The Horsehead Nebula

The Horsehead Nebula (also known as Barnard 33 in emission nebula IC 434)

The Horsehead Nebula (also known as Barnard 33 in emission nebula IC 434) is a dark nebula in the constellation Orion. The nebula is located just to the south of the star Alnitak, which is farthest east on Orion's Belt, and is part of the much larger Orion Molecular Cloud Complex. The nebula was first recorded in 1888 by Williamina Fleming on photographic plate B2312 taken at the Harvard College Observatory. The Horsehead Nebula is approximately 1500 light years from Earth. It is one of the most identifiable nebulae because of the shape of its swirling cloud of dark dust and gases, which is similar to that of a horse's head when viewed from Earth.

The red or pinkish 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. Streams of gas leaving the nebula are funneled by a strong magnetic field. Bright spots in the Horsehead Nebula's base are young stars just in the process of forming. The nebula exhibits a noticeable change in the density of the stars which indicates that a red ribbon of radiant red hydrogen gas at the precipice of a sizable dark cloud. The underside of the horse’s visible ‘neck’ reflects this concept of shade and density because it casts a great shadow across the field of view just below the horse’s ‘muzzle’. The visible heart of the nebula emerges from the gaseous complex to serve as an active site of the formation of “low-mass” stars. A glowing strip of hydrogen gas marks the edge of the massive cloud and noticeable densities of stars are present on either side. The dark cloud of dust and gas is a region in the Orion Nebula where star formation is taking place right now. A complex housing forming stars, known as a stellar nursery, can contain over 100 known organic and inorganic gases as well of dust consisting of large and complex organic molecules. The region of the Orion Nebula containing the Horsehead is a stellar nursery. The darkness of the massive nebula is not explained by this dust and gas, but by the complex blocking the light of stars behind it.The heavy concentrations of dust in the Horsehead Nebula region and neighbouring Orion Nebula are localized, resulting in sections of almost complete transparency.