The Horsehead Nebula lies in the constellation Orion. Part of a big, dark, molecular cloud, it is one of the most recognizable nebulae you can find. The nebula was discovered in the late 1800s, on a photographic plate. The red comes from hydrogen gas behind the nebula. It was ionized by the star Sigma Orionis, which is close by. The thick dust causes the Horsehead Nebula to be so dark. Bright spots in the base of the nebula are actually young stars in the process of forming. It takes approximately 1500 years for light to reach us from the nebula.
Photo : Nigel Sharp (NOAO) KPNO AURA NSF