|12-30-2012, 03:19 PM||#1 (permalink)|
Join Date: Nov 2006
Location: Nashville, Tennessee
Deep sky objects fascinate both amateur and professional astronomers. Star-hoppers aim their telescopes at nebulas (interstellar clouds of hydrogen gas and dust) and planetary nebulas (which are dying stars, not nebulas at all). They target supernova remnants, star clusters (open & globular) and galaxies. Nomenclature is sometimes confusing as early astronomers had only vague ideas about what they were seeing.
..1 TRIFID NEBULA (M20) - The three-lobed Trifid Nebula combines an open cluster, an emission nebula, a reflection nebula and a dark nebula. An emission nebula glows on its own when excited by nearby stars. This is the pink part of the Trifid. A reflection nebula merely reflects the light of nearby stars. This is the blue part. It looks to me like the dark dust lanes split the Trifid into four parts instead of three. The Trifid is a stellar nursery in Sagittarius above the spout of the teapot.
..2 ORION NEBULA (M42) - Stars are forming in M42, one of the most popular targets in astronomy. It has taught us much about how stars form from collapsing clouds of dust and gas. The Hubble Space Telescope has observed protoplanetary disks around young stars, suggesting that solar systems are common. Nebulas like M42 form from clouds of compressed hydrogen to eventually become open clusters like the Pleiades.
There is an open cluster within the Orion Nebula called the Trapezium. There is considerable ultraviolet radiation. M42 is seen as the middle object in the sword hanging from Orion's belt. Its nebulosity is plain through binoculars. The famous Horsehead Nebula is near the star Alnitak in the belt. I may be the only one who sees a turkey in the nebula's shape!
..3 NORTH AMERICA NEBULA (NGC 7000) - This is an emission nebula in Cygnus the Swan. Its shape is remarkable. We can picture the United States and Canada, Mexico and Central America as well as Florida and the Gulf of Mexico.
..4 PILLARS OF CREATION - These columns of interstellar dust and gas were imaged by Hubble in the Eagle Nebula in the constellation Serpens. The picture became famous. New stars are being "created." The pillars may actually be gone because of the enormous distance their light has to travel.
..5 HORSEHEAD NEBULA (Barnard 33) - The Horsehead is the dark nebula in Orion. It passes for a chess piece, a black knight.
..6 DUMBBELL NEBULA (M27) - Yes! It looks like an apple core! M27 was the first known "planetary nebula," and again I will stress that this is a terrible name because it has nothing to do with planets. What we see is an expanding gas cloud resulting from the death of a sun-like star. A white dwarf resides at the center of the cloud. The Dumbbell is located in Vulpecula the Fox.
..7 RING NEBULA (M57) - Probably the most photographed deep sky object, the infamous Ring Nebula is found in Lyra. Karen calls it "the eye." In reality, it is a "planetary nebula." A shell of gas is expanding into space at a tremendous speed although we cannot detect its movement because it is so far away. A star ended its life as a red giant, leaving behind a white dwarf. The Ring is 2300 light-years away. The central white dwarf is dim at magnitude 15, illuminating the gas cloud by ultraviolet radiation. Our sun will undergo a similar process.
..8 OWL NEBULA (M97) - The Owl is a "planetary nebula" just below the Big Dipper. Features in the expanding gas resemble the eyes of a wise owl. Use your imagination! The dying white dwarf at its center is magnitude 16.
..9 ETA CARINAE - This is a double star marked by balloon-shaped gas clouds. It is located in the southern constellation Carina, and we observed it at the Southern Skies Star Party in Bolivia. Eta Car A is massive. It is burning its fuel quickly and is expected to go supernova in a million years. Its brightness doubled in the late 1990s. It is classified as a variable and notorious for outbursts. Should Eta Carinae go hypernova, its shock waves may affect Earth. Earth's atmosphere, however, protects it from gamma rays.
