| Emission nebula | |
|---|---|
| H II region | |
 Barnard's Loop can be seen on this image as a diffuse red semicircle. | |
| Observation data:J2000epoch | |
| Right ascension | 05h 27.5m |
| Declination | −03° 58′ |
| Distance | either 518 or 1434 ly |
| Apparent magnitude (V) | 5 |
| Apparent dimensions (V) | 10° |
| Constellation | Orion |
| Physical characteristics | |
| Radius | either 50 or 150 ly |
| Designations | Sh 2-276 |
| See also:Lists of nebulae | |
Barnard's Loop (catalogue designationSh 2-276) is anemission nebula in theconstellation ofOrion. It is part of theOrion molecular cloud complex which also contains the darkHorsehead and brightOrion nebulae. The loop takes the form of a large arc 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 10° as seen from Earth, covering much of Orion. It is best seen in long-exposure photographs, although observers under very dark skies may be able to see it with the naked eye.
It is about 440 parsecs (1,400 ly) away and 110 parsecs (360 ly) in length.[1][2] It is thought to have originated in asupernova explosion about 2 million years ago, which may have also created several knownrunaway stars, includingAE Aurigae,Mu Columbae and53 Arietis, which are believed to have been part of a multiple star system in which one component exploded as a supernova.[3]
Although this faint nebula was certainly observed by earlier astronomers, it is named after the pioneeringastrophotographerE. E. Barnard who photographed it and published a description in 1894.[4]
