore, they are presumably particles elevated away from the ring-plane by magnetic or electrostatic forces.

http://www.planetary.org/explore/topics/saturn/rings.html June 13, 2007

Even in light-polluted urban locations, it is possible to see five moons of Saturn. The moons Enceladus, Titan, Tethys, Rhea and Dione show up in various positions every night, but they could be in the same line of sight or behind or too close to the planet. Anyway, Saturn has a family of disparate moons. Here are some of them:

                                                                  Tethys

ith this full-disk mosaic, Cassini presents the best view yet of the south pole of Saturn's moon Tethys.

The giant rift Ithaca Chasma cuts across the disk. Much of the topography seen here, including that of Ithaca Chasma, has a soft, muted appearance. It is clearly very old and has been heavily bombarded by impacts over time.

Many of the fresh-appearing craters (ones with crisp relief) exhibit unusually bright crater floors. The origin of the apparent brightness (or "albedo") contrast is not known. It is possible that impacts punched through to a brighter layer underneath, or perhaps it is brighter because of different grain sizes or textures of the crater floor material in comparison to material along the crater walls and surrounding surface.

The moon's high southern latitudes, seen here at the bottom, were not imaged by NASA's Voyager spacecraft during their flybys of Tethys 25 years ago.

The mosaic is composed of nine images taken during Cassini's close flyby of Tethys (1,071 kilometers, or 665 miles across) on Sept. 24, 2005, during which the spacecraft passed approximately 1,500 kilometers (930 miles) above the moon's surface.

his view is centered on terrain at approximately 1.2 degrees south latitude and 342 degrees west longitude on Tethys. It has been rotated so that north is up . http://www.solarviews.com/eng/tethys.htm June 13, 2007

Dione

The cratered and cracked disk of Saturn's moon Dione looms ahead in this mosaic of images taken by Cassini on Oct.11, 2005, as it neared its close encounter with the icy moon.

The images used for this mosaic are clear-filter views, which reveal a great deal of surface detail.

Multiple generations of tectonics can be seen in this full-disk view. Near the eastern limb (at the right) are tectonic fractures, which may be similar to the bright, braided canyons that make up Dione's noted wispy terrain. Some of the bright, wispy markings can be seen at the left.

The softer ridges and troughs at the upper right appear to be about the same age as the cratering seen in that region. These appear to be older than the fracturing seen in the wispy terrain and the fractures seen at the right.

Scientists continue to be intrigued by the strikingly linear features seen crisscrossing the southern latitudes. The fine latitudinal streaks appear to crosscut everything, and appear to be the youngest feature type in this region of Dione.

A large impact basin hugs the south polar region (at the bottom, right of center). Northeast of the basin is a region of terrain that is relatively smooth, compared to the rest of the moon .

http://www.solarviews.com/cap/pia/PIA07746.htm June 13, 2007

                                                                       Enceladus

Enceladus [en-SELL-ah-dus] is one of the innermost moons of Saturn. It is quite similar in size to Mimas but has a smoother, brighter surface. Enceladus reflects almost 100 percent of the sunlight that strikes it. Unlike Mimas, Enceladus displays at least five different types of terrain. Parts of Enceladus shows craters no larger than 35 km in diameter. Other areas show regions with no craters indicating major resurfacing events in the geologically recent past. There are fissures, plains, corrugated terrain and other crustal deformations. All of this indicates that the interior of the moon may be liquid today, even though it should have frozen aeons ago. It is postulated that Enceladus is heated by a tidal mechanism similar to Jupiter's moon Io. It is perturbed in its orbit by Saturn's gravitational field and by the large neighboring satellites Tethys and Dione. Because Enceladus reflects so much sunlight, the surface temperature is only -201° C (-330° F).

http://www.solarviews.com/eng/enceladu.htm June 13, 2007

 

Rhea

Rhea [REE-a] is the largest airless satellite of Saturn. It was discovered in 1672 by Giovanni Cassini. Rhea is an icy body with a density of 1.33 gm/cm 3. The low density indicates that it is composed of a rocky core taking up less than one-third of the moon's mass, with the rest composed of water-ice. Rhea is somewhat similar to Dione. They both have similar composition, albedo features, varied terrain and synchronous rotations. The temperature on Rhea is -174°C (-281°F) in direct sunlight and between -200°C and -220°C (-328°F and -364°F) in the shade.

Rhea is heavily cratered with bright wispy markings. Its surface can be divided into two geologically different areas based on crater density. The first area contains craters which are larger than 40 kilometers (25 miles) in diameter. The second area, in parts of the polar and equatorial regions, has craters under 40 kilometers (25 miles) in diameter. This suggests that a major resurfacing event occurred some time during its formation. http://www.solarviews.com/eng/rhea.htm June 13, 2007

PLANETARY DATA -SATURN

Sidereal period Rotation period (equatorial) Mean orbital velocity Orbital inclination Orbital eccentricity Apparent diameter Reciprocal mass, Sun = 1 Density, Water = 1 Mass, Earth = 1 Volume, Earth = 1 Escape velocity Surface gravity, Earth = 1 Mean surface temperature Oblateness Albedo Maximum magnitude Diameter (equatorial) Diameter (polar)

10,759.20 days 10h 13m 59s 9.6 km/s (6.0 miles/s) 2° 29’ 21”.6 0.056 max 20.9”, min 15”.0 3498.5 0.71 95.17 744 32.26 km/s (20.05 mile/s) 1.16 -180°C 0.1 0.61 -0.3 120,536 km (74,914 miles) 108,728 km (67,575 miles)

 

TITAN

The brightest moon of Saturn we can see through a telescope is Titan. It is the second largest moon in the Solar System, next to Ganymede. Titan has an atmosphere. From an Internet source, we get a glimpse of the properties of Titan’s atmosphere:

Alone of all the satellites in the solar system, Titan has a significant atmosphere. At the surface, its pressure is more than 1.5 bar (50% higher than Earth's). It is composed primarily of molecular nitrogen (as is Earth's) with no more than 6% argon and a few percent methane. Interestingly, there are also trace amounts of at least a dozen other organic compounds (i.e. ethane, hydrogen cyanide, carbon dioxide) and water. The organics are formed as methane, which dominates in Titan's upper atmosphere, is destroyed by sunlight. The result is similar to the smog found over large cities, but much thicker. In many ways, this is similar to the conditions on Earth early in its history when life was first getting started. But it is this thick hazy atmosphere that makes it so hard to see Titan's surface.

http://www.seds.org/nineplanets/nineplanets/titan.html June 15, 2007

Voyager 1 came within 4,000 kilometers of the surface of the satellite but its cameras could not penetrate the thick haze of Titan’s atmosphere. What’s going on below the orange shield of its atmosphere? Here are some images from the Cassini spacecraft on a mission to Titan and from the Huygens probe that actually landed on the moon.

 

Radar image of Titan showing that the boundary of the bright (rough) region and the dark (smooth) region appears to be a shoreline. The image is 175 kilometers high and 330 kilometers wide (109 miles by 205 miles), and is located at 66 degrees south latitude, 356 degrees west longitude in the southern hemisphere of Titan. Image credit: NASA/JPL

http://www.space.com/scienceastronomy/050917_titan_shore.html June 15,2007

 

http://www.esa.int/SPECIALS/Cassini-Huygens/SEMEMY71Y3E_2.html June 18,2007

Titan is a very big moon. It is even larger than Mercury, a bona fide planet, and Pluto, a former planet. If Titan is larger than Mercury, why is Titan called a moon and Mercury a planet?

Is it possible for life to exist on Titan? It is possible. Stan Gibilisco in his book Astronomy Demystified tells us that “The main reason scientists find Titan so interesting is that it contains an abundance of organic chemicals.” Gibilisco points out that the term organic “does not mean that these chemicals were produced by or are necessarily indicative of living things in the environment.” It means that “Methane and ethane, hydrocarbons similar to natural gas, are considered organic because they have the potential to give rise to amino acids under the right conditions.”

Here is another speculation on the subject:

Carl Sagan and others tried to reproduce these organics in the laboratory. What they recovered was a sort of brownish sludge they called "tholin", from the Greek word "Tholos", meaning mud. Biologists believe that when our planet was formed, these molecules, some of which, like hydrogen cyanide or cyanoacetylene, are called prebiotic, contributed to the development of life. The laboratory simulations show that molecules of even higher complexity could be expected on Titan.

http://www.lifeinuniverse.org/noflash/Titanintro-06-02-01.html June 15, 2007

URANUS

The day I first saw Uranus was a memorable day. It was October 5, 2000 when I saw both Uranus and Mercury for the first time. A lot of students also saw Mercury in the Celestron 102-mm as I called them to the RTU Pasig Campus roof deck after I have confirmed to myself that it was indeed Mercury that I was seeing. One of those students was Ruby “The Bibang” Dela Cruz, now a science teacher in the RTU. Later in the night I carefully searched for Uranus among the stars of Capricornus using a wide range of magnifications. Uranus had a definite disk and was light blue, like the color of a record book where I wrote my observations then. Dr. Luis Castaneda who used to join me in observing thought it was whitish-blue but changed his mind later and said it was really blue. It was definite that we were only the two persons in the RTU who have seen Uranus in person at that time.

Uranus is a planet so far away it is hard to imagine really how far away it is from the Sun. If Saturn is twice as far away from the Sun as Jupiter, Uranus is twice as far away from the Sun as Saturn! Why is Uranus blue? According to Giles Sparrow in his book The Universe and How To See It, Uranus’ “distinctive turquoise color arises from a small percentage of methane gas in its atmosphere, which absorbs red light and reflects other colors.”

Among all the planets, Uranus is unique in its tilt on its axis. While the earth, for example, is tilted 23 degrees on it axis, Uranus is tilted 98 degrees! It is practically rolling sideways while revolving around the Sun. Even the rings and satellites of the planet revolve around it in the same plane as the tilt. Patrick Moore in his book Atlas of the Universe informs us that “The reason for this exceptional tilt is not known.” Moore explains that “It is often thought that at an early stage in its evolution Uranus was hit by a massive body and literally knocked sideways.” This may be hard to believe but Moore tells us that “it is hard to think of anything better.”

The unusual tilt creates some very curious happenings in Uranus’ seasons. Moore explains that “The Uranian calendar is very curious. Sometimes one of the poles is turned toward the Sun, and has a ‘day’ lasting for 21 Earth years, with a corresponding period of darkness at the opposite pole.” The poles in Uranus receive more heat from the Sun than does the equator! Uranus is so far away that it takes 84 Earth years for it to make one orbit around the Sun.

What is the nature of Uranus’ atmosphere? Moore states that is “is not easy to decide just where the atmosphere ends and the real body of the planet begins…” It seems that Uranus is one big ball of gas floating in space. Sparrow has additional information about this:

Like all the gas giants, Uranus’ outer layers are made mostly of the light gases hydrogen and helium. Deeper down, the planet contains large amounts of ices – chemicals such as ammonia and methane that evaporate into gas closer to the Sun. The high pressure inside Uranus turns these ices into an electricity-conducting slush, which swirls around, generating a magnetic field. Because Uranus’ magnetism is not generated in its rocky core, the field is very strange – pointing sharply away from the planet’s axis of rotation and not even passing through its center.

The rings of Uranus have been known since 1977 but direct images were captured only by Voyager 2 during its visit to the planet in 1986. Here are some details about the Uranian rings:

Astronomers have identified 13 rings of debris encircling Uranus’s equator. An inner set of extremely dark, narrow rings orbit the planet in the plane of its equator at distances from 38,000 km (24,000 mi) from the center of the planet. Many of these rings are made of ice and rock boulders about the size of large beach balls. Several observatories first detected five of the ten rings in 1977. Starting from the innermost ring, these five rings were called Alpha, Beta, Gamma, Delta, and Epsilon. In 1986 images taken by the Voyager 2 spacecraft helped scientists discover five more rings encircling Uranus. In 2005 astronomers using the Hubble Space Telescope reported the discovery of two new rings. These rings are so far from the planet that they make up a second ring system. The innermost of these more distant rings is about 67,000 km (41,632 mi) from the planet’s center and the outmost about 97,700 km (60,708 mi) from the center.
http://encarta.msn.com/encyclopedia_761551985_2/Uranus.html#s16 June 19, 2007

Here is an album on the moons of Uranus. You will not find such a family with so many dissimilar members anywhere.

 

So far the only close-up images of Umbriel are from the Voyager 2 probe, which made observations of the moon during its Uranus flyby in January, 1986. During the flyby the southern hemisphere of the moon was pointed towards the Sun so only it was studied.

Umbriel's surface is the darkest of the Uranian moons, and it is also the least geologically active. It is mostly composed of water ice, with the balance made up of silicate rock, and probably other ices such as carbon dioxide and/or methane.

Umbriel's most prominent feature is Wunda, a large ring of bright material near Umbriel's equator (see picture; the viewpoint is nearly polar). Wunda is presumably some kind of crater, but its exact nature is mysterious. Nearby, seen along the terminator, is the crater Skynd, which lacks a bright rim but possesses a bright central peak .

http://en.wikipedia.org/wiki/Umbriel_(moon) June 19, 2007

 

 

So far the only close-up images of Titania are from the Voyager 2 probe, which photographed the moon during its Uranus flyby in January, 1986. At the time of the flyby the southern hemisphere of the moon was pointed towards the Sun so only it was studied.

Although its interior composition is uncertain, one model suggests that Titania is composed of roughly 50% water ice, 30% silicate rock, and 20% methane-related organic compounds. A major surface feature is a huge canyon that dwarfs the scale of the Grand Canyon on Earth and is in the same class as the Valles Marineris on Mars or Ithaca Chasma on Saturn's moon Tethys .

http://en.wikipedia.org/wiki/Titania_(moon) June 19, 2007

 

 

So far the only close-up images of Oberon are from the Voyager 2 probe, which photographed the moon during its Uranus flyby in January, 1986. At the time of the flyby the southern hemisphere of the moon was pointed towards the Sun, so the northern hemisphere could not be studied.

Although its interior make-up is uncertain, one model suggests that Oberon is composed of roughly 50% water ice, 30% silicate rock, and 20% methane-related carbon/ nitrogen compounds. It has an old, heavily cratered, and icy surface which shows little evidence of internal activity other than some unknown dark material that apparently covers the floors of many craters.

So far, scientists recognise only two types of geological features on Oberon: craters and chasmata

http://en.wikipedia.org/wiki/Oberon_(moon) June 19, 2007

 

 

The first and so far only close-up observations of Ariel were made by the Voyager 2 probe during its 1986 Uranus fly-by. Voyager 2 made its closest approach of Ariel on January 24, 1986 and passed within 127,000 km of the moon. [2] Because the moon's south pole was pointed towards the Sun, only the southern hemisphere was photographed.

Ariel's composition is roughly 70% ices (water ice, carbon dioxide ice, and possibly methane ices) and 30% silicate rock, and it appears to have regions of fresh frost in places, particularly in the ejecta radiating from young impact craters. The oldest and most extensive geologic unit observed on Ariel by Voyager 2 was a vast area of cratered plains centered near Ariel's south pole. Analysis of craters seen on Ariel's cratered plains suggest most are younger than many of those seen on Titania, Oberon, and Umbriel. [3] The largest crater observed on Ariel is Yangoor, at only 78 km across, and shows signs of deformation since its formation. Voyager 2 also observed a network of faults, canyons, and icy outflows running along Ariel's mid-southern latitudes, breaking up the cratered plains region. The canyons probably represent grabens formed by extensional faulting. Smooth material and grooves are often seen running down length of Ariel's valley networks, suggested that some canyon floors have been covered in warm ice extruded from Ariel's interior.

Ariel's past geologic activity is believed to have been driven by tidal heating at a time when its orbit was more eccentric than currently. Early in its history, Ariel was apparently captured in a 4:1 orbital resonance with Titania, from which it subsequently escaped. [4] The resonance would have increased orbital eccentricity; resulting tidal friction due to time-varying tidal forces from Uranus would have caused warming of the moon's interior. In the Uranus system, due to the planet's lesser degree of oblateness, and the larger relative size of its satellites, escape from a mean motion resonance is much easier than for satellites of Jupiter or Saturn.

http://en.wikipedia.org/wiki/Ariel_(moon) June 19, 2007.

 

 

Miranda's surface may be mostly water ice, with the low density body also likely containing silicate rock and organic compounds in its interior.

