Astrophysics (Index)About


(cloud of dust and gas)

The term nebula is currently used for a cloud of gas and dust. A general classification according to their visible appearance divides them into bright nebulae versus dark nebulae. A dark nebula includes dust blocking any light from behind, often a star-forming region. A bright nebula may be a reflection nebula, essentially what would be a dark nebula, but is reflecting light from a nearby source (e.g., star) or a bright nebula may be an emission nebula, emitting light itself, such as an HII region. Planetary nebulae and supernova remnants are also nebulae that emit light. The term diffuse nebula is used for those without distinct boundaries.

The term nebula was coined for (stationary) fuzzy objects, i.e., things that appear quite different from stars, planets, the Moon, comets (which move), or the Sun. This included distant groups of stars, e.g., stellar clusters and galaxies. The name may still be used occasionally for stellar clusters, but use of the term for galaxies is now virtually gone, even though it was formerly the ordinary term for them (before they were considered to be galaxies), a usage that is still seen in historical writing, such as references to Andromeda as the Great Andromeda Nebula, and the Messier Catalog's original name, Catalogue of Nebulae and Star Clusters.

The word nebula is also used within some phrases that indicate particular kinds of "fuzzy" objects, such as planetary nebulae and protoplanetary nebulae.

(object type,cloud type)
Further reading:

Referenced by pages:
bright nebula
Caldwell Catalog
Cederblad Catalog (Ced)
infrared cirrus
cosmic dust
Cygnus Loop
dark nebula
diffuse emission
emission-line star
emission nebula
galaxy cloud
Atlas of Galactic Nebulae (GN)
Herbig-Haro object (HH)
HII region (HII)
Index Catalog (IC)
interstellar astrophysics
Kapteyn universe
Lynds Catalog of Dark Nebulae (LDN)
Crab Nebula (M1)
Andromeda (M31)
MASH Catalog of Planetary Nebulae
Messier Catalog (M)
molecular cloud
near infrared (NIR)
nebular hypothesis
New General Catalogue (NGC)
Spindle Galaxy (NGC 5866)
Orion Nebula Cluster (ONC)
Orion Nebula (M42)
Parsamian Nebula Catalog
passive dust
planet formation
pre-main-sequence star (PMS)
planetary nebula (PN)
planetary nebula luminosity function (PNLF)
point source
protoplanetary nebula (PPN)
pulsar wind nebula (PWN)
rare designator prefixes
reflection nebula
Sharpless Catalog (Sh2)
supernova remnant (SNR)
solar nebula
solid angle (Ω)
star cloud
surface brightness (SB)
Taurus Molecular Cloud 1 (TMC-1)
Trapezium Cluster
T Tauri
Vela supernova remnant
VLT-FLAMES Tarantula Survey (VFTS)
Westerhout Radio Survey (W)
William Herschel Telescope (WHT)
WR 104
Zanstra method