Deep sky objects fascinate both amateurs and professionals. Star-hoppers aim their telescopes at nebulas (clouds of hydrogen gas and dust) and planetary nebulas (dying stars). They target supernova remnants, star clusters (open and globular) & galaxies. Nomenclature can be confusing because early astronomers had only vague ideas about what they saw.
..1 TRIFID NEBULA (M20) - This 3-lobed nebula has an emission nebula, a reflection nebula & a dark nebula. Emission nebulas glow on their own when excited by nearby stars. This is the pink part. Reflection nebulas reflect light from stars. This is the blue part. Dark nebulas block the stars behind them. This stellar nursery in Sagittarius is above the teapot's spout.
..2 ORION NEBULA (M42) - Stars are forming in the Orion Nebula. Stars form from compressed clouds of gas and dust. Nebulas like M42 will become open clusters. Hubble imaged disks around young stars, suggesting that solar systems are common.
..3 PACMAN NEBULA (NGC 281) - It is called Pacman because the dust cloud looks like a mouth. E.E. Barnard discovered it.
..4 RUNNING MAN NEBULA (NGC 1977) - A member of the Texas Astronomical Society named this blue reflection nebula near M42.
..5 NORTH AMERICA NEBULA (NGC 7000) - An emission nebula in Deneb, its shape is unmistakable. We see the United States and Canada, Mexico and Central America, Florida and the Gulf of Mexico.
..6 HORSEHEAD NEBULA (Barnard 33) - The Horsehead is a dark nebula in near Alnitak in Orion's belt. It looks like a chess piece, a black knight.
..7 PILLARS OF CREATION - These columns of gas and dust in the Eagle Nebula of Serpens were imaged by the Hubble Space Telescope. The picture is famous! New stars are being born. The Pillars may be gone because of the great distance their light had to travel.
..8 DUMBBELL NEBULA (M27) - The Dumbbell was the first known "planetary nebula." This is a bad name because these objects have nothing to do with planets. What we see is expanding gas resulting from the death of a star. A white dwarf is at the center.
..9 RING NEBULA (M57) - The most famous deep sky object, the Ring Nebula in Lyra is a planetary nebula. Its gas ring is expanding at a tremendous speed even though we cannot detect movement because it is so far away. The star ended its life as a red giant, leaving behind a white dwarf. Ultraviolet radiation from the dwarf illuminates the ring. Our sun will undergo a similar fate.
10 OWL NEBULA (M97) - The Owl is a planetary nebula below the Big Dipper. Features in the expanding gas resemble the eyes of an owl. Use your imagination! The white dwarf at the center is magnitude 16.
11 BUTTERFLY NEBULA (NGC 6302) - This planetary nebula (dying star) in Scorpius really does look like a butterfly.
12 CAT'S EYE NEBULA (NGC 6543) - This planetary nebula in Draco has been studied in optical, infrared, ultraviolet & X-ray wavelengths. It consists of hydrogen and helium with traces of heavier elements.
13 ETA CARINAE - This double star with balloon-shaped gas clouds is in the southern constellation Carina. I observed it at the Southern Skies Star Party in Bolivia. Eta Car A burns fuel rapidly and is expected to go supernova in a million years. It is a variable and notorious for outbursts. Should Eta Carinae go hypernova, shock waves may reach Earth. Fortunately, Earth's atmosphere protects it from gamma rays.
14 CRAB NEBULA (M1) - The Crab in Taurus is a supernova remnant and the first object on Charles Messier's list. The Chinese recorded it in 1054. The Crab is expanding at the rate of 1500 kilometers per second, although you would never know it by looking! A pulsar lies at its center. A pulsar is a neutron star that spins, and the Crab Pulsar spins 30 times a second. It emits radio waves, X-rays & gamma rays. The Earl of Rosse named this SNR because his drawing looked like a crab.
15 VEIL NEBULA - A supernova remnant whose star exploded, leaving rope-like filaments of gas. The Veil is split into east and west.
16 SNR1572 - Tycho's star in 1572 left a supernova remnant. It is in Cassiopeia and one of 8 supernovas in historical records.
17 COMA STAR CLUSTER - This is in the constellation Coma Berenices and represents Queen Berenice's hair. She was real and ruled in Egypt. The cluster was once Leo's tail.
18 BEEHIVE CLUSTER (M44) - This open star cluster in Cancer contains red giants and white dwarfs. It has main sequence stars, those still fusing hydrogen. I located the Beehive from my parents' backyard. The Beehive and Hyades clusters are 700 million years old.
19 HYADES - The Hyades is an open star cluster in Taurus. It is the nearest cluster to Earth, and its stars form a V. Red giants dominate. All stars form in clusters, most of which dissolve after 50 million years. In sky lore, the Hyades and Pleiades were half-sisters. Aldebaran is not part of the Hyades.
