(catalogue designation Sh 2-276
) is an emission nebula
in the constellation
. It is part of a giant molecular cloud
which also contains the bright Horsehead
nebulae. The loop takes the form of a large arc
centred 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
It is estimated to lie at a distance of approximately 1600 light years
, giving it actual dimensions of about 300 light years across. It is thought to have originated in a supernova
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 thought 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
who photographed it and published a description in 1894.
<gallery>Image:Nebula-Barnard's-Loop-bw-inverse.jpeg|Above photo of Barnard's Loop nebula in inverted black and white of the red channel; the loop can now be seen... Read More