Miranda's surface has patchwork regions of broken terrain indicating intense geological activity in the moon's past, and is criss-crossed by huge canyons. Large grooved structures, called coronae, may be diapirs, or upwellings of warm ice. The grooves probably represent cryovolcanic ridges formed by fissure eruptions of icy magma. The canyons probably represent grabens formed by extensional faulting. The diapirs may have changed the density distribution within the moon, which could have caused Miranda to reorient itself, [3] an event similar to what is believed to have occurred on Saturn's geologically active moon Enceladus. Miranda is one of the few bodies in the solar system in which the equatorial circumference is shorter than the pole-to-pole circumference, likely a consequence of the diapir activity.

Miranda's past geological activity is believed to have been driven by tidal heating at a time when its orbit was more eccentric than currently. Early in its history, Miranda was apparently captured in a 3:1 orbital resonance with Umbriel, from which it subsequently escaped. [4] The resonance would have increased orbital eccentricity; resulting tidal friction due to time-varying tidal forces from Uranus would have caused warming of the moon's interior. In the Uranus system, due to the planet's lesser degree of oblateness, and the larger relative size of its satellites, escape from a mean motion resonance is much easier than for satellites of Jupiter or Saturn. Miranda's orbital inclination (4.34°) is unusually high for a body so close to the planet. Miranda probably escaped from its resonance with Umbriel via a secondary resonance, and the mechanism of this escape is believed to explain why its orbital inclination is more than 10 times those of the other large Uranian moons (see Uranus' natural satellites).

An earlier theory, proposed shortly after the Voyager 2 flyby and now out of favor, was that a previous incarnation of Miranda was shattered by a massive impact, with the fragments reassembling into the current strange pattern.

http://en.wikipedia.org/wiki/Miranda_(moon) June 19, 2007

http://pds-rings.seti.org/uranus/ June 19, 2007

 

 

http://www.spaceflightnow.com/news/n0411/10uranusrings June 19, 2007

NEPTUNE

Neptune was definitely harder to find than Uranus. Unlike when I found Uranus with the 102-mm Celestron refractor, I had to use the 200-mm Celestron Schmidt-Cassegrain telescope to see Neptune. At 200x in the 6.3-mm Plossl eyepiece, Neptune appeared as a pale light-blue disc. The night I saw this object was memorable: it was October 21, 2001, and we played the championship game of the Administration-Faculty basketball league, and my team lost. I scored only 17 points in that game, my lowest point production since we started playing the league in the RTU gym. Later, after the game, some officials brought out some brandy for the University Week finale and I had a few drinks, but the sky was so clear so I decided to go to the RTU Pasig Campus for some observing. All of these seem a very long time ago…

I had the idea of observing Neptune from reading Sue French’ Small Scope Sampler column in the Sky and Telescope October, 2001 issue. Sue French explains that

Neptune is not a deep-sky object, but the 7.9-magnitude planet spends September and October between Omicron and Upsilon [Capricornii]… Neptune is the brightest object in this area; it looks like a tiny, pale turquoise fuzzball at high powers. Since the Latin poets called Capricornus “ Neptune’s Offspring”, this is a fitting place for the distant planet. It’s even more appropriate considering that Neptune was discovered while in this constellation.

From the book The Cosmos, Astronomy in the New Millenium by Jay Passachoff and Alex Filippenko, we can have a glimpse of some of the properties of Neptune:

Neptune is even further from the Sun than Uranus 30 A.U. compared about 19 A.U. Neptune takes 164 years to orbit the Sun. Its discovery was a triumph of the modern era of Newtonian astronomy. Mathematicians analyzed the amount that the Uranus (then the outermost known planet) deviated from the orbit it would follow if gravity from the Sun and the other known planets were acting on it. The small deviation could have been caused by gravitational interaction with another, as yet unknown planet…

Voyager 2 measured Neptune’s average temperature: 59K that is 59 C° about above zero. This temperature though low, is higher than would be expected on the basis of solar radiation alone. Neptune gives off about 2.7 times as much energy as it absorbs from the Sun. Thus there is an internal source of heating.

Why is the average density of Uranus and Neptune higher than that of Jupiter and Saturn? It may reflect slight difference in the origins of those planets. Their densities show that Uranus and Neptune have a higher percentage of heavy elements than Jupiter and Saturn. Perhaps the rocky cores they built up from the solar nebula were smaller, giving them less gravity and thus attracting less hydrogen and helium. Or, perhaps the positions of Uranus and Neptune farther out in the solar nebula put them in a region where either the solar nebula was less dense, or their slower orbital motion moved them through less gas.

Neptune ’s rings are “so much brighter when seen backlighted”, according to Passachoff and Filipenko. This will tell us about “the sizes of particles in them.” So, what do these particles say about Neptune’s rings? According to the two astronomers,

The most detectable parts of the rings have at least a hundred times more dust-size grains than most of the rings of Uranus and Saturn. Since dust particles settle out of the rings, new sources must continually be active. Probably moonlets collide and are destroyed.

Neptune 's rings, taken by Voyager 2

Neptune has a faint planetary ring system of unknown composition. The rings have a peculiar "clumpy" structure, the cause of which is not currently understood but which may be due to the gravitational interaction with small moons in orbit near them.

Evidence that the rings are incomplete first arose in the mid-1980s, when stellar occultation were found to occasionally show an extra "blink" just before or after the planet occulted the star. Images by Voyager 2 in 1989 settled the issue, when the ring system was found to contain several faint rings. The outermost ring, Adams, contains three prominent arcs now named Liberté, Egalité, and Fraternité ( Liberty, Equality, and Fraternity). The existence of arcs is very difficult to understand because the laws of motion would predict that arcs spread out into a uniform ring over very short timescales. The gravitational effects of Galatea, a moon just inward from the ring, are now believed to confine the arcs.

Several other rings were detected by the Voyager cameras. In addition to the narrow Adams Ring 63,000 km from the centre of Neptune, the Leverrier Ring is at 53,000 km and the broader, fainter Galle Ring is at 42,000 km. A faint outward extension to the Leverrier Ring has been named Lassell; it is bounded at its outer edge by the Arago Ring at 57,000 km.

New Earth-based observations announced in 2005 appeared to show that Neptune's rings are much more unstable than previously thought. In particular, it seems that the Liberté ring might disappear in as little as one century. The new observations appear to throw our understanding of Neptune's rings into considerable confusion.

http://en.wikipedia.org/wiki/Neptune June 20, 2007

By the way, the rings of Neptune have curious names. A committee of the International Astronomical Union named the major rings Le Verrier Adams, and Galle. Can you tell us why? And then the Adams ring has arcs which are named Liberte’, Fraternite’ and Egalite’.

 

This is an image of Neptune's Great Dark Spot of 1989.

http://www.windows.ucar.edu/tour/link=/neptune/atmosphere/N_clouds_GDS.html June 20, 2007

The Great Dark Spot was a dark spot on Neptune similar in appearance to Jupiter's Great Red Spot. Although it looked nearly the same as Jupiter's spot, it was not thought to be a storm but instead an atmospheric hole similar to the hole in Earth's ozone layer.

The spot was detected by NASA's Voyager 2 probe, which passed Neptune in 1989. It was comparable in size to Jupiter's spot, and was located in Neptune's southern hemisphere. Winds measured in the spot traveled at speeds up to 2400 km/h (1500 mph), the highest of any planet. The spot appeared to change as the spacecraft flew by, and does so in many pictures of it. The spot was believed to have been rotating counterclockwise. Concentrated regions of crystal methane and frozen water particle clouds resembling Earth's cirrus clouds were discovered over the Great Dark Spot.

When the Hubble Space Telescope viewed Neptune again in June 1994, the spot had vanished. However, another spot very much like the old one appeared in the planet's northern hemisphere later that year. [1] It is not known why the Great Dark Spot appeared nor whether it is a common occurrence or a rarer phenomenon. Its atmosphere is mainly hydrogen and helium. Some scientists think the movement of the Great Dark Spot is because of the 2250 km/h (1400 mph) jet stream winds on Neptune.

http://en.wikipedia.org/wiki/Great_Dark_Spot June 20, 2007

An interesting feature of Neptune was the Great Dark Spot, a storm discovered by Voyager 2 in its flyby to the planet in 1989. In 1994, the storm was no longer there as confirmed by the Hubble Space Telescope, but new storms were afterwards discovered, one with the curious name of Scooter.

Galileo was actually the first person to have seen Neptune but he did not know it was the planet. He even recorded its position. The existence of Neptune was deduced when astronomers noticed slight perturbations in the orbit of Uranus due to gravitational interactions with another object yet unknown. Once again, let us read the story from Passachoff and Filippenko’s book:

The first to work on the problem successfully was John C. Adams in England. In 1845, soon after he graduated from Cambridge University, he predicted positions for the new planet. But neither of the two main astronomers in England made and analyzed observations to test this position quickly enough. A year later, the French astronomer Urbain Leverrier independently worked out the position of the undetected planet. The French astronomers didn’t test his prediction right away either. Leverrier sent his predictions to an acquaintance at Berlin, where a star atlas had recently been completed. The Berlin observer, Johann Galle, discovered Neptune within hours by comparing the sky against the new atlas.

Neptune is 4, 498 million kilometers for the Sun or 30 A.U. (astronomical units). It takes Neptune 164 years to orbit the Sun. If it was located in 1846, then it has not yet made a full orbit since that time. But since Galileo inadvertently observed Neptune in 1613, it has already made two revolutions around the Sun since that time.

Neptune has 13 known moons. The most famous of these moons is Triton. According to Giles Sparrow in his book The Universe and How To See It,

Scientists think that Triton is a gatecrasher in the Neptune system which strayed into the giant’s gravitational reach, and was then pulled into a circular orbit around the planet. As Triton spiraled inward, it scattered most of Neptune’s original satellites, leaving just two significant survivors – Proteus and Nereid. The extreme gravitational forces may also have heated Triton up, melting its surface.

Triton also has a similar size, density, and chemical composition as Pluto. It could have been a binary before the gravity of Neptune pulled it in the planet’s orbit. Triton’s companion was expelled in the process. Triton has a retrograde orbit around Neptune, which means that its orbit is opposite to the rotation of the planet. (Wikipedia, 2007)

Triton has a density of 2.05 g/cm³, and is probably about 25% water ice, with the remainder being rocky material. It has a tenuous nitrogen atmosphere with small amounts of methane. Tritonian atmospheric pressure is only about 0.01 millibar. The surface temperature is at least 35.6  K (−237°C) because Triton's nitrogen ice is in the warmer, hexagonal beta crystalline state, and the phase transition between beta and cubic alpha nitrogen ice is that temperature. An upper limit in the low 40s can be set from vapor pressure equilibrium with nitrogen gas in Triton's atmosphere. This temperature range is colder than Pluto's average equilibrium temperature of 44 K (−229°C). Surprisingly, however, Triton is geologically active; its surface is fresh and sparsely cratered, and the Voyager 2 probe observed numerous icy volcanoes or geysers erupting liquid nitrogen, dust, or methane compounds from beneath the surface in plumes up to 8 km high. This volcanic activity is thought to be driven by seasonal heating from the Sun, unlike the tidal heating responsible for the volcanoes of Io. There are extensive ridges and valleys in complex patterns all over Triton's surface, probably the result of freezing/thawing cycles. [5] Triton's surface area is 23 million km² (4.5% of Earth, or 15.5% of Earth's land area.

http://en.wikipedia.org/wiki/Triton_(moon) June 20, 2007

Planetary Data- Neptune Visual magnitude (avg) Distance from the Sun     Length of year Rotation period Equatorial diameter   Mass (Earth = 1) Gravity at Equator (Earth = 1) Cloud-top temperature 7.8 2,795 million miles 4,498 million km 30.067 AU 164.9 Earth years 16.11 hours 30,775 miles 49,528 km 17.1 1.1   -330 °F -200 °C

PLUTO

          Pluto is no longer a planet. It is still there but it is no longer officially considered a planet, or maybe a regular planet. It has been ejected out of the planet club. I remember the time when its fate as a planet was being discussed by the International Astronomical Union. In the General Assembly of the International Astronomical Union held in Prague, Czech Republic in August, 2006, the IAU ruled that a planet “is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.” Apparently, Pluto would not qualify as a planet based on this definition, but it would qualify as a “dwarf planet.” What is a dwarf planet? According to the IAU’s, a dwarf planet is “a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.” Owen Gingerich, in his article The Inside Story of Pluto’s Demotion (Sky and Telescope, November, 2006), quotes Mark V. Sykes of the Planetary Science Institute that “The problem with this definition is that it is too simple and leads to nutty consequences”, such as Neptune losing its planet status because this giant planet has not yet cleared the dwarf Pluto from its neighbourhood. Gingerich asks: “What other silliness awaits?” from this definition?

          Well, I remember this period well. In the same General Assembly my nomination as Individual Member of the IAU was approved. Dr. Cynthia Celebre, the Chief of the Astronomy Research Section of PAGASA, who attended the assembly, announced through e-mail that my membership in said body was then “as good as approved”, the assurance coming from the Chairman of the IAU Executive Committee himself. Announcement of my official membership came via e-mail on September 15, 2006 by Karel Hucht, IAU General Secretary. I am only the fourth Individual Member from the Philipines, and Dr. Bernardo M. Soriano, Jr. Chief of the Atmospheric, Geophysical, and Space Sciences Bureau of PAGASA is about to retire this July, 2007. He told me he and his wife will be going to Canada. That’s going to be one man away. I hope Dr. Armando Lee and the rest of the present MS in Astronomy students of the RTU will finish their course soon. Philippine astronomy must have more good shepherds.

I would like to clarify “hydrostatic equilibrium”. Gingerich in his essay explains this:

In an astronomy textbook that I once adopted, Saturn was depicted floating in a bathtub, a vivid way to show that its average density is less than that of water. But one day a guest lecturer pointed out that it is physically impossible to build a bathtub big enough to hold Saturn – the tub’s own gravity would collapse it into a ball of porcelain and steel. That’s hydrostatic equilibrium! It applies to rocky bodies with masses exceeding about 0.1% of Earth’s mass and diameters about 800 kilometers or larger, and to icy ones about half that size.

Pluto is a system in its own right. Recently discovered are two small moons, Nix and Hydra.

Pluto has three known natural satellites: Charon, first identified in 1978 by astronomer James Christy; and two smaller moons, Nix and Hydra, both discovered in 2005.

The Plutonian moons are unusually close to Pluto, compared to other observed systems. Moons could potentially orbit Pluto up to 53% (or 69%, if retrograde) of the Hill sphere radius, the stable gravitational zone of Pluto's influence. For example, Psamathe orbits Neptune at 40% of the Hill radius. In the case of Pluto, only the inner 3% of the zone is known to be occupied by satellites. In the discoverers’ terms, the Plutonian system appears to be "highly compact and largely empty .

http://en.wikipedia.org/wiki/Image:Pluto_system_2006.jpg June 25, 2007

Pluto and its companions are in the Kuiper Belt, a region in the Solar System where small icy objects are plentiful. Astronomers estimate that there might be 100,000 Kuiper Belt Objects or KBOs. Is Pluto a KBO? Now, there are two big KBOs that we should be know. They are Quaoar and Eris and its moon Dysnomia.

 

Quaoar

No higher resolution available.

Quaoar was the first trans-Neptunian object to be measured directly from Hubble Space Telescope (HST) images, using a new, sophisticated method (see Brown’s pages for a non-technical description and his paper [4] for details). Given its distance Quaoar is on the limit of the HST resolution (40 milliarcseconds) and its image is consequently "smeared" on a few adjacent pixels. By comparing carefully this image with the images of stars in the background and using a sophisticated model of HST optics ( point spread function (PSF)), Brown and Trujillo were able to find the best fit disk's size which would give a similar blurred image. This method was recently applied by the same authors to measure the size of Eris.

However, these estimates only marginally agree with the recent (2007) infrared measurements by Spitzer Space Telescope suggesting a much larger albedo (0.19) and consequently a smaller diameter (844.4 +206.7 −189.6 km) [5 .

http://en.wikipedia.org/wiki/50000_Quaoar June 25, 2007

Eris and Dysnomia

Eris ( IPA: / ˈ ɛɹɪ s, ˈ ɪɹɪ s/ ), also designated 136199 Eris and formerly 2003 UB 313 (see minor planet names), is the largest known dwarf planet in the solar system and the ninth largest body orbiting the Sun directly. It is between 2,400 and 3,000 kilometres (1,490 to 1,860 miles) in diameter and 27% more massive than Pluto.

