The Horsehead nebula (also called Barnard 33) is part of a massive, dark molecular cloud, located in the constellation of Orion. The nebula glows red as hydrogen gas is emitted by Sigma Orionis, which is located behind the Horsehead. A blue glow is also behind the nebula, coming from a reflection nebula called NGC 2023. Reflection nebulas give off light because they reflect the light of a nearby star. In the midst of the red and blue glow, the Horsehead shape is formed in a dark, black cloud of dust. Interstellar dust blocks out light, leaving the appearance of a dark hole in the nebula. Light from the Horsehead nebula takes approximately 1,500 years to reach Earth.
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| Great Orion Nebula in bottom right and Horsehead nebula in top left. |
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