10 CRAB NEBULA (M1) - The Crab Nebula has the distinction of being first on Charles Messier's list. It is a supernova remnant in Taurus. This exploding star was recorded by the Japanese in 1054. The Crab is expanding at the rate of 1500 kilometers per second. We would never know it by looking! A pulsar lies at its center. A pulsar is a neutron star that spins. The Crab Pulsar spins 30 times a second while emitting electromagnetic radiation in the form of radio waves, X-rays and gamma rays. The Earl of Rosse named this remnant because he thought his drawing looked like a crab.
11 VEIL NEBULA - A supernova remnant, it is estimated to have exploded 10,000 years ago. Rope-like filaments of gas are all that remain. The Veil is located in Cygnus and divided into east and west.
12 BEEHIVE CLUSTER (M44) - This open cluster in Cancer is sometimes called Praesepe, which is Latin for manger. It has a large population of stars and contains many red giants and white dwarfs. It also has main sequence stars, those still converting hydrogen into helium. Both the Beehive and the Hyades star clusters are thought to be about 700 million years old. I spotted the Beehive from my parents' back yard in the spring of 1962.
13 PLEIADES (M45) - This is an open cluster of stars. Some people see six. Others see seven. The Pleiades were known as the Seven Sisters to the ancient Greeks. It is extraordinary how astronomical phenomena were seen in anthropomorphic terms before the scientific revolution. The ancients started with an ideology into which they tried to fit facts. Scientists gather facts, then formulate theories based on them. The Pleiades is in Taurus the Bull. It is obvious and almost impossible to miss. It is close to Earth in cosmic terms, and its distance has been measured using several methods. The distance to M45 is somewhere in the range of 130 parsecs. 1000 stars make up the cluster, and young, hot blue stars dominate. The Pleiades will disperse as all open clusters do.
The seven Pleiads are Alcyone, Merope, Electra, Maia, Sterope, Taygeta and Celaeno. Alcyone is the brightest. It is more luminous than our sun but far, far away. The nebulosity around the Pleiades is now thought to be interstellar gas that M45 is simply drifting through. I would call this an unlikely coincidence. The cluster resembles a little dipper.
14 HYADES - Like the Pleiades, the Hyades is an open cluster in Taurus. It is the closest star cluster to Earth, and its stars form a V-shape. Aldebaran, the bull's eye, is unrelated, being much closer. The Hyades is 700 million years old and dominated by red giants. In sky lore, the Hyades were half-sisters to the Pleiades. Atlas fathered them all, the Pleiades with Pleione and the Hyades with Aethra. All stars form in clusters, most of which dissolve after about 50 million years.
15 OMEGA CENTAURI (NGC 5139) - The largest and best of all the globular clusters, Omega Centauri is in the constellation Centaurus. We looked at it during the SSSP on the shore of Lake Titicaca. Globular clusters differ from open clusters. Globulars are outside the galactic disk and contain millions of stars tightly bound by gravity. Open clusters are dozens or hundreds of stars loosely bound inside the disk. They drift apart. Globulars are distant, and that Omega Centauri can be seen with the naked eye attests to its size. Omega Centauri, although a cluster, was named as if it were a star. Omega is the 24th letter of the Greek alphabet.
16 M13 - This is the globular cluster in Hercules. Edmund Halley found it, and Charles Messier cataloged it. I recall trying to locate it to no avail even though it is visible at 5.8 magnitude. There are hundreds of thousands of stars in M13, and something called the Arecibo Message was aimed at it in 1974. The problem is that by the time the message arrives, M13 will have moved on. The message was composed by Frank Drake of SETI fame.
