Changes

==Properties and Structure==

==Properties and Structure==

At 1,600 [[light year]]s away, the nebula's apparent size of over 20° corresponds to a physical size of at least 582 light years.<ref>By direct calculation using values given here.</ref> The segment that is visisible is believed to be part of a larger shell of material, with only the easternmost segment being visible in optical light.<ref name=arxiv>O'Dell, C., Ferland, G., Porter, R. and van Hoof, P. (2011). Physical Conditions in Barnard’S 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. [https://arxiv.org/abs/1103.2789 arXiv:1103.2789]</ref> The nebula is expanding at around 15-23 km/s.<ref name=arxiv/> The nebula contains several O and B [[Stellar Classifications|type]] [[star]]s.

At 1,600 [[light year]]s away, the nebula's apparent size of over 20° corresponds to a physical size of at least 582 light years.<ref>By direct calculation using values given here.</ref> 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.<ref name=arxiv>O'Dell, C., Ferland, G., Porter, R. and van Hoof, P. (2011). Physical Conditions in Barnard’S 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. [https://arxiv.org/abs/1103.2789 arXiv:1103.2789]</ref> The nebula is expanding at around 15-23 km/s.<ref name=arxiv/> The nebula contains several O and B [[Stellar Classifications|type]] [[star]]s.

Even this nebula may be the inner surface of an even larger nebula that is at least 30 degrees in diameter.<ref>[http://www.daviddarling.info/encyclopedia/B/Barnards_Loop.html Barnard's Loop] from daviddarling.info</ref> As only the inner suface is [[ionization|ionized]], only this is visible. The enveloping nebula would be truly vast and comprise of very hot, low [[density]] [[gas]].<ref name=seds/> Observations of the nebula in [[ultraviolet|ultraviolet light]] have suggested the existence of this larger nebula.

Even this nebula may be the inner surface of an even larger nebula that is at least 30 degrees in diameter.<ref>[http://www.daviddarling.info/encyclopedia/B/Barnards_Loop.html Barnard's Loop] from daviddarling.info</ref> As only the inner suface is [[ionization|ionized]], only this is visible. The enveloping nebula would be truly vast and comprise of very hot, low [[density]] [[gas]].<ref name=seds/> Observations of the nebula in [[ultraviolet|ultraviolet light]] have suggested the existence of this larger nebula.