Eris was discovered in 2005 by a Mount Palomar-based team led by Mike Brown. It is a trans-Neptunian object (TNO) native to a region of space beyond the Kuiper belt known as the scattered disc. Eris has one moon, named Dysnomia; recent observations found no evidence of further satellites. With the exception of some comets, the pair are currently the most distant known objects in the Solar System.

Eris is classified as a dwarf planet and a scattered disk object (SDO). The latter is a category of the TNOs that are believed to have been "scattered" from the Kuiper belt into more distant and unusual orbits following gravitational interactions with Neptune as the solar system was forming. Although its high orbital inclination is unusual among the known SDOs, theoretical models suggest that objects that were originally near the inner edge of the Kuiper belt are scattered into orbits with higher inclinations than objects from the outer belt. [8] Inner-belt objects are expected to be generally more massive than outer-belt objects, and so astronomers expect to discover more large objects like Eris in high-inclination orbits.

As Eris is larger than Pluto, it was initially described as the " tenth planet" by NASA and in media reports of its discovery. [9] In response to the uncertainty over its status, and because of continuing debate over whether Pluto should be classified as a planet, the IAU delegated a group of astronomers to develop a new definition of the term planet. This definition was clarified under the new IAU definition of a planet, adopted on 24 August 2006. Eris has been termed a dwarf planet (a term distinct from "planet") by the IAU. [10] Brown has since stated his approval of the new "dwarf planet" label. [11] The IAU subsequently placed Eris into its Minor Planet Catalogue, giving it the designation (136199) Eris .

http://en.wikipedia.org/wiki/Eris_(dwarf_planet) June 25, 2007

 

Maran reminds us that KBOs are “beyond the reach of backyard telescopes, unless your backyard is on Neptune or on one of its moons.” About Pluto being a KBO, Maran wishes it “can be a a big KBO and a planet, too.” Here are additional facts about the KBOs:

The Kuiper Belt Objects

The Kuiper belt is similar to the asteroid belt, although it is far larger; at least 20 times as wide and and 200 times as massive. [3] [4] Like the asteroid belt, it consists mainly of small bodies (remenants from the Solar System's formation) and at least one dwarf planet. But while the asteroid belt is composed primarily of rock and metal, the Kuiper belt is composed largely of ices, such as methane, ammonia, and water.

The Kuiper belt is believed to be the repository for periodic comets, those, like Halley's Comet, with orbits lasting less than 200 years. The centaurs, comet-like bodies that orbit among the gas giants, are also believed to originate there, as are the scattered disc objects such as Eris; KBO-like bodies with massive orbits that take them as far as 100 AU from the Sun. Neptune's moon Triton is believed to be a captured KBO.

http://en.wikipedia.org/wiki/Kuiper_belt June 25, 2007

COMETS

          I have been fascinated by comets since I was in the elementary age. One of my most vivid recollections of that long-ago age was seeing a comet when I was in Grade 3 or 4. The comet was bright and clear with a tail. It was almost at the zenith at early evening and it was pointing downwards. The following day our teacher asked to draw a comet on the board. I drew what I just saw the night before, a small comet with not-so-prominent tail. My teacher nodded, then asked a classmate – I think his name was Arnel Pacleta, and he drew an outlandishly huge comet with what looked like boulders being ejected from the gigantic core. Arnel’s comet was as large as the width of the blackboard. My teacher applauded his efforts; mine was forgotten. But that did not stop me from looking at comets. I could already recognize naked-eye comets even then. When Halley’s comet returned in 1986, I drove my motorcycle to Mercedes Avenue in Pasig City, then a forlorn road surrounded by rice fields. I was not able to see Halley’s Comet because I did not know where to look. Later I learned that it had to be observed with instruments, not just by the naked eye. And then in 1997, some RTU employees visited the hometown of Dr. Rogelio Viana in Paluan, Occidental Mindoro. It was where I saw the Milky Way in all its glory. I pointed the Comet Hale-Bopp to Bobby Garcia when we were in the beach.

Comets have terrified mankind for centuries. Filipinos believe, like many peoples in the world, that comets are the messengers of disaster. William Shakespeare tells us that a comet presaged the death of King Henry V:

ung be the heavens with black, yield day to night! Comets, importing change of times and states, Brandish your crystal tresses in the sky, And with them scourge the bad revolting stars That have consented unto Henry's death! King Henry the Fifth, too famous to live long!

England ne'er lost a king of so much worth

But comets are more than harbingers of disasters. Stan Gibilisco in his book Astronomy Demystified warns that “A large comet smashing into the Earth would be, for the human race, the equivalent of a shark attack on an individual human being.” A chilling preview of what might happen to Earth in case of such impact was shown to us when the fragments of Comet Shoemaker-Levy repeatedly hit Jupiter in 1993, creating dark scars on the planet. But Gibilisco assures us that while this comet impact on Earth is certainly possible, “It is not necessary to loose sleep worrying about what is going to happen when the next major comet comes down.” Such an event is extremely rare, but we can’t say when it will happen. We are assured, however, according to Gibilisco, “that the time intervals between massive impacts are measured, on average, in tens of millions of years.”

There are billions of comets out there, beyond the orbit of Neptune. They mostly reside in the Kuiper Belt

Starting in 1992, astronomers have become aware of a vast population of small bodies orbiting the sun beyond Neptune. There are at least 70,000 "trans-Neptunians" with diameters larger than 100 km in the radial zone extending outwards from the orbit of Neptune (at 30 AU) to 50 AU. Observations show that the trans-Neptunians are mostly confined within a thick band around the ecliptic, leading to the realization that they occupy a ring or belt surrounding the sun. This ring is generally referred to as the Kuiper Belt. What is the Kuiper Belt?

The Kuiper Belt holds significance for the study of the planetary system on at least two levels. First, it is likely that the Kuiper Belt objects are extremely primitive remnants from the early accretional phases of the solar system. The inner, dense parts of the pre-planetary disk condensed into the major planets, probably within a few millions to tens of millions of years. The outer parts were less dense, and accretion progressed slowly. Evidently, a great many small objects were formed. Second, it is widely believed that the Kuiper Belt is the source of the short-period comets. It acts as a reservoir for these bodies in the same way that the Oort Cloud acts as a reservoir for the long-period comets.

http://www.ifa.hawaii.edu/faculty/jewitt/kb.html June 22,2007

One novel I read, and one of the greatest of them all, was Jules Verne’s Off on a Comet, a story of adventure aboard a comet. According o Gibilisco, “Comets are one of the greatest mysteries in astronomy” because there are a lot about it we still do not know. Comets are often at rest, serenely orbiting the Sun for millions of years, until they are disturbed from their orbit. This is explained to us by Giles Sparrow in his book The Universe and How to See It:

Most of the time, comets remain in deep-frozen sleep in outer space, but occasionally they are dislodged from their orbits and fall toward the inner Solar System. Comets arriving from the depths of the Solar System are still in the process of waking up and can be disappointingly unimpressive. The solid part of a comet, called the nucleus, is a lump of dirty ice, often just a few miles across, coated with a thin crust of dark, organic – carbon-based – chemicals that reflect sunlight poorly. As a result, comet nuclei are some of the darkest objects in the Solar System.

To find out what a comet nucleus really looks like, the Deep Impact project was launched in 2005.In this project a probe was sent crashing into the nucleus of Comet 9P/Tempel 1.

Arrows a and b point to large, smooth regions. The impact site is indicated by the third large arrow. Small grouped arrows highlight a scarp (a cliff or steep slope along the edge of a plateau) that is bright due to illumination angle. They show a smooth area to be elevated above the extremely rough terrain. The white scale bar in the lower right represents 1 km across the surface of the comet nucleus. The two directional arrows (vectors) in the upper right point to the Sun and Celestial North.

Photo Credit: NASA/UM M. F. A'Hearn et al., Science 310, 258 (2005); published online 8 September 2005 (10.1126/science.1118923). Reprinted with permission from AAAS

http://www.nasa.gov/mission_pages/deepimpact/multimedia/composite_map-20061002.html June 22,2007

As comets fall in past the orbit of Jupiter, the ice in the nucleus begins to melt and vaporize and streamers of gas burst into space. Gibilisco explains that “Ice exposed to sunlight quickly turns into gas, and soon the comet is surrounded by an expanding halo of gas – the coma. As the comet gets closer to the Sun, its coma increases in size and can develop into one or more tails stretching across millions of miles of space.”

The most famous comet of all time, the Comet Halley (which has a very interesting story itself), was welcomed by a fleet of spacecraft during its last approach in 1986. Look at the following image of the comet:

Giotto Mosaic of Halley's Comet

This image is a mosaic of 8 images taken by the Giotto spacecraft during the Halley encounter on March 13, 1986. The nucleus dimensions are about 16 by 8 by 8 kilometers. By examining the dust jets being emitted from the nucleus, scientists were able to determine that only about 10% of the surface was active. (Courtesy A. Tayfun Oner).

http://www.solarviews.com/eng/halley.htm June 22,2007

There are two types of comets we need to understand at this point. They are the short-period comets and the long-period comets:

A comet with a period of less than 200 years. Short-period comets are now subdivided into Jupiter-type comets, such as comets Encke and Tempel 2, which have periods of less than 20 years; and intermediate-period or Halley-type comets, with periods between 20 and 200 years. Jupiter-type comets are believed to originate in the Kuiper Belt, which surrounds the Sun at distances between about 30 astronomical units (the distance of Neptune) and 50 astronomical units (7.5 billion km, 4.7 billion miles). The gravitational influence of the outer planets, Neptune and Uranus, is thought occasionally to perturb some of the Kuiper Belt objects causing them to take up the orbits characteristic of comets in the Jupiter family. Halley-type comets, together with long-period comets, however, appear to come from the Oort Cloud.

http://www.daviddarling.info/encyclopedia/S/shortperiod.html June 22,2007

In late 2004 and early 2005, James Kevin Ty, the president of the Astronomical League of the Philippines, encouraged me to observe and sketch Comet Macholz. Look at this sketch, taken on January 11, 2005 at 60x in the Celestron 8-inch Schmidt-Cassegrain telescope:

THE MILKY WAY GALAXY

 

Has anybody of you seen the Milky Way Galaxy? I bet you haven’t. We live in an extremely light polluted urban area. The Milky Way is all but extinct in our place, or I mean we cannot see it anymore.

 

http://en.wikipedia.org/wiki/Milky_Way

 

When we were in Puerto Galera a few years ago, I brought with me my good old Astroscan, knowing the beauty of the night sky in Mindoro. There in the beach I have seen the elusive galaxy M101 in Ursa Major, whose surface brightness is very low. It has frustrated my search for it in my observing location in Taytay, Rizal, but I have seen it, while about to set, in Puerto Galera. It was at 3:30 in the morning. There were still people on the beach. I could hear laughter somewhere. It sounds like girls and boys chasing each other. Then, when I was looking at the jewels of Sagittarius, Dr. Dolores Tanawan, then the Dean of the College of Education and Dr. Carmel Mosura, then the Dean of the College of Business and Entrepreneurial Technology, suddenly came. They told me they heard I would be observing that morning so they joined me. The Milky Way was then like a white flowing robe draped across the southern sky, with all the folds and dark nebulae visible to the naked eye. I could hear in my mind Thomas Hardy’s description of it in his novel Two on a Tower, a story, according to Hardy, “to set the emotional history of two infinitesimal lives against the stupendous background of the stellar universe.” These were Swithin St. Cleeve, an astronomer, and his lover, Lady Constantine. Swithin explains to his lover:

…horrid monsters lie up there waiting to be discovered by any moderately penetrating mind… Impersonal monsters, namely, Immensities. Until a person has thought out the stars and their inter-spaces, he has hardly learnt that there are things much more terrible than monsters of shape, namely, monsters of magnitude without known shape. Such monsters are the voids and waste places of the sky. Look, for instance, at those pieces of darkness in the Milky Way…You see that dark opening in it near the Swan? There is still a more remarkable one south of the equator, called the Coal Sack, as a sort of nickname that has a farcical force from its very inadequacy. In these our sight plunges quite beyond any twinkler we have yet visited. Those are deep wells for the human mind to let itself down into, leave alone the human body! And think of the side caverns and secondary abysses to right and left as you pass on!

What shape is the Milky Way? Stephen Maran in his book Astronomy for Dummies explains the shape of the Milky Way with some delightful analogies:

The Milky Way is a spiral galaxy, consisting of a pizza-shaped formation of billions of stars (the galactic disk) that contains the spiral arms. The arms are shaped roughly like the streams of water from a rotating lawn sprinkler and contain lots of bright, young, blue and white stars and gas clouds. Groups of young, hot stars (called associations) dot the spiral arms in the galactic disk like pepperoni slices on a pizza. Bright and dark nebulae seem to mushroom in the arms as well. Between the arms are the interarm regions (not all astronomical terms are as catchy as Barnacle Bill, a rock on mars, or Red Rectangle, a nebula that’s actually shaped like an hourglass).

The centre of the Milky Way is in Sagittarius. It is the brightest portion of the Milky Way, only if you can see the galaxy with the naked eye. A few years back, I used to notice the brightening in Sagittarius where the centre is to be found during exceptionally clear nights on the RTU Pasig Campus Roof Deck, despite the light pollution. Now, the Pasig City General Hospital below Sagittarius has grown several storeys already and it killed the Milky Way. Anyway, not much of a Roof Deck remains in that campus nowadays… What is there to be found in the galactic centre? Maran explains:

Centered on the center is the galactic bulge, which would put a sumo wrestler to shame. The galactic bulge is a roughly spherical formation of millions of mostly orange and red stars, sitting like a great meatball at the center of the galactic disk and extending far above and below it. And at the center is Sagittarius A*, a supermassive black hole.

I was a little confused about the asterisk in that name. I know one Sagittarius A, but it has no asterisk, and it is a dwarf galaxy. So what is this asterisk thing? Let us find out from Wikipedia:

Sagittarius A* (pronounced "A-star", standard abbreviation Sgr A*) is a bright and very compact source of radio emission at the center of the Milky Way Galaxy, part of a larger astronomical feature at that location ( Sagittarius A). On October 16, 2002, an international team led by Rainer Schödel of the Max Planck Institute for Extraterrestrial Physics reported the observation of the motion of the star S2 near to Sagittarius A* for a period of ten years, and obtained evidence that Sagittarius A* is a highly massive compact object [2]. From examining the Keplerian orbit of S2, they determined the mass of Sagittarius A* to be 2.6 ± 0.2 million solar masses, confined in a volume with a radius no more than 17 light-hours (120 AU). Later observations [3] [4] determined the mass of the object to be about 3.7 million solar masses within a volume with radius no larger than 6.25 light-hours (45 AU).

This is compatible with, and strong evidence in support of, the hypothesis that Sagittarius A* is a supermassive black hole. While it is possible for the observed mass within the observed volume limit to be distributed among multiple objects, any such objects would undergo orbital collapse into a single black hole anyway within a few hundred years at most, a negligible amount of time compared with the lifetime of the galaxy.

 

 

Sgr A* (centre) and two light reflections from a recent explosion (circled)

http://en.wikipedia.org/wiki/Sagittarius_A* June 29, 2007

 

 

The Infrared Milky Way

This panoramic view encompasses the entire sky as seen by Two Micron All-Sky Survey. The measured brightnesses of half a billion stars (points) have been combined into colors representing three distinct wavelengths of infrared light: blue at 1.2 microns, green at 1.6 microns microns, and red at 2.2 microns. This image is centered on the core of our own Milky Way galaxy, toward the constellation of Sagittarius. The reddish stars seemingly hovering in the middle of the Milky Way's disc -- many of them never observed before -- trace the densest dust clouds in our galaxy. The two faint smudges seen in the lower right quadrant are our neighboring galaxies, the Small and Large Magellanic Clouds.

http://www.ipac.caltech.edu/2mass/gallery/showcase/allsky_stars/caption.html June 29, 2007

The estimates on the number of star in the Milky Way range from a low of 200 billion to a high of 400 billion. Most sources will tell us that the Milky Way is about 100,000 light years from end to end. The central bulge is about 10,000 light years across. The Sun lies in the galactic suburbs, not so far and not so near the centre. According to estimates, we are about 25,000 to 30,000 light years from the centre of the Galaxy.

