Sigma-Clip, Photoshop CS w/ the Fits Liberator plugin, Paint Shop
North is to the left.
At a distance of about 1500 light years, the Horsehead Nebula, in
Orionis, is part of a large dark molecular cloud. Also known as
Barnard 33, the unusual shape was first discovered on a photographic
plate in the late 1800's. The background glow originates from
hydrogen gas predominantly behind the nebula, ionized by the nearby
bright star Sigma Orionis. The darkness of the Horsehead is caused
mostly by thick dust, although the lower part of the Horsehead's
neck casts a shadow to the left.