It is a dark nebula in the constellation Orion, located just south of the star Alnitak, and is part of the much larger Orion Molecular Cloud Complex, 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 bears some resemblance to 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. Bright spots in the Horsehead Nebula’s base are young stars just in the process of forming.
Nebulae, from the Greek word for “cloud,” are made of gas and tiny dust particles enclosed in shells of nitrogen and carbon monoxide ice. The temperature of a nebula is about 10 degrees K. This temperature is so cold that scientists speculate that the nebula will eventually collapse in on itself, and the pressures generated will begin the ignition of proto-stars.