The Galaxy is rotating around its centre. To complete one rotation takes 225 million years. This is called the galactic year. I wonder how long it would take us to go around the galactic bulge, so astronomers can see for themselves what is behind that bulge.

GALAXIES

          Perhaps the most challenging objects to observe in urban astronomy are the galaxies. I have observed and recorded quite a number of them using the Celestron 8-inch Schmidt-Cassegrain and the Orion 10-inch Newtonian reflector from the RTU Pasig Campus and from Montevista, Taytay, Rizal. There are lots of them in the region of Virgo, Coma Berenices, and Canes Venatici that could be observed with these telescopes. Observing galaxies, however, is a real challenge. You will have to wait for that perfect night when the transparency is excellent. You should time your observation when urban lights are at a minimum which means that you might have to wake up at 4 in the morning or even earlier to observe. I tell you I have done this so many times that I sometimes ask myself if there is anything wrong with me! But to see an elusive galaxy, to finally glimpse it in the eyepiece of the telescope after futile tries, would make you breathe easy and deep. My favorites are the edge-on galaxies. Many of them reveal some details about their structure. Some galaxies are unmistakably interacting, even through my modest telescopes. Some galaxies have the power to hypnotize an observer into silence, such as NGC 404 in Andromeda by its sheer beauty. Some galaxies could be mistaken for comets; some appear like globular clusters or planetary nebulae, but to see them will make you wonder how you are able to see objects millions of light years away.

The Milky Way galaxy has neighbors but it has also gobbled up a few nearby small galaxies. The Wikipedia lists the nearest galaxies to the Milky Way. I took just the nearest 25:

 

	Galaxy	Distance lightyears		Notes
1.	Milky Way Galaxy	0		Home galaxy of Earth
2.	Canis Major Dwarf Galaxy	25,000		Satellite of Milky Way
3.	Virgo Stellar Stream	30,000	[1]	Discovered October 2005
4.	Sagittarius Dwarf Elliptical Galaxy	81,000		Satellite of Milky Way
5.	Large Magellanic Cloud (LMC)	168,000		Satellite of Milky Way
6.	Small Magellanic Cloud (SMC)	200,000		Satellite of Milky Way
7.	Ursa Minor Dwarf Galaxy	240,000		Satellite of Milky Way
8.	Sculptor Dwarf Galaxy	254,000		Satellite of Milky Way
9.	Draco Dwarf Galaxy	280,000		Satellite of Milky Way
10.	Sextans Dwarf Galaxy	320,000		Satellite of Milky Way
11.	Ursa Major Dwarf	330,000		Satellite of Milky Way
12.	Carina Dwarf Galaxy	360,000		Satellite of Milky Way
13.	Fornax Dwarf Galaxy	460,000		Satellite of Milky Way
14.	Leo II Dwarf Galaxy	680,000	[2]
15.	Leo I Dwarf Galaxy	820,000	[2]
16.	Phoenix Dwarf Galaxy	1,300,000	[2]
17.	Barnard's Galaxy ( NGC 6822)	1,630,000	[2]
18.	NGC 185	2,010,000	[3]	Satellite of Andromeda
19.	Andromeda II	2,130,000	[3]	Satellite of Andromeda
20.	NGC 147	2,200,000	[3]	Satellite of Andromeda
21.	Leo A	2,250,000	[2]
22.	IC 1613	2,350,000	[2]
23.	Andromeda I	2,430,000	[3]	Satellite of Andromeda
24.	Andromeda III	2,440,000	[3]	Satellite of Andromeda
25.	Cetus Dwarf	2,460,000	[3]

http://en.wikipedia.org/wiki/List_of_nearest_galaxies July 2, 2007

To put order on the classes of galaxies, Edwin Hubble came up with a classification scheme which would put galaxies into definite categories, but even this might not cover all the types of galaxies out there, so he just lumped out those which do not belong to any particular group into “Irregular Galaxies”. Here is an additional explanation from the Wikipedia (2007):

After the elliptical galaxies the diagram splits into two branches. The upper branch covers spiral galaxies. It starts off with S0, also called lenticular galaxies. The "S" means spiral, the "0" means no arms, and the subscript number indicates how heavily a stripe is absorbed out of the image of the galaxy by dust in the galactic disc. On the same branch are the next 3 types which all have spiral arms. The "S" here also means spiral, but the lower case letter after it tell how wound up the arms are. They range from "a" to "d" having the following meanings:

Sa - tightly-wound, smooth arms, and a bright central disc

Sb - better defined spiral arms than Sa

Sc - much more loosely wound spiral arms than Sb

Sd - very loose arms, most of the luminosity is in the arms and not the disc

The lower branch of the diagram covers barred spiral galaxies given the symbol "SB". This branch starts with SBO galaxies which is followed by a subscript number that indicates how heavily defined the bar is. After that the branch continues with the SB galaxies which have lower case letters after them that indicates how heavily defined the bar is. They range from "a" to "c" having the following meanings:

SBa - a bright center and tight spirals

SBb - better defined arms than SBa galaxy and are more loosely wound

SBc - even looser arms, and a much dimmer central portion of the galaxy

http://en.wikipedia.org/wiki/Galaxy_morphological_classification June 29, 2007

 

Spiral

Spiral galaxies usually consist of two major components: A flat, large disk which often contains a lot of interstellar matter (visible sometimes as reddish diffuse emission nebulae, or as dark dust clouds) and young (open) star clusters and associations, which have emerged from them (recognizable from the bluish light of their hottest, short-living, most massive stars), often arranged in conspicuous and striking spiral patterns and/or bar structures, and an ellipsoidally formed bulge component, consisting of an old stellar population without interstellar matter, and often associated with globular clusters. The young stars in the disk are classified as stellar population I, the old bulge stars as population II. The luminosity and mass relation of these components seem to vary in a wide range, giving rise to a classification scheme. The pattern structures in the disk are most probably transient phenomena only, caused by gravitational interaction with neighboring galaxies.

Lenticular (S0)

These are, in short, "spiral galaxies without spiral structure", i.e. smooth disk galaxies, where stellar formation
has stopped long ago, because the interstellar matter was used up. Therefore, they consist of old population II
stars only, or at least chiefly. From their appearance and stellar contents, they can often hardly be distinguished
from ellipticals observationally.

Elliptical

Elliptical

Elliptical galaxies are actually of ellipsoidal shape, and it is now quite safe from observation that they are usually triaxial (cosmic footballs, as Paul Murdin, David Allen, and David Malin put it). They have little or no global angular momentum, i.e. do not rotate as a whole (of course, the stars still orbit the centers of these galaxies, but the orbits are statistically oriented so that only little net orbital angular momentum sums up). Normally, elliptical galaxies contain very little or no interstellar matter, and consist of old population II stars only: They appear like luminous bulges of spirals, without a disk component.

However, for some ellipticals, small disk components have been discovered, so that they may be representatives of one end of a common scheme of galaxy forms, which includes the disk galaxies.

 

Irregular

Often due to distortion by the gravitation of their intergalactic neighbors, these galaxies do not fit well into the scheme of disks and ellipsoids, but exhibit peculiar shapes. A subclass of distorted disks is however frequently occurring .

http://www.seds.org/messier/galaxy.html June 28, 2007

How did galaxies get that way?

• The simplest explanation is that
• If all the gas is made into stars before the gas has time to form a disk, then you get an elliptical galaxy.
• If the gas has time to stabilize into a disk before it is all used up, then you get a spiral galaxy.
• Or perhaps some of the elliptical galaxies are made from merging of other types of galaxies.
• Observations of distant galaxies indicate that spiral galaxies were more common in the past than they are today.
• So maybe yesterday's spirals are today’s ellipticals.
• This is an active research area. One problem is that if most of the mass in galaxies is unaccounted for, we have a hard time understanding the dynamics of galaxy formation.

http://zebu.uoregon.edu/~soper/Galaxies/types.html June 28, 2007

What are Active Galactic Nuclei (AGN)?

During one of the meetings of the Philippine Astronomical Society held here in my office, a guest lecturer showed a
picture of M87 projected on the wall. I asked if anybody knew what that beam of light or jet shooting out of the
galaxy is, but nobody could give an answer, so I just searched for M87 in the Internet. Here is what we have found:

In some galaxies, known as "active galactic nuclei" (AGN), the nucleus (or central core) produces more radiation than the entire rest of the galaxy! Quasars are very distant AGN - the most distant quasars mark an epoch when the universe was less than a billion years old and a sixth of its current size. In some cases, the size of the AGN is smaller than the size of our solar system. Current theory suggests that there is a supermassive black hole (millions of times the mass of the sun) at the center of AGN.

 

Messier 87

In 1918 Lick Observatory astronomer Heber Curtis discovered a jet of matter coming from M87 which he described as "a curious straight ray". This jet extends at least 5000 light-years from the nucleus of M87 and is made up of matter ejected from the galaxy, most likely by a black hole (a fact made more likely by the discovery of a disk of rapidly rotating gas around the nucleus of M87). Astronomers believe that the black hole in this galaxy has a mass of approximately 3 billion (3×10 9) solar masses. M87 has also been found to be a strong source of X-rays. Its proximity means that it is one of the best studied radio galaxies

http://en.wikipedia.org/wiki/Elliptical_Galaxy_M87 July 2, 2007

I would like to recommend my own list of great galaxies. There are so many but I will limit the list to just about 10:

NGC 4565, a long and big edge-on galaxy. A dark lane bisects the galaxy almost in the middle. You will have to wait for a clear and transparent morning to view this one satisfactorily, except if you are observing in a really dark location.

NGC 404, my choice of the most beautiful galaxy in the Universe. It is not astoundingly beautiful. Its beauty is in it simplicity, a beauty that calms, like the slow fire in a fireplace that comforts.

NGC 55, even through light pollution, this huge edge-on galaxy can be visible, and I wonder how it would look like from a dark observing spot.

NGC 5102, it is in the same medium-power field as Iota Centauri. The core of the galaxy is very bright, and not even the yellow glow of the nearby Iota could extinguish the halo.

M82, an irregular galaxy that shows many details even in urban astronomy.

M104, the dark lane bisecting the bottom of the galaxy really makes the galaxy look like a hat.

M64, you will recognize this galaxy in the mirror when you wake up with too little sleep. Your eyes will look like it has a blackeye and that is how this galaxy looks like.

NGC 4038 and NGC 4039, two interacting galaxies. It is hard to see the lane bridging the two galaxies but you will have a glimpse that they are merging.

NGC 4945, an elusive galaxy that materialized like a ghost after not a few tries. You might have to wait for the perfect night to see this one.

Following are some of the galaxy images taken by John Nassr of the Philippine Astronomical Society and the Astronomical League of the Philippines. To view these images in better light, please try the website.

 

http://tech.ph.groups.yahoo.com/group/philastrosociety/photos/view/ab00?b=27&m=f&o=0 July 2, 2007

ngc1097 AP127 f5.3 ATK1HR LRGB 135,30,30,40min - Nassr

By: jnassr2000

http://tech.ph.groups.yahoo.com/group/philastrosociety/photos/view/ab00?b=40&m=f&o=0

July 2, 2007

ngc1532 AP127 f5.3 ATK1HR LRGB 90,20,20,30min 5min subs - Nass

By: jnassr2000

http://tech.ph.groups.yahoo.com/group/philastrosociety/photos/view/ab00?b=41&m=f&o=0 July 2, 2007

M104 Vir AP127 f8 ATK16HR LRGB 120,60,60,20min 10 min subs - Na

By: jnassr2000

http://tech.ph.groups.yahoo.com/group/philastrosociety/photos/view/ab00?b=80&m=f&o=0 July 2, 2007

Some of the most fascinating galaxies are the interacting galaxies. Somehow the Universe is not big enough for them that they have to collide with one another. Here are some additional explanation:

Interacting galaxies (Colliding galaxies) is the result of one galaxy's gravity disturbing another galaxy. An example of minor interaction would be a satellite galaxy disturbing the primary galaxy's spiral arms. An example of major interaction would be a galactic collision.

 

An artist's impression of interacting galaxies

 Satellite interaction

A giant galaxy interacting with its satellites is common. A satellite's gravity could attract one of the primary's spiral arms. Or even the satellite could dive in to the primary (e.g. Sagittarius Dwarf Elliptical Galaxy). This could trigger a small amount of star formation. The satellite could be a vacuum cleaner and suck up some of its primary's stars or vice versa .

 

The Whirlpool Galaxy with its satelliteNGC 5195

Galaxy collision

Colliding galaxies are common in galaxy evolution. Colliding may lead to merging. Merging is the most violent of all galaxy interactions. This occurs when two galaxies collide and do not have enough momentum to continue traveling after the collision. Instead, they fall back into each other and eventually merge together, forming one galaxy. If one of the colliding galaxies is much larger than the other, it will remain largely intact after the merger; that is, the larger galaxy will look much the same while the smaller galaxy will be stripped apart and become part of the larger galaxy. Collisions are less violent than mergers in that both galaxies remain separate after the collisions.

 

 

The Mice Galaxies

 

Galactic cannibalism

Galactic cannibalism refers to the process by which a large galaxy, through tidal gravitational interactions with a companion, merges with that companion, resulting in a larger, often irregular galaxy.

The most common result of the gravitational merger of two or more galaxies is an irregular galaxy of one form or another, although elliptical galaxies may also result. It has been suggested that galactic cannibalism is currently occurring between the Milky Way and the Large and Small Magellanic Clouds. Streams of gravitationally-attracted hydrogen arcing from these dwarf galaxies to the Milky Way is taken as evidence for this theory.

 

Name	Type	Distance (million ly)	Magnitude	Notes
Whirlpool Galaxy (M51)	SAc (SB0-a)	37	+8.4	Satellite interacting with its primary
NGC 2207 and IC 2163	SAc/SAbc	114	+11	galaxies going through the first phase in galactic collision
Mice Galaxies (IC 819/20)	S0/SB(s)ab	300	+13.5	galaxies going through the second phase in galactic collision
NGC 1097	SB(s)bc (E6)	45	+9.5	Satellite interacting with its primary
Antennae Galaxies (NGC 4038/9)	SAc/SBm	68	+10.3	galaxies going through the third phase in galactic collision
NGC 520	S	100	+11.3	galaxies going through the third phase in galactic collision

http://en.wikipedia.org/wiki/Interacting_galaxy July 2, 2007

Interacting Galaxies

An 'interacting galaxy' is one that is in the process of being affected by another galaxy. This is not an uncommon occurrence as galaxies are rarely found in isolation. Most are surrounded by a swarm of satellite galaxies and are themselves embedded in larger aggregates called groups or clusters.

Interactions can disturb, or even radically change, the morphologies of the galaxies involved, often inducing new bursts of star formation. The most common interaction is known as a 'fly-by' and involves two or more galaxies (which do not actually come into contact) approaching close enough that the gravitational field of each galaxy influences the gravitational fields of the others. These high speed encounters can create new structures such as warps or bars, or even tidal tails that extend well beyond the main body of the galaxy.

A spectacular example of a multiple interaction is the Messier 81 group of galaxies. The left-hand panel shows the optical view of M81 (the large dominant galaxy) with neighbouring galaxies NGC 3034 (above) and NGC 3077 (lower left). The right-hand panel shows the HI (radio) image which traces the distribution of cold gas in the system. This reveals long tidal tails of gas, not seen in the optical image, which connect the galaxies - a clear indication that all three galaxies are interacting with each other.

 

The Cartwheel galaxy has recently suffered an interaction, probably when one of the two galaxies to the right ploughed through its centre.
Credit: Kirk Borne (STScI), and NASA

 

 

 

A satellite galaxy is 'shredded' by its parent galaxy.
Credit: Duncan Forbes and Mike Beasley (Swinburne).

http://cosmos.swin.edu.au/entries/interactinggalaxies/interactinggalaxies.html?e=1 July 2, 2007

Now, the Milky Way Galaxy is part of the Local Group of galaxies which include the Andromeda Galaxy and its satellite galaxies M32 and M110. The members of the Local Group are about 30 and are gravitationally bound to each other.

Further out in the Universe there are other clusters of galaxies, some are rich clusters, like the Virgo Supercluster which has about a thousand members while others have few members. According to Stephen Maran in his book Astronomy for Dummies, “the biggest superclusters, or groups of superclusters, are called Great Walls.”

