The Orion nebula, or Messier 42, M42, or NGC 1976, is a diffuse nebula. It is visible to the naked eye in the night sky. It is exceptionally bright because it has O-type stars at its core. They are the hottest and brightest stars. The nebula is south of Orion's Belt in the constellation of Orion.

M42 is 1,344 ± 20 light years away from us. It is the closest region of massive star formation to Earth. Big as it is, the Orion nebula is just part of an even larger star-forming area known as the Orion complex.