Editing IC 434 (section)

{{Short description|Emission nebula in the constellation Orion}}
{{Infobox nebula
 | name          = IC 434
 | image         = Barnard 33.jpg
 | image_scale   = 1.3
 | alt           = 
 | caption       = IC 434 is found behind the [[Horsehead Nebula]]
 | credit        = <!-- Per MOS:CREDITS, credits are discouraged -->
 | type          = emission
 | type2         = <!-- can be wikilinked -->
 | epoch         = [[J2000]]
 | subtype       = H II region
 | class         = 
 | constellation = [[Orion (constellation)|Orion]]
 | ra            = {{RA|05|40.9}}<ref name=Ruben_2009/>
 | dec           = {{DEC|−02|27}}<ref name=Ruben_2009/>
 | dist_ly       = {{cvt|385|pc|ly|order=flip}}<ref name=Ochsendorf_Tielens_2015/>
 | dist_pc       = 
 | dist_z        = 
 | appmag_v      = 4.5<ref name=Ruben_2009/>
 | appdia        = <!-- dd°mm'ss".mas -->
 | size_v        = {{val|60|×|40|ul=arcminute}}<ref name=Ruben_2009/>
 | radius_ly     = 
 | radius_pc     = 
 | dimensions    = 
 | absmag_v      = 
 | notes         = 
 | names         = 
}}

'''IC 434''' is a bright [[emission nebula]] in the equatorial [[constellation]] of [[Orion (constellation)|Orion]]. It was discovered on February 1, 1786, by German-British astronomer [[William Herschel]].<ref name=Ochsendorf_Tielens_2015/> The nebula is located at a distance of approximately {{cvt|385|pc|ly|order=flip}} from the Sun and spans the interior of a [[neutral hydrogen]] shell with an [[angular size]] of {{val|2|×|4|u=°}}. At that distance, the dimensions correspond to a projected size of {{cvt|13|×|26|pc|ly|order=flip}}.<ref name=Ochsendorf_Tielens_2015/>

This is an [[H II region]] that is being [[Ionization|ionized]] by [[Ultraviolet astronomy|ultraviolet]] radiation from the nearby [[Sigma Orionis]] (σ Ori) multi-star system. An additional half dozen stars provide further illumination of IC 434. This H II region is one of the youngest to form around members of the [[Orion OB1]] association of hot stars. The region has a radius of about {{cvt|4|pc|ly|order=flip}} and a mass of around {{val|100|ul=Solar mass|p=~&nbsp;}} The mass displaced by the advancing ionization front of IC 434 is estimated at {{val|e=4|u=Solar mass}}.<ref name=Bally_et_al_2018/> The nebula includes [[Cosmic dust|dust]] with an estimated mass of {{val|2.3|u=Solar mass}}.<ref name=Ochsendorf_Tielens_2015/>

IC 434 is surrounded by a shell of neutral hydrogen gas with the identifier GS206-17+13. The primary driving energy behind this expanding shell was likely supplied by the blue supergiant [[Epsilon Orionis]].<ref name=Ochsendorf_Tielens_2015/> The [[Horsehead Nebula]] is a [[dark nebula]] that is silhouetted against the diffuse background of IC 434. It is protruding from the Orion B [[molecular cloud]], which is part of the [[Orion molecular cloud complex]].<ref name=Bally_et_al_2018/>