The Milky Way system is a spiral galaxy consisting of over
400 billion stars, plus gas and dust arranged into three general components as shown to the left:

• The halo - a roughly spherical distribution which contains the oldest stars in the Galaxy,
• The nuclear bulge and Galactic Center.
• The disk, which contains the majority of the stars, including the sun, and virtually all of the gas and dust

http://casswww.ucsd.edu/public/tutorial/MW.html

 

 

Radio image of the central region of the Milky Way

The Center of the Galaxy

What lies at the center of our Galaxy? Again, dust obscures the visible light from us and we must use radio and infrared observations to elicit the nuclear properties of the Galaxy. A census shows us that the Galactic Center region is an unusually crowded place, even in this visible-light Map of Central region. At radio wavelengths, where we can peer down to the very center, we see the complex strctures shown in the 1-meter wavelength radio map made by NRL astronomers which is shown below. The map shows a region about 2000 light-years on a side; the center of the Milky Way coincides with the source marked Sag A (or Sagittarius A), which is actually three sources, a yound supernova remnant on the east side, an unusual ionized hydrogen region on the west side, and a very compact source called Sagittarius A* at the very center.

http://casswww.ucsd.edu/public/tutorial/MW.html

THE DOPPLER EFFECT

We have experienced being waken up in the middle of the night by a fire truck with loud siren rushing toward a fire somewhere. When the truck is approaching the sound of its siren steadily increases in loudness. The loudest sound is when the truck is nearest where you are sleeping then the sound steadily diminishes as the truck moves away. This is the Doppler effect at work. According to the Philip’s Astronomy Dictionary, Doppler effect means “The apparent increase in frequency (and decrease in wavelength) of radiation from source moving towards the observer, or the similar increase in frequency (increase in wavelength) of radiation from a source moving away.” The Firefly Encyclopedia of Astronomy explains it this way: “If a source is approaching, the frequency of the radiation is increased (more wave crests per second reach the observer than would be the case if the source were stationary relative to that observer) and its observed wavelength decreased. If the source is receding, the frequency is decreased and the wavelength is increased.”

Understanding the Doppler effect is important to astronomers. In astronomy, if the source is moving towards us, like the Andromeda Galaxy, its spectral lines are shifted towards the blue end of the spectrum. We call this the blueshift. But if the object is moving away from us, the spectral lines shift towards the red. We call this the redshift. According to the Firefly Encyclopedia of Astronomy,

The velocity of a light source along the line of sight (the so-called ‘radial velocity’) may be determined by comparing the observed wavelengths of its spectral lines with the wavelengths that those lines would have if the source were stationary. The measured velocity, v, is negative if the source is approaching the observer, or positive if it is receding .

                                                                                            The Brightest Stars

           Below you find a list of the brightest stars in the sky (up to 2.5 mag). The asterisk at the spectral type of some stars indicates that it is a binary; the spectral type of the brighter component has been listed.
An asterisk at the spectral type of some stars means that they are variables; it is interesting to note that many of these stars are double or even multiple stars.
The brightness has been adopted from the Bright Star Catalog, Rev 4. The radii (in solar units) were taken from the Catalogue of Apparent Diameters and Absolute Radii of Stars.
I suggest your class should observe as many of these stars as possible using telescopes. Carefully take note of the telescope used, the magnification, the sky condition and the time of observation, and if possible, you may sketch what you see.

M: Apparent Magnitude D: Distance (in light years) R: Radius (solar units)

(From: http://www.seds.org/Maps/Stars_en/)

 

HD #	Star	Name	M	RA	Dec	SpecT	D	R
48915	alpha CMa	Sirius	-1.46	06 45 8.9	-16 42 58	A1 V*	8.6	1.7
45348	alpha Car	Canopus	-0.72	06 23 57.2	-52 41 44	F0II	74	?
128620	alpha Cen	Rigil Kent	-0.01	14 39 36.2	-60 50 07	G2V+K1V	4.3	1.18
124897	alpha Boo	Arcturus	-0.04	14 15 39.6	+19 10 57	K1IIIbCN-1	34	25.1
172167	alpha Lyr	Vega	0.03	18 36 56.2	+38 47 01	A0V	25.3	2
34029	alpha Aur	Capella	0.08	05 16 41.3	+45 59 53	G8	41	13
34085	beta Ori	Rigel	0.12	05 14 32.2	-08 12 06	B8 I*	815	63
61421	alpha CMi	Procyon	0.38	07 39 18.1	+05 13 30	F5 IV	11.4	2
10144	alpha Eri	Archenar	0.46	01 37 42.9	-57 14 12	B3Vpe	69	5.0
39801	alpha Ori	Beteigeuse	0.50	05 55 10.3	+07 24 25	M2 I	650	226
122451	beta Cen	Hadar	0.61	14 03 49.4	-60 22 22	B1III	320
187642	alpha Aql	Altair	0.77	19 50 46.9	+08 52.6	A7V	16.8	1.6
213468			0.77			A0V		2.19
29139	alpha Tau	Aldebaran	0.85	04 35 55.2	+16 30 33	K5 III	60	46
116658	alpha Vir	Spica	0.98	13 25 11.5	-11 09 41	B1 III + B2 V	220	6.6
148478	alpha Sco	Antares	0.96	16 29 24.4	-26 25 25	M1.5I*	425	510
62509	beta Gem	Pollux	1.14	07 45 18.9	+28 01 34	K0 III	40	10
216956	alpha PsA	Fomalhaut	1.16	22 57 39.0	-29 37 20	A3Va	22	1.5
197345	alpha Cyg	Deneb	1.25	20 41 25.8	+45 16 49	A2Iae	1630	?
111123	beta Cru	Mimosa	1.25	12 47 43.3	-59 41 19	B0.5III	460
87901	alpha Leo	Regulus	1.35	10 08 22.3	+11 58 02	B7V*	69	3.5
168740			1.36			A2		1.8
52089	epsilon CMa	Adhara	1.50	06 58 37.5	-28 58 20	B2II	570	?
108248	alpha Cru	Acrux	1.58	12 26 35.9	-63 05 56	B1*	510
60178	alpha Gem	Castor	1.58	07 34 35.9	+31 53 18	A1V*	46	1.7
108903	gamma Cru	Gacrux	1.63	12 31 09.9	-57 06 47	M3.5III	120
158926	lambda Sco	Shaula	1.63	17 33 36.4	-37 06 13	B1.5IV	325	6.6
35468	gamma Ori	Bellatrix	1.64	05 25 07.8	+06 20 59	B2III	303	8.1
35497	beta Tau	El Nath	1.65	05 26 17.5	+28 36 27	B7 III	130	5.2
80007	beta Car	Miaplacidus	1.68	09 13 12.1	-69 43 02	A2IV		2.6
37128	epsilon Ori	Alnilam	1.70	05 36 12.7	-01 12 07	B0Iae		31
209952	alpha Gru	Al Na'ir	1.74	22 08 13.9	-46 57 40	B7IV	91	3.6
112185	epsilon UMa	Alioth	1.77	12 54 01.7	+55 57 35	A0pCr	49	3
68273	gamma Vel	Regor	1.78	08 09 31.9	-47 20 12	WC8+O7.5e		17
20902	alpha Per	Marfak (Algenib)	1.79	03 24 19.3	+49 51 41	F5Ib	270	55
95689	alpha UMa	Dubhe	1.79	11 03 43.6	+61 45 03	K0IIIa	105	?
54605	delta CMa	Al Wazor	1.84	07 08 23.4	-26 23 35	F8Ia	650	300 (?)
169022	epsilon Sgr	Kaus Australis	1.85	18 24 10.3	-34 23 05	B9.5III	160
71129	epsilon Car	She (Avior)	1.86	08 22 30.8	-59 30 34	K0II*	330	70
120315	eta UMa	Benetnasch (Alkaid)	1.86	13 47 32.3	+49 18 48	B3V		3.9
159532	theta Sco	Sargas	1.87	17 37 19.0	-42 59 52	F1II	140	40
40183	beta Aur	Menkalinam	1.90	05 59 31.7	+44 56 51	A2IV	84	2.5
150708	alpha TrA	Ras al Muthallath (Atria)	1.92	16 48 39.9	-69 01 40	K2 II	130	37
47105	gamma Gem	Almisan (Alhena)	1.93	06 37 42.7	+16 23 57	A0IV	78	3
193924	alpha Pav	Joo Tseo (Peacock)	1.94	20 25 38.8	-56 44 07	B2IV	160	5
74956	delta Vel	Koo She	1.96	08 44 42.2	-54 42 30	A1 V	70	1.89
44743	beta CMa	Murzim	1.98	06 22 41.9	-17 57 22	B1II-II	300	9
81797	alpha Hya	Alphard	1.98	09 27 35.2	-08 39 31	K3III	200	37
12929	alpha Ari	Hamal	2.00	02 07 10.3	+23 27 45	K2IIIabCa-I	74	21.4
	T CrB		2.00	15 59 30.1	25 55 13	sdBe+gM3+Q
8890	alpha UMi	Polaris	2.02	02 31 50.5	+89 15 51	F7:Ib-IIv	470	19.5
15191 ? 175224	sigma Sgr	Nunki	2.02	18 55 15.8	-26 17 48	B2.5V	160	4.5
4128	beta Cet	Deneb Kaitos (Diphda)	2.04	00 43 35.3	-17 59 12	K0III	57	14
37742	zeta1 Ori	Alnitak	2.05	05 40 45.5	-01 56 34	O9.5Ibe*	400	20
358	alpha And	Alpheratz (Sirrah)	2.06	00 08 23.2	+29 05 26	B8IVpMnHg	120	3.6
6860	beta And	Mirach	2.06	01 09 43.9	+35 37 14	M0IIIa	76	21.8
12533	gamma1 And	Alamach	2.06	02 03 53.9	+42 19 47	K3-IIb*	400	83.2
123139	theta Cen	Haratan (Menkent)	2.06	14 06 40.8	-36 22 12	K0IIIb	56	8.9
38771	kappa Ori	Saiph	2.06	05 47 45.3	-09 40 11	B0.5Iav	550	38
159561	alpha Oph	Ras Alhague	2.08	17 34 56.0	+12 33 36	A5III	67	3.15
131873	beta UMi	Kochab	2.08	14 50 42.2	+74 09 20	K4 III	120	37
214952/td>	beta Gru	Al Dhanab	2.10	22 42 40.0	-46 53 05	M5III	270
19356	beta Per	Algol	2.12	03 08 10.1	+40 57 21	B8V	100	3.16
102647	beta Leo	Denebola	2.14	11 49 03.5	+14 34 19	A3V	42	1.8
110304	gamma Cen	Koo Low	2.17	12 41 30.9	-48 57 34	A1IV	130
194093	gamma Cyg	Sadr	2.20	20 22 13.6	+40 15 24	F8Ib	470	30.9
78647	lambda Vel	Suhail	2.21	09 07 59.7	-43 25 12	K4 Ib-II	220
3712	alpha Cas	Schedir	2.23	00 40 30.4	+56 32 15	K0IIIa	230	40.7
139006	alpha CrB	Alphecca (Gemma)	2.23	15 34 41.2	+26 42 53	A0V	67	2.7
164058	gamma Dra	Etamin	2.23	17 56 36.3	+51 29 20	K5III	148	23.6
36486	delta Ori	Mintaka	2.23	05 32 00.3	-00 17 57	B0*	600	16
432	beta Cas	Caph	2.25	00 09 10.6	+59 08 59	F2III	45	2.0
80404	iota Car	Tureis (Aspidiske)	2.25	09 17 05.4	-59 16 31	A8Ib	???	192
66811	zeta Pup	Suhail Hadar (Naos)	2.25	08 03 35.0	-40 00 11	O5Iaf	800	16
116656	zeta UMa	Mizar	2.27	13 23 55.5	+54 55 31	A2VpSrSi*	190	1.6
151680	epsilon Sco	Wei	2.29	16 50 09.7	-34 17 36	K2.5III	69	16
129078	alpha Lup		2.30	14 41 55.7	-47 23 17	B1.5III	130
118716	epsilon Cen		2.30	13 39 53.2	-53 27 59	B1III
	eta Cen		2.31	14 35 30.3	-42 09 28	B1.5Vne
133275 ? 143275	delta Sco	Dschubba	2.32	16 00 19.9	-22 37 18	B0.3IV		?
95418	beta UMa	Merak	2.37	11 01 50.4	+56 22 56	A0V	76	2.5
2261	alpha Phe	Ankaa	2.39	00 26 17.0	-42 18 22	K0III	76 10.2
206778	epsilon Peg		2.39	21 44 11.1	+09 52 30	K2Ib		26.5
160613	kappa Sco		2.41	17 42 29.1	-39 01 48	B1.5III		6.9
217906	beta Peg	Scheat	2.42	23 03 46.4	+28 04 58	M2.5II-III		38.7
203280	alpha Cep	Alderamin	2.44	21 18 34.7	62 35 08	A7V	49	2
103287	gamma UMa	Phecda	2.44	11 53 49.8	+53 41 41	A0Ve	88	2.4
58350	eta CMa	Aludra	2.45	07 24 5.6	-29 18 11	B5Ia	270	60
197989	epsilon Cyg		2.46	20 46 12.6	+33 58 13	K0III		13.2
5394	gamma Cas	Cih	var. (2.47)	00 56 42.4	+60 43 00	B0IVe	200	23
218045	alpha Peg	Markab	2.49	23 04 45.6	+15 12 19	B9V		2
81188	kappa Vel	Cih	2.50	09 22 06.8	+55 00 38	B2 IV		6.9

STAR COLORS

When I show my students the stars through a telescope I ask them about the color of the stars. Almost all of them are surprised to see that star have colors. They thought stars are just plain white until they see the red-orange Betelgeuse, the bluish-white Sirius, the orange Aldebaran, and the yellowish Capella.

Why do stars have different colors? Giles Sparrow explains in his book The Universe and How To See It:

Stars have distinct colors created by the combination of different frequencies of light. White light is not a color but is a combination of all colors, from deep red to violet. Our Sun produces light that comes close to white, but and absence of blue light gives it a slight reddish-yellow bias.

        Like in a stove, the fuel, such as wood, that gives yellow light is cooler than blue flame fueled by liquefied petroleum gas or LPG. So is it with stars. Blue stars are hotter than red stars. According to Sparrow,

        Different colors of light are produced by stars of different temperatures – as the temperature rises the frequency of light emitted increases, shifting the color of the star toward the blue end of the visible spectrum. With more heat, the radiation emitted shifts into the ultraviolet, and beyond to X rays and gamma rays, all of which are invisible to human eyes. Conversely, objects too cool to glow visible emit invisible infrared radiation, or low-frequency radio waves.

Can you see green stars out there?

WOBAFGKMRNS

          The letters at the bottom of the H-R Diagram are the spectral types of the stars. The letters go from the hottest stars to the coolest ones, so W stars are the hottest and the S stars are the coolest. Astronomers found a way for their students to memorize these spectral types easily. Just remember “Wow! O Be A Fine Girl Kiss Me Right Now Sweetie!”

          The very hottest stars are the Wolf-Rayet stars which have surface temperatures as high as 80,000 degrees C. If you can observe in the constellation Vela, look for Gamma Velorum. Gamma Velorum is a beautiful sight to behold in a telescope. It is a three-star system, with the brightest at magnitude 1.88 and blazing blue. The companion is magnitude 4.5 and also very brilliant, while the third member is quite dim at magnitude 8.5. Patrick Moore in his book Atlas of the Universe explains that WR stars are “ejecting material at an amazing rate” like super profligate spendthrifts, the Prodigal Son among the stars. Gamma Velorum is fated not to live for so long with its lifestyle. It is fated to die a violent death, to explode into a supernova. It has only a few more million years to live, so you better see it now before it is gone.

          According to Patrick Moore, the spectra of WR stars “show many bright emission lines, and they are unstable, with expanding shells moving outward at up to 3,000 kilometers (over 1,800 miles) per second.”

          Some stars at the opposite ends of the H-R Diagram are either too hot or too cold. Patrick Moore explains the properties of S Doradus, a star in the nearby galaxy The Large Magellanic Cloud, and Eta Carinae;

          Some supergiants are powerful by any standards; S Doradus…is at least a million times as luminous as the Sun, though it is too far away to be seen with the naked eye. Even more powerful is the strange, erratic variable Eta Carinae, which may equal 6 million Suns and has a peculiar spectrum which cannot be put into any regular type.

          On the other end of the H-R Diagram Moore explains some of the properties of MH 18: “On the other hand a dim star known as MH 18, identified in 1990 by M.H. Hawkins at the Royal Observatory Edinburgh, has only 1/20,000 the luminosity of the Sun.”

