Glossary

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

dust

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

E

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

extended

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

F

G

galactic cluster

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

galaxy

an "island universe" of billions of stars

globular cluster

a dense cluster of stars

The Ghost of Jupiter

planetary nebula; NGC 3242

H

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

I

IC 434

diffuse nebula; associated with the Horsehead Nebula

J

K

Keyhole Nebula

dark nebula; NGC 3324; part of NGC 3372

L

Lagoon Nebula

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

Little Dumbbell Nebula

planetary nebula; NGC 650-1, M 76

ly

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

M

Messier

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

N

Nebula

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

Nebulae

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

NGC

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

O

old

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)

P

planetary nebula

a bright nebula thrown off by a dying star

Pleiades

diffuse nebula; M 45, Subaru, Seven Sisters

Puppis A

a supernova remnant

Q

R

RA

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

S

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.

Subaru

diffuse nebula; M 45, Pleiades, Seven Sisters

Supernova 1987A

a very new supernova remnant

Swan Nebula

diffuse nebula; NGC 6618, M 17

T

Tarantula Nebula

diffuse nebula; NGC 2070, 30 Doradus Nebula

Trapezium

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

Trifid Nebula

diffuse nebula; NGC 6514, M 20

U

V

Veil Nebula

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

Vela SNR

a supernova remnant

W

X

Y

young

"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.

Z

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1995 April 6