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


Eagle Nebula
diffuse nebula; NGC 6611, M 16

Eskimo Nebula
planetary nebula; NGC 2392

emission nebula
a gas cloud radiating by stimulated emission

Eta Carina
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 Carina; 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.

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 1995 April 6