          The main categories WOBAFGKMRNS are subdivided into sub-categories from 0 to 9. Thus, a star can be classified as A9 or M0. A G9 star is followed by a K0 star. The following table is from Patrick Moore’s Atlas of the Universe. The table gives a brief description of each spectral type:

Stellar Spectra

Type	Spectrum	Surface Temperature	Example
W	Many bright lines. Divided into WN (nitrogen sequence). Rare.	Up to 80,000	γVelorum (WC7)
O	Both bright and dark lines. Rare	40,000-35,000	Ζ Orionis (09.5)
B	Bluish white. Prominent lines.	25,000-12,000	Spica, β Crucis
A	White. Prominent hydrogen lines.	10,000-8000	Sirius,Vega
F	White or over slightly yellowish. Calcium lines very prominent	7500-6000	Canopus , Polaris
G	Yellowish: weaker hydrogen lines, many metallic lines.	Giants 5500-4200 Dwarfs 6000-5000	Capella, Sun
K	Orange . Strong metallic lines.	Giants 4000-3000 Dwarfs 5000-4000	Arcturus, Aldebaran Ε Eridani, τCeti
M	Orange-red. Complicated spectra, with many bands due to molecules.	Giants 3400   Dwarfs 3000	Betelguex, Antares Proxima Centuri
R	Reddish	2600	T Lyrae
N	Reddish; Strong carbon lines	2500	R Leporis
S	Red; prominent bands of titanium oxide and zirconium oxide	2600	χ Cygni, R Cygni

          Our Sun is a type G2 star. Rigel is a very massive and luminous star. It is 60,000 times as luminous as the Sun, is white, and with a temperature of more than 12,000 degrees C. Have you seen Sirius B in the telescope? It’s about time you did. Ask your professor to show it to you! Sirius B is a white dwarf which has used up all its nuclear fuel. It has a diameter of only 40,000 km, even smaller than Uranus but it is extremely dense and as massive as the Sun! It has been estimated that one ton of material from Sirius B would fit in a matchbox!

THE FIXED STARS ARE NOT SO FIXED

          They are not so fixed because they are moving all the time.

          Apparently, the stars are in constant motion because the whole sky rotates overhead because the earth is turning. When you look at a star through a telescope without a motor drive, you will see that after a few moments, whether you use low or high power, the star will no longer in the field of view, and you will tell your instructor “Sir, nawala na!” so the instructor will make the adjustments to bring it back into view.

          I was asked not a few times about those star-like objects that really move in the sky. All the time those objects were artificial satellites going through their pre-arranged travel paths through the sky. The stars, as we can see, move, but we cannot really detect the movement through the naked eye; it is not that the Big Dipper stars will move and relocate to the southern sky, or the stars in the Tatlong Maria in Orion will rearrange themselves into a triangle in a single night!

          The stars are so far away so we cannot detect their movement, but if can go near them, we will see that they move really very fast, in hundreds of miles per second. The Big Dipper stars will have rearranged themselves in 20 thousand years. Even the Andromeda Galaxy is moving, and it is moving towards us! Bob Berman in his book Secrets of the Night Sky explains:

          It’s a safe bet that intelligent life gazes upward from numerous Andromedan planets, curious about our smudgy galaxy floating in their sky. If only one planetary system in a billion contains creatures with intelligence, then thousands of such worlds are hidden in the silky folds of Andromeda’s spirals. Perhaps they even realize, as we do, that our two galaxies are approaching each other. With the separation decreasing by nearly 50 miles each second, there’s reasonable chance we will collide in 4 to 6 billion years…offering us the attractive prospect that we may someday switch allegiance and join Andromeda.

                                                                 THE HERTZSPRUNG-RUSSELL DIAGRAM

The Hertzsprung-Russell Diagram is actually a graph where astronomers plot the spectral type of a star with its absolute magnitude.

The vertical axis on the left plots the absolute magnitude of stars. The brightest absolute magnitude is towards the top of the line, while the dimmest absolute magnitude is towards the bottom.

The horizontal axis refers to the temperature of the stars. The highest temperature is towards the left of the line while the coolest is toward the right.

THE LIVES OF STARS (1), Introduction

           Stephen Maran in his book Astronomy for Dummies has an interesting analogy for the life cycle of stars:

          The most important star categories correspond to successive stages in their life cycles: babies, adults, seniors, and the dying. (What! No teenagers? The Universe gave up on youth classifications after the terrible twos!) Of course, no astrophysicists worth their Ph.D.s would use such simple terms, so astronomers refer to these types of stars as young stellar objects (YSOs), main sequence stars, red giants, and those in the end states of stellar evolution, respectively. (You’ll be glad to know that no star ever dies completely; at most, it “evolves” into a new and final state such as a white dwarf or a black hole.”)

          Regular guys like the Sun live out normal lives. Maran briefly but efficiently summarizes the life cycle of normal stars like the Sun as follows:

1. The star is created when gas and dust in a cool nebula condenses, forming a young stellar object (YSO). 2. Shrinking, the star dispels its remaining birth cloud, and its hydrogen fire ignites. In other words, nuclear fusion is underway… 3. As the hydrogen burns steadily, the star joins the main sequence… 4. When the star uses up all the hydrogen in its core, the hydrogen in the shell (a larger region surrounding the core) ignites. 5. The energy released by the burning of the hydrogen shell makes the star brighter and expands it, making the surface larger, cooler and redder. So it becomes a so-called red giant star. 6. Stellar winds blowing off the star gradually expel its outer layers, which form a planetary nebula around the remaining stellar core. 7. The nebula expands and dissipates into space, leaving just the hot little core. 8. The core, now a white dwarf star, cools and fades forever.

LIVES OF STARS (2) YSOs (Young Stellar Objects)

          At least two or three YSOs are observable with the present telescopes that can be found in the Philippines (either those in PAGASA or owned by Filipino astronomers). They are T Tauri, R Coronae Australis, and the Hubble’s Variable Nebula.

          I have observed two of them in the urban setting with perfect timing and luck; I have yet to see T Tauri, however. You will need a clear, cloudless, very transparent, and very young hour to see these objects. Taurus arrives during these hours when the rainy season in the Philippines is at its strongest and when Filipino astronomers observe the least.

 

 

http://youngstellarobjects.net

          An artist's conception of an actively accreting protostar. A protostellar system consists of an embryonic stellar core which is growing in mass via the accretion of material from a surrounding accretion disk, which itself is created and maintained but the infall of material from the surrounding protostellar envelope. The accretion process generates powerful bipolar jets and winds which emanate from the poles of the embryonic stellar core and which eventually disrupt the protostellar envelope driving the evolution of the system to the post-protostellar or PMS phase. Picture from an article by Tom Greene in the American Scientist, 2001, Volume 89, 316.

http://cfa-www.harvard.edu/rg/star_and_planet_formation/young_stellar_objects.html

 

 

          According to Stephen Maran in his book Astronomy for Dummies, YSOs are “newborn stars that are still surrounded by, or are trailing, wisps of their birth clouds.” The Hubble’s Variable Nebula looks like a comet with a fan-tail and a bright core. Stephen James O’Meara in his book The Caldwell Objects relates the discovery of the true nature of the Hubble’s Variable Nebula:

          …in 1966 Frank Low and Bruce J. Smith announced that R. Monocerotis was a “cocoon” nebula –dusty envelope of gas (out of which planet might from) around a new born star. R Monocerotis was the first nebula of this kind to be discovered; astronomers had predicted their existence just a year earlier. The team’s evidence was the large amount of infrared radiation. That R. Monocerotis emitted relative to its output of visible light. The scientist hypothesized that the visible light ultimately came from a new born star at the center of the dusty cocoon 200 astronomical units across. The tenth magnitude “knot” we see in our telescopes as R. Monocerotis, they argued, is the cocoon of dust being illuminated from within.

          R Coronae Australis is another star of this type, but its dust trail is harder to see. I needed two very transparent mornings to see it. O’Meara tells us that the comet-like fan tail of this star varies in brightness that coincides with the magnitude changes of the star itself. R Coronae Australis is a variable star. Its magnitude lies between 9.7 to 13.5.

          These two YSOs are good observing projects since their shapes vary in time. A pretty high-tech observer equipped with CCD cameras can document the shifts in the shape of these nebulae over time.

LIVES OF STARS 3, RED GIANTS

          One of the biggest objects we can see in the night sky is a red giant, Betelgeuse. In our light-polluted urban skies, we cannot see anymore the Andromeda Galaxy with the naked eye. I myself saw it with the naked eye in Noveleta, Cavite during one observing session conducted by the Philippine Astronomical Society. It was in 2002, before the Society split into two groups… What is a red giant star? I found it better to just copy the definition from the on-line Wikipedia Encyclopedia:

          Red giants are stars of 1000 times the volume of the Sun which have exhausted the supply of hydrogen which have exhausted the supply of helium core has no source of energy of its own, it contracts and heats up, and its gravity compresses the hydrogen in the layer immediately above it, thus causing it to fuse faster. This in turn causes the star to become more luminous (from 1,000 to 10,000 times brighter) and expand; the degree of expansion outstrips the increase in luminosity, thus causing the effective temperature to decrease. In stars massive enough to ignite helium fusion, an analogous process occurs when central helium is exhausted and the star switches to fusing helium in a shell, although with the additional complication that in many cases hydrogen fusion will continue in a shell at lesser depth — this puts stars onto the asymptotic giant branch The decrease in surface temperature shifts the star's visible light output to the red — hence red giant. Stars of sectral types O through K are believed to become red giants (or supergiants in the case of O and B stars).

http://en.wikipedia.org/wiki/Red_giant

          According to Stephen Maran in his book Astronomy for Dummies, a red giant “is not burning hydrogen in its core. In fact it’s burning hydrogen in a spherical region just outside the core, called a hydrogen-burning shell.” It cannot burn hydrogen anymore in its core because “it has already burned up all its core hydrogen, turning it to helium by nuclear fusion”, Maran explains.

          Betelgeuse is a supergiant among red giants, a Yao Ming among NBA centers. Bob Berman makes an interesting comparison in his book Secrets of the Night Sky: “The immensity of Betelgeuse can be grasped by a simple scale model. If we picture this leviathan as a globe big enough to enclose a twenty-storey building – take a moment to imagine it – then on the same scale our planet, Earth, would be the period at the end of this sentence.”

          The red giant phase in the life of the star represents an advanced stage in the life of that star. The Sun itself will bloat to become a red giant about 5 billion years from now.

LIVES OF STARS 4, STELLAR MASS

          Whatever will happen to a star would depend much on how massive it is. Our Sun, because it is not too massive by the standards of the more massive stars, will live a long but uneventful life. We have seen the Wolf-Rayet stars which would live a violent, spendthrift, but short lives.

          Let us start with the least massive stars. Patrick Moore in his book Atlas of the Universe explains that if the initial mass of the star is “less than one-tenth that of the Sun, the core will never be hot enough for nuclear reactions to begin, and the star will glow feebly for a very long period before losing its energy.” There is some controversy regarding this type of stars; we will discuss this later.

          If the initial mass is between 0.1 and 1.4 times that of the Sun, Moore emphasizes that “the story is very different. The star goes on shrinking, and fluctuates irregularly; it also sends out a strong stellar wind, and eventually blows away its original cocoon of dust.” This stage is the T Tauri stage. Pertaining to the Sun, its T Tauri stage lasted for about 30 million years, according to Moore. What happens next? Moore tells us that “When the core temperature soars to 10 million degrees C, nuclear reactions are triggered off; the hydrogen-to-helium process begins (known, misleadingly, as ‘hydrogen burning’), and the star will join the Main Sequence.”

          For how long will the hydrogen-to-helium process last? Moore relates what will happen:

          Hydrogen burning will last for around 10,000 million years, but at last the supply of hydrogen “fuel” must run low, and the star is forced to change its structure. The core temperature becomes so high that helium starts to “burn”, producing carbon; around this active core there is a shell where hydrogen is still producing energy. The star becomes unstable, and the outer layers swell out, cooling as they do so. The star becomes a red giant.

          What about those stars with a greater initial mass? They are thought to be candidates for supernova explosion, as far as the current theories are concerned. Moore explains:

          With stars of greater initial mass, everything happens at an accelerated rate. The core temperatures become so high that new reactions occur, producing heavier elements. Finally the core is made up principally of iron, which cannot “burn” in the same way. There is a sudden collapse, followed by an explosion during which the stars blow most of its material away in what is called a supernova outburst, leaving only a very small, super-dense core made up of neutrons – so dense that a thousand million tonnes of it could be crammed into an eggcup. If the mass is greater still, the star cannot even explode as a supernova; it will go on shrinking until it is pulling sp powerfully that not even light can escape from it. It has produced a black hole.

LIVES OF STARS 5, MAIN SEQUENCE STARS

          Our Sun is in the main sequence part of its life. It has been shining for about 4.5 billion years and will continue to shine as it is in its present stage for another 5 billion years. The Sun is a regular guy, spending its energy thriftily. According to Stephen Maran in his book Astronomy for Dummies, “When astronomers and newspaper science writers refer to ‘normal stars,’ they often mean main sequence stars. When they write about ‘sunlike stars,’ they mean main sequence stars with roughly the same mass as the Sun, give or take a factor of no more than two.”

          The longevity of main sequence stars is explained by its stable life. According to http://cse.cosm.sc.edu/hses/StarEvol/pages/main.htm

          The mass of a star governs where it plots in the main sequence. Once a star becomes a main sequence star, it becomes stable. This stability results because gravitational contraction of the core is balanced by the outward flow of energy of fusion. The loss of heat from the star’s surface is replenished by the emission of heat during fusion in the core. Therefore, in a main sequence star, fusion takes on the task of maintaining the star’s supply of radiation and keeping it from collapsing. As long as the forces of gravity and the outward flow of fusion energy are balanced, the star maintains its size.

          Look at your H-R Diagram. Almost 90% of the stars fall in the diagonal ribbon that stretched from the bottom right to the upper left of the Diagram. Our Internet source informs us about which stars in the main sequence will have a longer life:

          But, which lasts longer, a more massive main sequence star or a less massive main sequence star? It might seem reasonable to assume that a larger star, with more “fuel” in its core, would last longer. However, the larger stars are also hotter as shown on the H-R diagram. This higher temperature causes the rate of fuel consumption, or fusion, to be higher in larger stars. As a result, smaller main sequence stars remain stable longer than larger stars. It is estimated that main sequence stars more massive than 30 Sun masses last as short a time period as 100,000 years. Main sequence stars with a mass approximately equal to 0.2 Sun masses could conceivably last more than 200 billion years.

          We may wonder about the fate of our Sun. I have read somewhere that a species usually lasts for about 2 million years before it disappears. It may become extinct, perhaps, or it may evolve into another species similar to but quite distinct from the original species. The human species has already existed for 2 million years, so we should we on the verge of extinction or evolution. Either we will do it by destroying ourselves, or by modifying ourselves by means of technology, or perhaps some cataclysmic event will happen of which we do not have control. In the day after, how long will the Earth be able to sustain life? According to our source,

          Our Sun is thought to have a main sequence life span of approximately 10 billion years. So, how long will our Sun continue to emit the heat and light necessary to sustain life on Earth? While it is not known exactly how old our Sun is, we do know that the oldest known rocks on Earth are known to be at least 4 billion years old, based on radioactive dating. If we assume that the Earth formed at about the same time as the Sun (approximately 4.5 billion years ago), our best estimates are that the Sun will continue to support life on Earth for another 5 billion years.

WHITE DWARFS

          White dwarfs are stars in the end of stellar evolution, those which Stephen Maran in his book Astronomy for Dummies refers to as a “polite, catchall term for stars whose best years are far behind them.”

           Maran emphasizes that white dwarfs “can actually be blue, white, yellow, or even red, depending on how hot they are.” White dwarfs are the remains of sunlike stars which just fade away and never die like old generals according to General Douglas MacArthur.

          How does a white dwarf form? From http://memory-alpha.org, we can read the following short explanation:

          A white dwarf is a star formed when a red giant runs out of helium fuel after losing most of its mass into space. This leaves only the core, which is not producing any heat via nuclear fusion. As a result there is nothing to stop gravity collapsing the core down to a very small size (~10km). At this point the electrons in the core are so closely packed that quantum effects provide a counter force and the core stabilizes.

