ETYM Latin, mist, cloud; akin to German nebel mist, Old High Germ. nebul, Dutch nevel, Skr. nabhas cloud, mist. Related to Nebule.
Vast gaseous area of universe.
Cloud of gas and dust in space. Nebulae are the birthplaces of stars, but some nebulae are produced by gas thrown off from dying stars (see planetary nebula; supernova). Nebulae are classified depending on whether they emit, reflect, or absorb light.
An emission nebula, such as the Orion nebula, glows brightly because its gas is energized by stars that have formed within it. In a reflection nebula, starlight reflects off grains of dust in the nebula, such as surround the stars of the Pleiades cluster. A dark nebula is a dense cloud, composed of molecular hydrogen, which partially or completely absorbs light behind it. Examples include the Coalsack nebula in Crux and the Horsehead nebula in Orion.
An immense cloud of gas (mainly hydrogen) and dust in interstellar space.