|Right ascension||05h 40m 59s|
|Declination||-02° 27′ 30.0″|
|Type of object||Dark nebula|
|Dimensions||3 x 4 ly|
|Distance from Earth||1,500 ly|
The Horsehead nebula, also known as Barnard 33 or B33, is a dark nebula in the constellation of Orion, the Hunter. It is a dark cloud composed of dust and gas that lies in front of another nebula, IC 434. IC 434 is a bright red/pink nebula composed of ionized hydrogen gas and the Horsehead nebula silhouettes it. The Horsehead nebula is contained within the Orion Molecular Cloud Complex, which also houses several other nebulae such as the Orion nebula. A well known nebula, it is a popular target for astronomers.
The first recording of the nebula was in 1888 by Williamina Flemning on a photographic plate. It was first described by E.E. Barnard in 1913 and Barnard included it in his catalogue in 1919, giving it the designation Barnard 33.
The nebula is in fact a large dark cloud composed of dust and gas that obscures the bright nebula IC 434 behind. The horsehead is actually just the edge of a much larger cloud. However, the full extent of the cloud is not clear in visible light as most of it is against the black background of space. The nebula contains large densities of hydrogen and helium, although over a hundred organic and inorganic gases and large complex organic molecules have been found. The nebula itself is around 2-3 light years across and 3-4 light years high.