          The resulting white dwarf is extremely hot and dense, although not as dense as neutron stars or black holes. Because they contain only residual heat from the stellar lifetime, white dwarves eventually cool to become black dwarves.

          The picture below is taken by the Hubble Space Telescope. From the website of the National Aeronautics and Space Administration, we learn that extremely old white dwarfs have been detected by the HST:

          Pushing the limits of its powerful vision, NASA's Hubble Space Telescope uncovered the oldest burned-out stars in our Milky Way Galaxy. These extremely old, dim "clockwork stars" provide a completely independent reading on the age of the universe.

          The ancient white dwarf stars, as seen by Hubble, are 12-13 billion years old. Because earlier Hubble observations show that the first stars formed less than 1 billion years after the universe's birth in the big bang, finding the oldest stars puts astronomers well within arm's reach of calculating the absolute age of the universe.

http://www.nasa.gov/multimedia/imagegallery/image_feature_734.html

          Maran points out that “So much matter is packed into such a small space in a white dwarf star that a teaspoon of it would weigh about a ton on Earth.”

          The best example of a white dwarf that is possible to actually see is Sirius B, the companion of Sirius. I have seen this star using various telescopes; I have even seen it with the Astroscan at only 35x! James Kevin Ty, the President of the Astronomical League of the Philippines, told me that I had to use a magnification of no less than 200x just to detect it. Allen Yu, long time astronomer, thought it was an artifact of the telescope when he saw it with James’ venerable Televue 101, but was convinced later that he was seeing the real thing. The Oxford Dictionary of Astronomy says that Sirius B “can be seen only with large telescopes when at its maximum separation from Sirius.” Sometimes you just have to ignore the rules and just observe…

SUPERNOVAS or bomba stars

          When the astronomy bug bites you and you are hooked to astronomy, you will soon observe the Messier Objects. The very first object in this list is M1, a supernova remnant in Taurus. When I brought the Astroscan in Assumption College in Antipolo a few years back, M1 was clear and bright, but tiny at 35x in that small but very efficient telescope. There was no effort at all in seeing it. In my Celestron 8-inch Schmidt-Cassegrain, I had a terrible time finding it in the RTU Pasig Campus because of light pollution but I was able to see it.

           Stephen Maran in his book Astronomy for Dummies simply defines supernova as “enormous explosions that destroy entire stars.” There are several supernova types, but we will concern ourselves with just two for the meanwhile.

          Type II supernovas are described beautifully by Patrick Moore in his book Atlas of the Universe:

          A Type II supernova…is the result of the sudden collapse of a very massive supergiant – at least eight times as massive as the Sun – which has used up its nuclear fuel, and has produced a nickel-iron core which will not “burn.” The structure of the star has been compared with that of an onion. Outside the iron-rich core is a zone of silicon and sulphur; next comes a layer of neon and magnesium; then layer of carbon, neon and oxygen; then a layer of helium, and finally an outer-region of hydrogen. When all energy production stops, the outer layers crash down on to the core, which collapses; the protons and electrons are forced together to make up neutrons, and a flood of neutrinos is released, traveling right through the star and escaping into space. The temperature is now 100, 000 million degrees C, and there is a rebound so violent that most of the star’s material is blown away, leaving the neutron-star so dense that at least 3, 500 million tones of its materials could be packed inside a matchbox. The peak luminosity may be around 5, 000 million times that of the Sun.

          Life on Earth, and ourselves, would not have been possible if there have been no supernovas. Ken Croswell in his article Flourine, An Elementary Mystery (Sky and Telescope, September, 2003) explains that

          Every chemical element on Earth tells a story written in heavens. The nitrogen in our atmosphere and in your body’s proteins blossomed in stars somewhat heavier than the Sun, like Capella, which cast their outer layers away as planetary nebulae when they died. The oxygen you breathe and the neon gas in storefront lights were cooked up in massive stars like Antares, which later spewed these elements into galaxy by exploding as supernovae. And supernova explosions themselves forged much of the iron in your blood and the gold in your jewel.

          “Our progenitor was a supernova,” as Bob Berman explains to us in his book Secrets of the Night Sky. “We are made of stardust,” he adds. Dust for supernova explosions hurtle through space. For millions of years they saturate the primordial nebula from which our Solar System originated.

          There is another supernova type that deserves our attention. It is the Type Ia supernova. Maran explains to us this type:   

          Type Ia supernovas all produce similar explosions because they are eruptions in binary systems in which gas from one star flows down onto the other (a whit dwarf), building up an outer hot layer that reaches a kind of critical mass and then explodes, shattering the star. With less than critical mass, no explosion occurs; with critical mass, a standard explosion results…

          What about if the critical mass is exceeded? Maran quickly adds that “you can’t have more than critical mass because the star will have exploded!

DOUBLE AND MULTIPLE STARS

          Double and multiple stars are pleasant objects to observe, and sometimes they get challenging, too. They have the power to surprise audiences in star gazing activities, especially when they look at a binary for the first time. One famous double star is Alcor-Mizar in Ursa Major. It can be found in the asterism The Big Dipper. With the naked eyes, you can see one bright star with a dim companion that is barely visible. Through a telescope, the bright star is split into two components! Some stars are really two or several stars when you examine them in a telescope.

          Double stars are born together from one nebular cloud. The Great Orion Nebula is right now giving birth to thousands of stars. The Solar System was formed from a nebula, and it is possible that it was one star among a star cluster that has since dispersed, like children in a family that stay together while young and go their separate ways as they seek their own destinies. The Sun is one of the single stars, or is it? There are speculations that the Sun could be presenting itself as single when in fact it has a companion! According to Giles Sparrow, “A casual glance at the night sky shows that it seems to be full of single stars, similar to our Sun. But in fact most of our galaxy’s stars belong to double- and multiple-star systems, containing two, three, or even more stars orbiting each other.”

          How do double and multiple stars form? According to Sparrow,

          Multiple stars begin their lives in the same way as single stars, within collapsing clouds of gas and dust. Instabilities cause the cloud to separate into smaller chunks in orbit around each other, and the stars continue to collapse until they join the main sequence and begin to shine. Although systems of three or more stars are not uncommon, double or binary systems seem to form most easily. They account for more than half the stars in our galaxy, and many larger systems are built up from close, double-star pairs.

          Some double stars are either optical doubles or physical doubles. Optical doubles are not gravitationally bound while physical doubles orbit around their common center of gravity. Some doubles can be seen by the naked eye, or through the telescope. Others can be detected only by means of other methods.

          Stuart Clark in his book Encyclopedia of Stars and Atoms explains the astrometric method of looking for binary stars:

          Many double stars cannot be seen as visual binaries. Perhaps the star system is too far away for the separate components to be resolved, or perhaps it is relatively near but the two components are too close together. Sometimes one component is much fainter than the other and is outshone as a result. The components of a binary star system orbit each other around their common center of mass – neither star is stationary. If this oscillating motion can be detected in relation to the background stars, it indicates that a small or dim companion star is in orbit around the larger, brighter one. Such pairs are known as astrometric binaries.

          Clark explains another method of finding binaries by means of their spectra:

          Another method of finding binaries is to study their spectra. The spectral absorption lines may indicate the presence of two stars, each with a different spectral classification. Even if the stars are exactly the same type, they are in motion and this causes the spectral lines to alter in wavelength. This is because the wavelength of radiation emitted form a moving object is either stretched or squashed, depending upon whether the object is approaching or receding – this phenomenon is known as the Doppler effect. The stars are moving in different directions, causing the spectral lines to alter their wavelengths by different amounts. As a result, in the course of a single orbit the spectral lines move apart and come back together twice. If the companion star is too faint, its spectrum is swamped by that of the brighter star. That spectrum still exhibits the Doppler shift, however, and the presence of a companion can be inferred from that. This system is called a spectroscopic binary.

          The study of binary star systems is very important to astronomers for the value it gives to science. Clark explains this part:

          Binary star systems provide an opportunity for astronomers to weigh stars. To do this, the distance between the stars and the time it takes for them to complete an orbit must be measured. Using simple mathematics, a figure for the combined mass of the two stars can then be calculated. An estimate as to which star contains the most mass must then be made. If the two stars are identical, however, the figure can simply be halved. 

          Stephen Maran in his book Astronomy for Dummies gives us some additional information on this:

          The two stars in a binary system have orbits that are the same size if they have equal mass, and unequal size if they have unequal mass. The general rule is, the big guys follow smaller orbits…In binary systems, the big star that follows the smaller orbit travels more slowly than the little star in the big orbit. In fact, their respective speeds depend on their respective masses. The star that has one-third the mass of its companion moves three times as fast. By measuring these orbital velocities, astronomers can determine the relative masses of the members of a binary star.

          And then there are triple star systems. I think the best example of this is Beta Monocerotis, a true ternary system. The members are of yellow-orange color. Maran compares a three-star system to “wedded (or unwedded) bliss”:

          …a triple star system, like a binary system, consists of three stars that are held together by their mutual gravitation and that all orbit a common center of gravity… “Three’s a crowd” is a common expression of the instability in most romantic arrangements when a third person becomes involved. The same is true of triple star systems: They actually consist of a close pair or binary system and a third star in a much bigger orbit. If all three stars were on close orbits, they would interact gravitationally in chaotic ways, and, before you knew it, the group would break up as at least one star flew away, never to return.

          I thought Beta Monocerotis looked like three giggling wedding sponsors or “abays” who shared secrets among themselves…

          There are also quadruple star systems consisting of two close binary star systems that each revolve around the common center of mass of the four stars. The best example of this double-double system is Mizar in Ursa Major or Zeta-1 and Zeta-2 Ursae Majoris. In the telescope they are a double star but both components are themselves spectroscopic binaries. Castor, or Alpha Geminorum, is a six-star system! Epsilon Lyrae is another fine double-double with all components that can be observed in a good telescope.

          Multiple star systems contain components which are more than four in number. What is the difference between an open cluster and a multiple star system? Can we consider Theta Orionis, more famously known as the Trapezium, as an open cluster?

 

Here are some very nice double and multiple star systems from Patrick Moore’s Atlas of the Universe. Observe as many as you can:

SELECTED DOUBLE STARS

 

Name	Mag.	Sep.,”	P.A.,°	Map	Notes
γ Andromedae	2.3,5.0	9.4	064	12	Yellow, blue B is double
ζ Aquarii	4.3,4.5	2.0	196	14	widening
γ Arietis	4.8,4.8	7.6	000	12	Very Easy
α Canum Venaticorum	2.9,5.5	19.6	228	1	Yellow, bluish
α Centauri	0.0,1.2	17.3	218	20	V. easy. Period 80 years.
γ Centauri	2.9,2.9	1.2	351	20	Period 84 years
δ Cephei	Var ,7.5	41	192	3	Very easy
α Crucis	1.4,1.9	4.2	114	20	Third star in field
β Cygni	3.1,5.1	34.1	054	18	Yellow, blue
γ Delphini	4.5,5.5	9.3	267	18	Yellow, bluish
υ Draconis	4.9,4.9	62	312	2	Naked-eye pair
θ Eridani	3.4,4.5	8.3	090	22	Both white.
α Geminorum	1.9,2.9	3.5	072	17	Widening
α Herculis	Var ,5.4	4.6	106	9	Red, greenish
ζ Herculis	2.9,5.5	1.4	261	9	Period 34 years.
ε Lyrae	4.7,5.1	207	173	18	Both double
ζ Lyrae	4.3,5.9	44	149	18	Fixed, easy.
β Orionis	0.1,6.8	9.5	202	16	Not difficult
ζ Orionis	1.9,4.0	2.4	162	16	Split with 7.5 cm
β Phoenicis	4.0,4.2	1.5	3.24	21	Widening
α Scorpii	1.2,5.4	2.7	274	11	Red greenish
υ Scorpii	4.3,6.4	42	336	11	Both double
θ Serpentis	4.5,4.5	22	104	10	Very easy
β Tucanae	4.4,4.8	27	170	21	Both double
ζ UrsaeMajoris	2.3,4.0	14.4	151	1	Naked-eye pair with Alcor.
γ Virginis	3.5,3.5	2.2	277	6	Period 171 years. Closing.

BROWN DWARFS, Mga Bituing Walang Ningning

          When the International Astronomical Union was deliberating last July, 2006 on whether Pluto would retain its status as a planet, I e-mailed Dr. Cynthia Celebre about how brown dwarfs would tend to confuse whatever definition of “planet” the IAU might formulate. Brown dwarfs are intermediate in size and coolness between a regular planet as we understand them, but much dimmer and cooler than regular stars, or technically, those that fall under the spectral classes of WOBAFGKMNS.

          According to Gibor Basri in his article A Decade of Brown Dwarfs(Sky and Telescope, May, 2005), brown dwarfs were thought to comprise an astronomical “missing link”. According to Basri, “Straddling the divide between stars and planets, brown dwarfs may form like the former but look like the latter.” How do brown dwarfs form, according to prevailing theory in their formation? Basri explains:

          Theories for how these brown dwarfs should appear were first proposed in the 1960s, and they made it clear that the problem was likely observational. After all, theorists realized, any object with less than about 75 Jupiter masses would not steadily fuse hydrogen into helium for billions of years. Instead, such objects first would light up by dissipating gravitational energy while contracting (as young stars also do). Then they would fuse hydrogen – at least in the form of its heavy isotope, deuterium – for just a few million years. After that they would be supported by a special sort of internal pressure (electron degeneracy) that doesn’t require heat, and they would slowly fade while contracting at a glacial pace. (Gas balls with less than 13 Jupiter masses can’t muster hydrogen fusion at all and are generally considered planets.)

          Basri reports that brown dwarfs usually come in pairs, or binary systems, but the separation of the components is much smaller than in regular binaries. Some brown dwarfs have also been found to orbit Sun-like stars. Should they be considered planets? Basri, however, elaborates that brown dwarfs form in much the same way as regular stars, but they could have started in very small interstellar could cores; the material needed to form a regular star was not sufficient. It is also possible that before the brown dwarfs were able to fully develop as stars, their development was interrupted, making them in effect “stillborn stars”. The interruption could have happened when brown dwarf candidates were ejected from a small stellar subcluster. According to Basri,

          “A gravitationally bound multibody system tends to have unstable orbits, and its members keep exchanging orbital energy with one another. The smallest objects will likely be ejected, tightening the mutual orbits of the survivors. If this were to happen early in the cluster’s formation, the ejected objects would lose contact with their placental gas supplies before accreting enough material to become stars.

          Basri admits that we have a lot of job to do to fully understand brown dwarfs, but the “field brims with promise.” Basri concludes that “brown dwarfs fill the niche between stars and planets in many ways. In addition to having intermediate masses, they also have atmospheric temperatures that span the range between stars and planets, and their chemistry, cloud formation, magnetism, and other properties do so as well.

VARIABLE STARS, Types

          Even a casual observer with binoculars would notice brightness changes in Algol, or Beta Persei if he looks hard and long enough in the direction of the constellation Perseus. While working on my study about deep-sky objects I have seen how Mira in Cetus disappear at times and you would not be able to find it without the use of a telescope. Following the ups and downs in the brightness of variable stars is a good observing project for astronomers, only if our weather in the Philippines would cooperate.

          According to Giles Sparrow in his book The Universe and How To See It, there are “over 50 different types of variable stars known.”

          Some change their brightness in a matter of hours, some over months, and some over years. Some vary by just a fraction of magnitude, whereas others change by many magnitudes. Furthermore, some have steady and predictable cycles, but others may lie dormant for years before suddenly brightening in a brilliant outburst.

          Algol, known in antiquity as the Demon Star, is an eclipsing binary. What are these eclipsing binaries?

          According to Sparrow, They are double systems in which one star periodically passes in front of and behind the other, so that the overall light reaching Earth from the system drops rapidly, then rises again. If two stars in the system are of equal luminosity and size, then the two dips in brightness are equal. But more often the two stars are different, so the fluctuation in light will vary. If the two stars are close enough together, then the gravity may distort one or both into an egg shape so that they orbit, the visible surface area and therefore brightness, is constantly changing.

          Mira, on the other hand, is a pulsating variable star. According to Stephen Maran in his book Astronomy for Dummies, “Pulsating stars bulge in and out, getting bigger and smaller, hotter and cooler, brighter and dimmer. These stars are in a physical condition where they simply oscillate like throbbing hearts in the sky.”

