Barnard's Loop (catalogue designation Sh 2-276) is an emission nebula in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

of Orion. It is part of the Orion molecular cloud complex which also contains the dark Horsehead and bright Orion nebulae. The loop takes the form of a large

arc ARC may refer to: Business * Aircraft Radio Corporation, a major avionics manufacturer from the 1920s to the '50s * Airlines Reporting Corporation, an airline-owned company that provides ticket distribution, reporting, and settlement services * ...

centered approximately on the Orion Nebula. The stars within the Orion Nebula are believed to be responsible for ionizing the loop. The loop extends over about 600 arcminutes as seen from Earth, covering much of Orion. It is well seen in long-exposure photographs, although observers under very dark skies may be able to see it with the naked eye. Recent estimates place it at a distance of either 159 pc (518

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s) or 440 pc (1434 ly) giving it dimensions of either about 100 or 300 ly across respectively. It is thought to have originated in a

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

explosion about 2 million years ago, which may have also created several known runaway stars, including AE Aurigae, Mu Columbae and 53 Arietis, which are believed to have been part of a multiple star system in which one component exploded as a supernova. Although this faint nebula was certainly observed by earlier astronomers, it is named after the pioneering astrophotographer

E. E. Barnard Edward Emerson Barnard (December 16, 1857 – February 6, 1923) was an American astronomer. He was commonly known as E. E. Barnard, and was recognized as a gifted observational astronomer. He is best known for his discovery of the high proper mo ...

who photographed it and published a description in 1894. Image:Nebula-Barnard's-Loop-bw-inverse.jpeg, Above photo of Barnard's Loop nebula in inverted black and white of the red channel Image:Nebula-Barnard's-Loop.jpeg, Long exposure of Orion with red clouds of ionized hydrogen (H-alpha). The big bow on the left is Barnard's Loop. Image:Orion Head to Toe.jpg, Barnard's Loop seen against the major stars and nebula of Orion

References

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External links

Photograph identifying several nebulae in Orion
* ttp://apod.nasa.gov/apod/ap120312.html The Scale of the Universe( Astronomy Picture of the Day 12 March 2012) {{Sh2 objects H II regions Orion molecular cloud complex Sharpless objects Discoveries by Edward Emerson Barnard