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 were seeing.
..1 TRIFID NEBULA (M20) - This 3-lobed nebula has an emission nebula, a reflection nebula & a dark nebula. An emission nebula glows on its own when excited by nearby stars. This is the pink part. A reflection nebula reflects light from stars. This is the blue part. This stellar nursery is above the teapot's spout in Sagittarius.
..2 ORION NEBULA (M42) - Stars are forming in the Orion Nebula, one of the more popular targets in astronomy. We have learned much about how stars form from collapsing clouds of gas and dust. Hubble imaged disks around young stars, suggesting that solar systems are common. Nebulas like M42 form from compressed hydrogen, eventually becoming open clusters. The Trapezium is an open cluster in Orion's sword.
..3 PACMAN NEBULA (NGC 281) - It is called Pacman because the dust cloud gives it 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 Cygnus, its shape is unmistakable. We see the United States and Canada, Mexico and Central America, even Florida and the Gulf of Mexico.
..6 HORSEHEAD NEBULA (Barnard 33) - The Horsehead is a dark nebula in Orion near Alnitak in the 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 enormous 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 its 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 tremendous speed even though we cannot detect movement because it is so far away. A star ended its life as a red giant, leaving behind a white dwarf. The white dwarf illuminates the ring by ultraviolet radiation. 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 its center is magnitude 16.
11 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.
12 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 is burning fuel rapidly and expected to go supernova in a million years. It is classified as 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.
13 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 we 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 resembled a crab.
14 VEIL NEBULA - A supernova remnant whose star exploded, leaving rope-like filaments of gas. The Veil divides into east and west.
15 SNR1572 - Tycho's star in 1572 left this supernova remnant. It is in Cassiopeia and one of 8 supernovas in historical records.
16 BEEHIVE CLUSTER (M44) - This open star cluster in Cancer contains red giants and white dwarfs. It also has main sequence stars, those still fusing hydrogen. I located the Beehive from my parents' yard. The Beehive and Hyades clusters are 700 million years old.
17 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. Aldebaran is unrelated. All stars form in clusters, most of which dissolve after 50 million years. In sky lore, the Hyades and Pleiades were half-sisters.
18 PLEIADES (M45) - The Pleiades is an open cluster. They were 7 sisters to the ancient Greeks. 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.
19 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 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 loosely bound stars. Globulars are distant, and that Omega Centauri can be seen with the naked eye attests to its size. It is named like a star, Omega being the 24th letter of the Greek alphabet.
20 M10 - M10 is a globular cluster in Ophiuchus. It is magnitude 7 and 14,300 light-years distant. M10 was discovered by Charles Messier and resolved into stars by William Herschel.
21 M13 - M13 is the famous globular in Hercules. Edmund Halley found it. 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.
22 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!
23 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.
24 ANDROMEDA GALAXY (M31) - M31 is visible to the naked eye, and I spotted it from my parents' back porch. It appears as a dim smudge 2 stars down and 2 objects up from the square of Pegasus. The Andromeda Galaxy contains 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. Can you imagine walking out on your porch to see M31 cover the sky? M31 has satellites.
25 TRIANGULUM GALAXY (M33) - This face-on spiral is called the Pinwheel. We look at it and think there must be a Creator. Then, Hawking's "spontaneous creation" comes to mind, the realization that something did indeed 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. There is no central bulge and no black hole.
26 WHIRLPOOL GALAXY (M51) - The Whirlpool is a face-on spiral and the first spiral to be recognized as such. It is interacting with NGC 5195. The Whirlpool experiences a high rate of star formation, and a black hole sits at its center. Its curving arms are majestic!
27 SUNFLOWER GALAXY (M63) - This beauty in Canes Venatici was among the first spiral galaxies to be recognized. A supernova appeared in 1971.
28 BLACKEYE GALAXY (M64) - Named for its dust lane, this spiral looks like a black eye. Its stars orbit clockwise while the dust at its rim orbits counterclockwise.
29 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 cigar-shaped. It is a starburst galaxy, one in which star formation is extreme.
30 M60 - A giant elliptical galaxy on the edge of the Virgo Supercluster.
31 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 lie outside the planes of galaxies explains their preservation.
32 SOMBRERO GALAXY (M104) - This spiral in Virgo passes for a sombrero. It has 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.