Glowing with a greenish hue below Orion's Belt, the Great nebula in Orion (M42 in the Messier object catalogue, or NGC 1976), is possibly the brightest diffuse nebula visible to the naked eye in the night sky. It is located at a distance of about 1,600 light years from the planet Earth, is 33 light years across, and can be seen clearly through even low-power binoculars, particularly from dark sky locations.
The Orion Nebula contains a very young open cluster, with many stars still in their early years. Observations with powerful telescopes (especially the Hubble Space Telescope) found stars enclosed in dust rings, probably the first phase of a planetary system formation.
More information: Messier 42, SEDS Messier pages