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The Triangulum Emission Nebula NGC 604 lies in a spiral arm of Galaxy M33, 2.7 million light-years from Earth. This nebula is a region in which stars are forming.

A nebula (Latin for "mist"; plur. nebulae) is an interstellar cloud of dust and gas. Originally nebula was a catch-all name for any extended astronomical object, including galaxies beyond the Milky Way (some examples of the older usage survive).

Nebulae are classified by how they are illuminated:

• Diffuse nebula are illuminated nebula
  • Emission nebulae are internally illuminated clouds of ionized gas.
  • Reflection nebulae are illuminated by reflections from nearby stars.
• Dark nebulae are unilluminated. They can be detected when they obscure stars or other nebulae.

Nebulae are the birthplace of stars. The dust of the nebula contracts under its own gravitational pull to form new stars. The newly-formed stars can ionize the surrounding gas to produce an emission nebula.

Some nebulae are created by stellar explosions. A star that undergoes the transition to a white dwarf blows off its outer layer to form a planetary nebula. Novas and supernovas can also create nebulae known as nova remnant s and supernova remnantCrab Nebula is an expanding cloud of gas created by the 1054 supernova. 1987A supernova remnant A supernova remnant (SNR) is made up of the materials left behind by the gigantic explosion of a star in a supernova. There are two possible routes to this ends respectively.

See also:

• Solar nebulaIn cosmogony, the solar nebula is a gaseous cloud (or accretion disc), from which, solar systems are formed. This nebular hypothesis was first proposed, in 1755, by Kant; who argued that nebulae slowly rotate, gradually condensing (due to gravity) and fla
• Timeline of the interstellar medium and intergalactic medium
• Crab nebula
• Messier objectThe Messier objects are a set of astronomical objects catalogued by Charles Messier in his catalogue of Nebulae and Star Clusters first published in 1774. The original motivation behind the catalogue was that Messier was a comet hunter, and was frustrated
• Images of nebulae

The Nebula AwardThe Nebula is an award given each year by the Science Fiction and Fantasy Writers of America (SFWA), for the best science fiction stories published in the United States during the two previous years. See rolling eligibility below. There is no cash prize as, annually given out by the Science Fiction and Fantasy Writers of AmericaScience Fiction and Fantasy Writers of America, Inc. was founded in 1965 by Damon Knight. It is a non-profit association of science fiction and fantasy writers, mostly though not entirely in the United States. Membership is limited to professionally publi, are named after nebulae.