Barnard's loop
Barnard's loop (Sharpless 276, part of the Orion-Eridanus Bubble) is a diffuse nebula in the constellation of Orion, the hunter.[2] The nebula was discovered by E. E. Barnard in 1895 utilising long exposure photographic methods.[3] However it may have been observed by William Herschel, one of the great nebula discoverers, in February 1786.[2] Unsurprisingly it is therefore far too faint to be observed with the naked eye. The nebula can be seen as a ring of bright gas surrounding Orion's belt. The Orion nebula along with the famous horsehead nebula are situated within Barnard's loop.
| Barnard's loop | |
|---|---|
| |
| Observational Data | |
| Designation | Sharpless 276 |
| Right ascension | 05h 27m 30s[1] |
| Declination | -03° 58â² 00â³[1] |
| Constellation | Orion |
| Type of object | Diffuse nebula |
| Dimensions | >20°[2] |
| Astrometry | |
| Distance from Earth | 1,600 ly[2] |
Properties and Structure
At 1,600 light years away, the nebula's apparent size of over 20° corresponds to a physical size of at least 582 light years.[4] The segment that is visible is believed to be part of a larger shell of material, with only the easternmost segment being visible in optical light.[5] The nebula is expanding at around 15-23 km/s.[5] The nebula contains several O and B type stars.
Even this nebula may be the inner surface of an even larger nebula that is at least 30 degrees in diameter.[6] As only the inner suface is ionized, only this is visible. The enveloping nebula would be truly vast and comprise of very hot, low density gas.[2] Observations of the nebula in ultraviolet light have suggested the existence of this larger nebula.
References
- â 1.0 1.1 Barnard's Loop from the SIMBAD Astronomical Database
- â 2.0 2.1 2.2 2.3 2.4 Barnard's loop from messier.seds.org
- â Barnard's Loop Around Orion from apod.nasa.gov
- â By direct calculation using values given here.
- â 5.0 5.1 O'Dell, C., Ferland, G., Porter, R. and van Hoof, P. (2011). Physical Conditions in BarnardâS Loop, Components of the Orion-Eridanus Bubble, and Implications for the Warm Ionized Medium Component of the Interstellar Medium. The Astrophysical Journal, 733(1), p.9. arXiv:1103.2789
- â Barnard's Loop from daviddarling.info