17 LARGE MAGELLANIC CLOUD - The LMC is a galaxy and a satellite of the Milky Way. I saw both Magellanic Clouds at the South Pacific Star Party in Australia. Both were fainter than I imagined. They were named after the Portuguese navigator Ferdinand Magellan, who spotted them on his around the world voyage 1519-22. Data from the Hubble ST suggests that these two irregular galaxies may not be orbiting the Milky Way after all. The Tarantula Nebula is in the LMC, and open clusters have been found. I recall reading about the supernova of 1987 in USA Today, the paper subscribed to by my dad. The LMC has a healthy star formation fueled by its abundant dust and gas. The Milky Way would be awesome from the LMC.
18 SMALL MAGELLANIC CLOUD - The SMC lies 200,000 light-years away in the constellation Toucan. It is thought to have been a barred spiral that was disturbed by the Milky Way. There is a large population of X-ray binaries. Of course, Australian aborigines and the natives of the South Sea islands knew of the Magellanic Clouds long before Magellan.
19 ANDROMEDA GALAXY (M31) - M31 is visible to the naked eye, and I found it in the constellation Andromeda in the fall of 1961. It is a tiny smudge two stars down and two objects up from the square of Pegasus, best seen with averted vision. The Andromeda Galaxy contains a trillion stars, so it is far more than just a smudge. It is the largest galaxy in the Local Group and 2.5 million light-years distant. Its spiral shape approaches perfection. If there is no life or advanced civilization in M31, there may be none anywhere beyond Earth. The Milky Way and the blueshifted Andromeda Galaxy are on a collision course. In five billion years they will merge to form an elliptical. Can you imagine being around for that event, walking out of your house to see M31 cover the sky? A supernova was observed in 1917, and Edwin Hubble determined M31 to be an external galaxy after identifying Cepheid variables. M31 has a metal-rich halo with spiral arms wound in clockwise fashion. It has satellite galaxies, the best of which are M32 and M110.
20 TRIANGULUM GALAXY (M33) - This face-on spiral is called the Pinwheel Galaxy. We look at it and think there must be an intelligence, or a Creator. Then, Hawking's "spontaneous creation" crosses our minds, the realization that something did indeed come from nothing, that the universe does not need "God." M33 is in the Local Group of galaxies three million light-years away, a bit farther than M31. M33 contains 40 billion stars compared to the Milky Way's 400 billion. There is no central bulge and no black hole in the nucleus. M33 may become part of the Milky Way/Andromeda collision.
21 WHIRLPOOL GALAXY (M51) - The Whirlpool is a face-on spiral in Canes Venatici. It is interacting with NGC 5195. The Whirlpool is well-known and was the first galaxy to be recognized as a spiral. Supernovas appeared in 2005 and 2011. The Whirlpool is undergoing a high rate of star formation, and a black hole is thought to be at its center. Its curving spiral arms are majestic! NGC 5195 is behind the Whirlpool.
22 BLACKEYE GALAXY (M64) - M64 was found by Messier in 1780 and named for its spectacular lane of dust and gas. It looks like a black eye. It is a spiral in Coma Berenices whose stars orbit clockwise while gas on the outer edge orbits counterclockwise. M64 is 17 million light-years away.
23 M87 - M87 is a monster elliptical galaxy! Ellipticals tend to be the largest galaxies, keeping their shape because their stars orbit in random fashion. M87 is almost featureless. It is a source of radio waves and X-rays and has a humongous black hole at its center. A black hole this big may be the result of smaller black holes coming together. 12,000 globular clusters orbit M87 compared to a mere 200 orbiting the Milky Way. That globulars exist outside the planes of galaxies may account for their preservation. They are above the chaos! M87 is located in Virgo and has the mass of 200 Milky Ways. Charles Messier found it in 1781.
24 SOMBRERO GALAXY (M104) - This spiral in Virgo gets its name because it resembles a sombrero. There is a central bulge and a prominent dust lane. At magnitude 9, the Sombrero is accessible to amateur astronomers. An 8-inch telescope will resolve the bulge, which is host to a supermassive black hole. Hawking thinks that black holes may have been created by the Big Bang.
Jim Colyer "Girl Album" http://www.jimcolyer.com