20 PLEIADES (M45) - The Pleiades is an open cluster. In Greek mythology, they were 7 sisters. Astronomical phenomena were explained in anthropomorphic terms before the scientific revolution. The ancients started with ideology into which they tried to fit facts. Scientists start with facts, then formulate theories. The Pleiades is in Taurus, impossible to miss. Young, hot blue stars dominate. The Pleiades will drift apart like open clusters do. The 7 Pleiads are Alcyone, Merope, Electra, Maia, Sterope, Taygeta & Celaeno. The Dance of the Pleiades is a marvelous painting by Elihu Vedder.
21 THE DOUBLE CLUSTER IN PERSEUS (NGC 869 & NGC 884) - They are visible to the naked eye, although I have never seen them. Both can be seen using a low-power eyepiece. The clusters are 7000 light-years from Earth in the next spiral arm.
22 M10 - This is a globular cluster in Ophiuchus. It is magnitude 7 and 14,300 light-years distant. It was discovered by Charles Messier and resolved into stars by William Herschel.
23 M13 - This is the famous globular in Hercules. Edmund Halley found it, and Messier cataloged it. I could not find it even though it is visible at 5.8 magnitude. M13 has hundreds of thousands of stars, and the Arecibo Message was aimed at it. Problem is, by the time the message arrives, M13 will have moved on.
24 M15 - This very dense globular cluster is found in Pegasus.
25 M30 - A globular cluster in the direction of Capricornus.
26 OMEGA CENTAURI (NGC 5139) - The best globular cluster, Omega Centauri is in Centaurus! I observed it at the Southern Skies Star Party on Lake Titicaca. Globular clusters and open clusters are different. Globulars are outside the galactic disk and contain millions of tightly bound stars. Open clusters are inside the disk and contain hundreds of stars loosely bound. Globulars are distant, and that Omega Centauri is seen with the naked eye attests to its size. It is named like a star, Omega being the 24th letter of the Greek alphabet.
27 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. They were fainter than I imagined. They were named after the Portuguese navigator, who saw them on his around the world voyage 1519-22. A supernova appeared in the LMC in 1987. The Milky Way would be awesome from there!
28 SMALL MAGELLANIC CLOUD - The SMC in Toucan has a population of X-ray binaries. It may have been a spiral disturbed by the Milky Way. The Magellanic Clouds are irregular galaxies.
29 ANDROMEDA GALAXY (M31) - M31 is visible to the naked eye, and I spotted it from my parents' back porch. It is a dim smudge 2 stars down and 2 objects up from the square of Pegasus. The Andromeda Galaxy has a trillion stars, so it is more than a smudge. It is the largest galaxy in the Local Group and 2.5 million light-years away. Its spiral shape approaches perfection! If there is no life in M31, there may be none anywhere beyond Earth. Blueshifted M31 and the Milky Way are on a collision course and will merge in 5 billion years to form an elliptical. Imagine walking out on your porch to see M31 cover the sky? It has satellites.
30 PINWHEEL GALAXY (M33) - We look at this face-on spiral and think there must be a Creator. Then, Hawking's "spontaneous creation" comes to mind, the idea that something did come from nothing, that the universe does not need a deity. M33 is in the Local Group and 3 million light-years away. It contains 40 billion stars. It has no central bulge and no black hole.
31 WHIRLPOOL GALAXY (M51) - The Whirlpool is a face-on spiral and the first spiral to be recognized as such. Its curving arms are majestic! It is interacting with NGC 5195. The Whirlpool experiences a high rate of star formation, and a black hole sits at its center.
32 SUNFLOWER GALAXY (M63) - This beauty in Canes Venatici was among the first spiral galaxies to be recognized. A supernova appeared in 1971.
33 BLACKEYE GALAXY (M64) - Named for its dust lane, this spiral resembles a black eye. Its stars orbit clockwise while dust at the rim orbits counterclockwise.
34 BODE'S GALAXY (M81) & CIGAR GALAXY (M82) - These 2 interacted eons ago, and their interaction wreaked havoc with M82. While Bode's Galaxy is a perfect spiral, M82 is shaped like a cigar. It is a starburst galaxy, one whose star formation is extreme.
35 SOMBRERO GALAXY (M104) - This spiral in Virgo passes for a sombrero. There is a central bulge and a prominent dust lane. At magnitude 9, the Sombrero is accessible. An 8-inch telescope resolves the bulge, which hosts a supermassive black hole.
36 M106 - The spiral galaxy in Canes Venatici that helped determine the Hubble constant. There is a supermassive black hole at its center.
37 NGC 1300 - A barred spiral galaxy in Eridanus. A bar extends from both sides of its central bulge.
38 The Mice - These 2 spiral galaxies sideswiped each other millions of years ago and will interact again. In time they will become an elliptical. The long tail gives the impression of a mouse.
39 M60 - A giant elliptical galaxy on the edge of the Virgo Supercluster.
40 M87 - Ellipticals are the largest galaxies, and M87 is huge! It is a source of radio and X-rays and has a supermassive black hole at its center. A black hole this large must result from smaller ones coming together. 12,000 globular clusters orbit M87 compared to 200 orbiting the Milky Way. That globulars are outside the planes of galaxies explains their preservation.