The Orion Nebula (also known as Messier 42, M42 or NGC 1976) is a diffuse nebula in the Milky Way located south of the Orion Belt in the constellation Orion. It is one of the brightest nebulae and visible to the naked eye. M42 is about 1,350 light years away from the Earth and is therefore one of the nearest HII star formation regions. The diameter of the Orion Nebula is estimated at 24 light years. Its mass is approximately 2,000 time the Sun.

The Orion Nebula is one of the most studied and photographed objects in the night sky and one of the most intensively studied celestial bodies. The nebula provided important insights into the process of the formation of stars and planetary systems from collapsing gas and dust clouds. Astronomers have also observed protoplanetary discs, brown dwarfs and turbulent movements of gas in the nebula.