The Horsehead Nebula in Orion.

One of the most identifiable nebulae in the sky, the Horsehead Nebula in Orion , 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 1800s. The red glow originates from hydrogen gas predominantly behind the nebula, ionized by the nearby bright star Sigma Orionis . A blue reflection nebula dubbed NGC 2023 surrounds the bright star at the lower left. 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 . Light takes about 1500 years to reach us from the Horsehead Nebula . The above image was taken earlier this month with a 0.6-meter telescope at the Mt. Lemmon SkyCenter in Arizona , USA .