          Another important type of variable star is the erupting variable stars. Sparrow explains the nature of these stars:

          Erupting variables are stars that show violent activity in their upper layers. Our own Sun shows a pattern of increasingly violent surface activity over an 11-year cycle. However, the Suns over all light output barely changes. By contrast, surface activity on an erupting variable has a far greater effect on the star’s overall brightness. For example, flare stars are very dim, red dwarf stars that nevertheless produce enormous flares, which can easily double their light output: and T Tauri variables are Sun like stars going through a phase of rapid brightness changes before settling into onto the main sequence. Other stars maybe more brilliant than the Sun, but still generate flare bright enough to affect their magnitude.

          Another variable star type we should know is the Cepheid Variable. According to Stephen Maran in his book Astronomy for Dummies, Cepheid variables are “The most important pulsating stars, from a scientific standpoint.” This is because Cepheids have a period-luminosity relation. According to Maran, “the longer the period of variation (the interval between successive peaks in brightness), the greater the true average brightness of the star.” In knowing the true brightness of the star, astronomers can determine the distance to the star. The inverse square law states that when stars are twice as far away, it is four times as faint, or when it is three times farther away, then it is nine times as faint.

NEUTRON STARS

          Here is another sort of exotic star. Its properties tax the imagination. According to Stephen Maran in his book Astronomy for Dummies, “A teaspoon of neutron star would weigh about a billion tons on Earth” According to http://imagine.gsfc.nasa.gov, neutron stars are “fascinating objects because they are the most dense objects known. They are only about 10 miles in diameter, yet they are more massive than the Sun. One sugar cube of neutron star material weighs about 100 million tons, which is about as much as a mountain.” From the same source, we learn that neutron stars “can also have magnetic fields a million times stronger than the strongest magnetic fields produced on Earth.”

          So, how are these objects produced? Our internet source explains:

Neutron stars are compact objects that are created in the cores of massive stars during supernova explosions. The core of the star collapses, and crushes together every proton with a corresponding electron turning each electron-proton pair into a neutron. The neutrons, however, can often stop the collapse and remain as a neutron star.

          The Oxford Dictionary of Astronomy further illustrates the density of a neutron star. It says that “the mass of the entire human race would occupy the volume of a sugar cube.”

OPEN CLUSTERS By Jesus Rodrigo F. Torres

          Open clusters are some of the most fascinating objects to observe. I often let my imagination take flight whenever I see an open cluster. I often imagine myself riding on a planet orbiting a star in an open cluster. What would the night sky in that planet look like? Another aspect of open clusters which make them so enjoyable to observe is the patterns that could be made if we play connect-the-dots with its individual stars. Many open clusters get their appellations from astronomers this way. M6, for example, in Scorpius, looks like a butterfly, so astronomers call it the Butterfly Cluster. NGC 457 in Cassiopeia seems to look like an E.T. with red bulging eyes, so they call it The E.T. Cluster.

          What is an open cluster? According to the Oxford Dictionary of Astronomy , an open cluster is “A group of stars formed together in the spiral arms of a galaxy.” The same source tells us that they are sometimes called galactic clusters, and that they “are usually irregular is shape and contain anything from a few dozen to several hundred relatively young stars in volume up to 50 light years across.”

          The stars in open clusters condense from some primordial nebula, and some of them still retain traces of the nebula from which they formed. Open clusters contain a variety of stars, and if you are lucky, you will see through a telescope some open clusters with stars of various colors which make them look like scattered jewels on black velvet. The Jewel Box in the constellation Crux, also known as NGC 4755 or the Kappa Crucis Cluster. According to the Oxford Dictionary of Astronomy , M6 or the Butterfly Cluster is also called the Jewel Box. The Jewel Box in Crux contains many bright blue and white stars while a bright orange one steals the scene like some beauty queen dramatically entering into the grand ballroom.

          According to Giles Sparrow in his book The Universe and How to See It, “Clusters form with a wide range of stars of different masses from blue giants to red dwarfs” which explain why some open clusters have a multi-colored collection of stars. Sparrow also explains why open clusters are important in our understanding of the lives of stars. Here’s how:

          Clusters form with a wide range of stars of different masses from blue giants to red dwarfs. Since all these stars were born within a few million years of each other, they can be reckoned to be the same age in cosmic terms, so astronomers can observe how some live their lives faster than others. The heaviest stars form most quickly, and join the main sequence while smaller stars are still condensing. As these massive, hot, blue stars begin to shine, their radiation blows away much of the nearby nebula, denying smaller nearby stars the chance to grow and often creating an emission nebula. As the nebula ages, smaller and lighter stars join the main sequence. But by the time the smallest dwarfs begin their lives, the massive blue giants are already moving off the main sequence, swelling into red giants as they exhaust their primary sources of fuel.

          Stan Gibilisco in his book Astronomy Demystified asks a question: “How do we know that the stars in an open cluster are associated and are not just accidentally close to each other because they happen to fall along the same line of sight relative to Earth?” Gibilisco gives us his own answer:

          One way to find out is to measure the radial speeds of the individual stars relative to us and then compare these speeds. If the stars are in a common group, held in each other’s vicinity by gravity, then we should not observe much difference in the radial speeds of the stars. If, however, we’re just seeing coincidental lineup of stars, the individuals in the swarm should have much different radial speeds, just like stars chosen at random in the sky. It turns out that the stars in an open cluster all have radial speeds that are nearly identical.

          How do we know the distance of open clusters from the Solar System? Sparrow informs us that their distances can be determined from how the stars in a cluster move: “The movements of stars within a cluster also allow astronomers to work out its distance using a form of parallax effect. If the cluster is nearby, then its member will appear to be moving apart in the sky far more rapidly than the members of a more distant cluster”
          
          Sparrow also informs us about how the age of the cluster can be determined from the study of the concentration of the stars in the cluster, in addition to their spectral types. Sparrow explains that “Most clusters are relatively young -- just a few hundred million years old – because the older a cluster gets, the more dispersed it becomes. Each star has its own motion, and they gradually scatter across space.” Just like brothers and sisters who live together only while they are young…

Here are some clusters that you must have to observe:

The Pleiades in Taurus

The Hyades, also in Taurus

The Double Cluster in Perseus

The Beehive in Cancer

NGC 6231 in Scorpius

The Jewel Box in Crux

M6 and M7 in Scorpius

GLOBULAR CLUSTERS By Jesus Rodrigo F. Torres

          Whenever I study a globular cluster through a telescope I always think how inhabitants in a planet there would see their night sky. Will they see galaxies? Will they enjoy a real night with real darkness? Or will there be no night at all in their planet? Sometimes I wonder if heaven is in a globular cluster. The Holy City in Revelation is a place which “did not need the sun or moon for light…and there will be no night there…” (Revelation, 21:23-26). I asked Prof. Arthur Arriola if astronomers would be welcome in the Holy City, and he told me that maybe astronomers would have the freedom to roam the Universe at will without need of space ships!

          According to the Oxford Dictionary of Astronomy , a globular cluster is “a roughly spherical group of old stars in the halo of a galaxy.” The dictionary informs us that “about 140 globular clusters are known in our Galaxy, traveling on highly elongated orbits around the galactic center.” Just how old are the stars in globular clusters? “They are very old,” according to the dictionary, “about 10 10 years, having formed early in the history of the Galaxy.” Stephen James O’Meara in his book The Caldwell Objects describes globular clusters in this manner:

          Globular Clusters are the Milky Way’s senior citizens. When our galaxy was an adolescent, some 10 to 16 billion years ago, thousands of globular clusters are thought to have formed from its original allotment of gas. The clusters may even have begun life as the cores of dwarf galaxies. In time though, most of this primordial perished in repeated, tragic encounters with each other or with the galactic center. Today, only about 150 globulars – the remnants of the largest dwarf galaxy? - are known to have survived these ravaging encounters .

          These globular clusters are found in the halo of our galaxy, “seemingly surrounding our Galaxy on all sides,” according to Robert Burnham in his classic work the Celestial Handbook . Burnham continues:

          When the distribution of these objects is plotted, it is found that they form a nearly spherical system and that the center of this system is identical with the center of our Galaxy. This discovery was made by Harlow Shapley. It has since been found that other galaxies are accompanied by their own globular cluster families; the Andromeda spiral for example has about 140, and the great elliptical galaxy M87 in Virgo possesses well over a thousand.

          How many stars are there in globular clusters? The Dictionary tells us that they “contain from tens of thousands to millions of stars, and have diameters of 100 to 300 light years.” Burnham describes how the sky in a hypothetical planet in M13 or the Hercules Cluster (magnificent globular cluster in the constellation Hercules) would look like:

          The appearance of the heavens from a point within the Hercules Cluster would be a spectacle of incomparable splendor; the heavens would be filled with uncountable numbers of blazing stars which would dwarf our own Sirius and Canopus [the brightest stars in apparent magnitude] to insignificance. Many thousands of stars ranging in brilliance between Venus and the full moon would be continually visible, so that there would be no real night at all on a planet in a globular cluster. Inhabitants of such a planet would probably know nothing of other clusters, of the Galaxy, and of other galaxies, as their view would be completely blocked by the brilliance of their own skies. To them, the Hercules Cluster would be “the Universe”.

          When you have the opportunity to view a globular cluster through a telescope, imagine how concentrated the stars seem to be. Are stellar collisions in globular clusters common? Burnham illustrates to us how they can be just mostly empty space, if we can only come inside a globular cluster itself:

          Photographs give the impression of incredibly thick crowding and suggest that the stars are packed virtually in contact. This is an illusion, due to the vast distance of the group and the merging of the numberless star images. The central region covers an area some 100 light years in volume. Assuming that a million stars populate this region it is evident that the density is no greater than about one star per cubic light year. In the actual center of the cluster the star density may be several times greater, but in no case would it approach actual crowding. This fact is better understood by constructing an imaginary scale model of the cluster. On such a model the stars would be represented by a million grains of sand, distributed throughout a spherical volume of space some 300 miles in diameter. Each grain would be 0.03 inch in diameter, and separated from the next nearest grain by a distance of three miles! Even in the most closely packed central mass the grains would still be separated from each other by the greater part of a mile. Thus, even the globular cluster, which appears to us as the most densely packed mass of stars to be found anywhere in the Universe, is shown to be, by earthy standards, almost empty space.   

          But stellar collisions and mergers do happen in globular cluster. O’Meara explains to us a phenomenon observed in 47 Tucanae, a magnificent globular cluster which I have not observed myself due to its very southerly location. In this globular cluster, blue stars were discovered, and we know that blue stars are relatively young stars. They have been called the Blue Stragglers ever since. O’Meara explains their presence in 47 Tucanae:

          Globular clusters harbor some of the oldest stars known in our galaxy. But when the Hubble Space Telescope peered into the heart of 47 Tucanae, it revealed that the cluster’s entire core is crowded with mysterious “blue stragglers” – stars that are bluer and brighter than the other cluster members, as if somehow they were born more recently than their siblings. Blue stragglers were discovered about half a century ago and were enigmatic until recently. However, in recent years astronomers have become convinced that these stellar non-conformists are formed either when the stars in a double-star system slowly merge or when two unrelated stars collide. Data from HST’s Faint Object Spectrograph established the temperature, size, and rotation rate of one massive blue straggler (BSS-19) in 47 Tucanae. And for BSS-19, at least, astronomers favor the slow merger scenario. BSS-19 has a mass of 1.7 Suns; it is the first globular-cluster blue straggler whose mass has been measured directly.

          Here are some globular clusters we have to see:

M13 in Hercules

M5 in Serpens

Omega Centauri

M22 in Sagittarius

NGC 1851 in Columba

M79 in Lepus

M3 in Canes Venatici

M15 in Pegasus

NGC 1851  

          A globular cluster in the constellation of Columba, below Lepus and Canis Major, This cluster shines at magnitude 7.2, has a dense, bright unresolvable core, surrounded by fainter and looser concentric rings of stars.

http://www.paulandliz.org/Star_Clusters/Globulars.htm

 NGC 2419

          At magnitude 10.3, located in Lynx, near Auriga, this little cluster is known as the "Intergalactic Wanderer" because it is 300,000 light years from our Galaxy's center and has a true space velocity which is greater than that needed to escape from our Galaxy at its location.  There are no other globulars near it, and astronomers assume that the Milky Way has lost its grip on this little fellow.

http://www.paulandliz.org/Star_Clusters/Globulars.htm

PLANETARY NEBULAE

By Jesus Rodrigo F. Torres

          Planetary nebulae are beautiful objects to behold. They come in many shapes and sizes. I have seen one of them shaped like a ring. Some have protruding appendages which make them appear like seeds just beginning to sprout. One looks like a foot, at least according to Dr. Luis Castaneda who joined me in many early observations. Most of them look pale blue to me but many other observers would swear they look green. Some have bright and big central stars with layers of smoky material surrounding the central star. There is a zoo of planetary nebulae in the night sky.

          According to the Oxford Dictionary of Astronomy , “planetary nebulae were so named because they appeared to early observers to resemble a planetary disk”. All the essential things we should learn about planetary nebulae are given in the Dictionary. It explains that “A planetary nebula forms when a red giant ejects its outer layers at speeds of about 10 km/s. The ejected gas is then ionized by ultraviolet light from the hot core of the star.”

          Just how fast is the ejection of the red giant’s outer layers? Is it abrupt? If it is abrupt, how can we explain the great variety of shapes planetary nebulae take? O’Meara explains this matter:

          Planetary nebulae once were believed to be the abruptly ejected atmospheres of massive red-giant stars. However, this simple theory could not account for the wild shapes seen in these objects. There is a veritable zoo of heavenly creatures among the planetaries, including silkworms, butterflies, and eggs wrapped in kudzu. In the late 1970s, Sun Kwok (now at the University of Calgary, Canada) and his colleagues conceived of a new theory of planetary-nebula formation. They started with a red-giant star sloughing off its outer atmosphere and exposing a white-hot core (a white dwarf in the making). They then envisioned superfast winds streaming out from the hot central star and compressing and accelerating the slower circumstellar material that was ejected earlier; the interacting winds would create the shell shapes we see in planetaries today. Kwok’s theory was vindicated when the International Ultraviolet Explorer satellite found that many planetaries’ central stars in fact have fast winds.

          It has been observed, however, that most planetary nebulae are bipolar. It means, according to Stephen Maran in his book Astronomy for Dummies , they “they consist of two round lobes projecting from opposite sides of the central star.”

          The central star of a planetary nebula is very hot. According to Robert Burnham in his Celestial Handbook ,

          In a study of 65 central stars of planetary nebulae G.O. Abell (1965) found photographic absolute magnitudes of 0 to about +10, with mean value near +5; temperatures range from 30,000 deg K up to about 400,000 deg K, and the computed diameter of the stars varied from less than 0.01 the solar diameter up to nearly the size of the Sun. These results support the conclusion of C.R.O’Dell (1964) that some of the central stars have the dimensions of true white dwarfs, and that the planetary nebula phenomenon probably represents a stage in the evolution of certain stars to white dwarf state.
          
          As I said above, planetaries appear mostly blue to me, but astronomers seem to be divided between those who can see them as green or blue. According to Michael Rowan-Robinson in his book,

          The intense ultraviolet radiation from the very hot central star strips electrons off the atoms of the gaseous shell, leaving them ionized. Free electrons captured by such atoms may have far more energy than the outer electrons in an atom usually have. The electrons dispose of this excess energy by emitting the difference in energy as light of a particular wavelength, the phenomenon of fluorescence. These wavelengths show up as bright lines across the spectrum of the nebula when its light is passed through a prism spectrometer. The typical bluish-green colour of planetary nebulae, for example, is due to two bright emission lines of doubly-ionized oxygen (two electrons stripped off each atom) in the green part of the spectrum.

          In a few thousand years, a typical planetary nebula would vanish. According to Burnham, “It is interesting to reflect upon the planetary nebulae we see today, speculating that they must be ephemeral objects by astronomical standards, and are fated to expand outwards into invisibility in a mere 30 or 40 thousand years.”

          Rowan-Robinson explains that “The shells of planetary nebulae are found to be rich in carbon, nitrogen and oxygen [which are] by-products of the helium burning process…To reach the stage of helium ignition, a star must be at least as massive as the sun. Planetary nebulae are…the death throes of stars in the range 1-8 solar masses.”

          Given this information, of what importance are planetary nebulae to us? According to Rowan-Robinson,

          As carbon, nitrogen and oxygen are the key elements in the production of life, the beautiful shells of planetary nebulae are of more than just aesthetic interest. These