A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z.


30 Doradus Nebula
diffuse nebula; NGC 2070, Tarantula Nebula


a star, within a nebula near Rho Ophiuchus


Barnard 33
dark nebula; Horsehead Nebula

The Blue Snowball
planetary nebula; NGC 7662


Cat's Eye Nebula
planetary nebula; NGC 6543

celestial equator
the projection onto the sky of the Earth's equator

Checkmark Nebula
diffuse nebula; NGC 6618, M 17

Clownface Nebula
planetary nebula; NGC 2392, Eskimo Nebula

Crab Nebula
supernova remnant; NGC 1952, M 1; a supernova remnant

Cygnus Loop
supernova remnant; Veil Nebula


dark nebula
a dust cloud blocking the light from behind

abbreviation of Declination, which along with Right Ascension determines a position on the sky. Declination is measured north (+) and south (-) from the celestial equator and specified in degrees and minutes.

diffuse nebula
an emission or reflection nebula

Dumbbell Nebula
planetary nebula; NGC 6853, M 27

micron-size solid particles of somewhat uncertain composition, probably carbon, iron or silicates.

For more info about dust and its role in nebulae see Dust Evolution in the Universe by Amara Graps.


Eagle Nebula
diffuse nebula; NGC 6611, M 16

Eskimo Nebula
planetary nebula; NGC 2392

emission nebula
a gas cloud radiating by stimulated emission

Eta Carinae
a massive star within NGC 3372

having detectably non-zero angular size, not star-like



galactic cluster
a loose cluster of a small number of stars; aka open cluster

an "island universe" of billions of stars

globular cluster
a dense cluster of stars

The Ghost of Jupiter
planetary nebula; NGC 3242


Helix Nebula
planetary nebula; NGC 7293

Homunculus Nebula
gas expelled from Eta Carinae; part of NGC 3372

Horsehead Nebula
dark nebula; Barnard 33. Nearby are IC 434, NGC 2023 and NGC 2024.

Horseshoe Nebula
diffuse nebula; NGC 6618, M 17

Hourglass Nebula
dark nebula; NGC 6523, M 8, part of Lagoon Nebula


IC 434
diffuse nebula; associated with the Horsehead Nebula



Keyhole Nebula
dark nebula; NGC 3324; part of NGC 3372


Lagoon Nebula
diffuse nebula; NGC 6523, M 8, contains Hourglass Nebula

Little Dumbbell Nebula
planetary nebula; NGC 650-1, M 76

abbreviation for light-year (about 6,000,000,000,000 miles)


Charles Messier was a French comet hunter. His catalog (first published in 1781) of nebulous objects was originally intended as a list of "junk" to avoid when searching for comets. (more info)

M 1
supernova remnant; NGC 1952, Crab Nebula

M 8
diffuse nebula; NGC 6523, Lagoon Nebula

M 16
diffuse nebula; NGC 6611, Eagle Nebula

M 17
diffuse nebula; NGC 6618, Omega Nebula

M 20
diffuse nebula; NGC 6514, Trifid Nebula

M 27
planetary nebula; NGC 6853, Dumbbell Nebula

M 42
diffuse nebula; NGC 1976, the main part of Orion Nebula

M 43
diffuse nebula; NGC 1982, a smaller part of Orion Nebula

M 45
diffuse nebula Pleiades, Subaru, Seven Sisters

M 57
planetary nebula; NGC 6720, Ring Nebula

M 76
planetary nebula; NGC 650-1, Little Dumbbell Nebula


any of various types of extended objects in the sky; also see individual names

the plural form of "nebula"; "nebulas" is also correct, but not as cool.

New General Catalogue, compiled by J. L. E. Dreyer in 1888; later amended by the two Index Catalogues (IC)

NGC 0650-1
planetary nebula; M 76, Little Dumbbell Nebula

NGC 1952
supernova remnant; M 1, Crab Nebula

NGC 1976
diffuse nebula; M 42, the main part of the Orion Nebula

NGC 1982
diffuse nebula; M 43, a smaller part of Orion Nebula

NGC 2070
diffuse nebula; Tarantula Nebula, 30 Doradus Nebula

NGC 2237
diffuse nebula; NGC 2244, Rosette Nebula

NGC 2244
an open cluster near NGC 2237, Rosette Nebula

NGC 2392
planetary nebula; Eskimo Nebula

NGC 2440
planetary nebula

NGC 3242
planetary nebula; The Ghost of Jupiter

NGC 3324
dark nebula; Keyhole Nebula; part of NGC 3372

NGC 3372
diffuse nebula; Eta Carina Nebula, Keyhole Nebula, Homunculus Nebula

NGC 6514
diffuse nebula; M 20, Trifid Nebula

NGC 6523
diffuse nebula; M 8, Lagoon Nebula, contains Hourglass Nebula

NGC 6543
planetary nebula; Cat's Eye Nebula

NGC 6611
diffuse nebula; M 16, Eagle Nebula

NGC 6618
diffuse nebula; M 17, Omega Nebula

NGC 6720
planetary nebula; M 57, Ring Nebula

NGC 6853
planetary nebula; M 27, Dumbbell Nebula

NGC 6960
part of Veil Nebula, supernova remnant;

NGC 7009
planetary nebula; Saturn Nebula

NGC 7023
diffuse nebula

NGC 7293
planetary nebula; Helix Nebula

NGC 7662
planetary nebula; The Blue Snowball


an old star is very old indeed, about 10 billion years (or more)

Omega Nebula
diffuse nebula; NGC 6618, M 17

open cluster
a loose cluster of a small number of stars; aka galactic cluster

Orion Nebula
diffuse nebula; M 42 (NGC 1976) and M 43 (NGC 1982)


planetary nebula
a bright nebula thrown off by a dying star

diffuse nebula; M 45, Subaru, Seven Sisters

Puppis A
a supernova remnant



abbreviation of Right Ascension which along with Declination defines a position in the sky. RA is measured eastward along the celestial equator with the zero point at the vernal equinox; it is specified in hours, minutes and seconds (seconds omitted here)

reflection nebula
a dust cloud reflecting starlight

Rho Ophiuchus
a star, within a nebula near Antares

Ring Nebula
planetary nebula; NGC 6720, M 57

Rosette Nebula
diffuse nebula; NGC 2237, NGC 2244


Saturn Nebula
planetary nebula; NGC 7009

Seven Sisters
diffuse nebula; M 45, Pleiades, Subaru, Seven Sisters

supernova remnant
leftover gas from a supernova explosion

stellar classification
Stars given a designation consisting of a letter and a number according to the nature of their spectral lines which corresponds roughly to surface temperature. The classes are: O, B, A, F, G, K, and M; O stars are the hottest; M the coolest. The numbers are simply subdivisions of the major classes. The classes are oddly sequenced because they were assigned long ago before we understood their relationship to temperature. O and B stars are rare but very bright; M stars are numerous but dim. The Sun is designated G2.

diffuse nebula; M 45, Pleiades, Seven Sisters

Supernova 1987A
a very new supernova remnant

Swan Nebula
diffuse nebula; NGC 6618, M 17


Tarantula Nebula
diffuse nebula; NGC 2070, 30 Doradus Nebula

a four-star system at the heard of the Orion Nebula

Trifid Nebula
diffuse nebula; NGC 6514, M 20



Veil Nebula
a supernova remnant; contains NGC 6960, 6979, 6992 6995; Cygnus Loop

Vela SNR
a supernova remnant




"young" for a star must be interpreted in the context of the average stellar lifetime of billions of years. A young star is one that is no more than a few million years old.


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Bill Arnett 1997 Feb 10