IC 434

{{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 =

| type = emission

| type2 =

| epoch = J2000

| subtype = H II region

| class =

| constellation = Orion

| ra = {{RA|05|40.9}}

| dec = {{DEC|−02|27}}

| dist_ly = {{cvt|385|pc|ly|order=flip}}

| dist_pc =

| dist_z =

| appmag_v = 4.5

| appdia =

| size_v = {{val|60|×|40|ul=arcminute}}

| radius_ly =

| radius_pc =

| dimensions =

| absmag_v =

| notes =

| names =

}}

IC 434 is a bright emission nebula in the equatorial constellation of Orion. It was discovered on February 1, 1786, by German-British astronomer William Herschel. 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}}.

This is an H II region that is being ionized by 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=~ }} The mass displaced by the advancing ionization front of IC 434 is estimated at {{val|e=4|u=Solar mass}}. The nebula includes dust with an estimated mass of {{val|2.3|u=Solar mass}}.

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. 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.