IC 434

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.^[2] The nebula is located at a distance of approximately 1,260 ly (385 pc) from the Sun and spans the interior of a neutral hydrogen shell with an angular size of 2° × 4°. At that distance, the dimensions correspond to a projected size of 42 ly × 85 ly (13 pc × 26 pc).^[2]

IC 434

Emission nebula
IC 434 is found behind the Horsehead Nebula
Observation data: J2000 epoch
Subtype	H II region
Right ascension	05h 40.9m [1]
Declination	−02° 27′[1]
Distance	1,260 ly (385 pc)[2] ly
Apparent magnitude (V)	4.5[1]
Apparent dimensions (V)	60′ × 40′[1]
Constellation	Orion
See also: Lists of nebulae

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 13 ly (4 pc) and a mass of around ~ 100 M_☉ The mass displaced by the advancing ionization front of IC 434 is estimated at 10⁴ M_☉.^[3] The nebula includes dust with an estimated mass of 2.3 M_☉.^[2]

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.^[2] 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.^[3]