Orion Nebula

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Orion Nebula,

bright diffuse nebulanebula
[Lat.,=mist], in astronomy, observed manifestation of a collection of highly rarefied gas and dust in interstellar space. Prior to the 1960s this term was also applied to bodies later discovered to be galaxies, e.g.
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 in the constellation Orion; also known as the Great Nebula of Orion and cataloged as M42 or NGC 1976. It is located near the middle of the "sword" hanging from Orion's "belt" of stars. Its central bright region is about 1° in diameter and it has a total extension of 3°. It is about 1,000 light-years distant and as many as 60 light-years in diameter. The nebula is an enormous cloud of gas surrounding a cluster of very hot young stars. To the naked eye the nebula appears to be a faint star but becomes a vague patch of light when viewed through binoculars. The bright region is divided into two sections, the northeast portion being cataloged separately as M43 or NGC 1982. The Orion Nebula is the nearest major site to earth of massive star formation.
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Orion nebula

(M42; NGC 1976) One of the brightest emission nebulae in the sky, about 400 parsecs distant. It is just visible to the naked eye as a diffuse luminous patch, 1° across, in the center of Orion's Sword; M43 (NGC 1982) is a small northern part of M42, a dust lane separating them. The Orion nebula is a complex region of ionized hydrogen (an H II region) that is associated with the Orion molecular cloud (OMC-1), part of a system of giant molecular clouds in the Orion constellation. The Orion nebula is centered on a very dense stellar cluster – the Trapezium cluster – containing four hot young stars that excite and ionize the nebula, so producing both radio and optical radiation. Their total luminosity is about 3 × 105 times that of the Sun. The nebula is also a source of X-rays. The region is one of active star formation, containing T Tauri stars, maser sources, Herbig–Haro objects, the BN object, and the Kleinmann-Low nebula. The interface between the nebula and the adjacent molecular cloud is an example of a photodissociation region.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Orion Nebula


a very large gas-dust cloud, the closest nebula to our solar system.

Located about 300 parsecs from our solar system, the Orion nebula is visible in the constellation Orion on moonless winter nights as a pale, twinkling spot. It measures about 5.5 parsecs in diameter. At its center is a small cluster of stars, among which is the Trapezium, which comprises four physically linked, hot, bright stars. Ultraviolet light from these stars causes the gas in the nebula—consisting primarily of hydrogen—to glow. The dust in the Orion Nebula absorbs light, which is partially responsible for the nebula’s wispy appearance.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

Orion Nebula

[ə′rī·ən ′neb·yə·lə]
A luminous cloud surrounding Ori, the northern star in Orion's dagger; visible to the naked eye as a hazy object. Also known as Great Nebula of Orion.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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