Nebula
A nebula is a giant cloud of gas (mostly hydrogen and helium) and cosmic dust situated between stars in the interstellar medium. Nebulae serve as sites of stellar birth and death—including emission nebulae that glow from ionized gas, reflection nebulae that scatter starlight, and dark nebulae that obscure background stars.
Source: science.nasa.gov
APODs including "Nebula"
Orion on Film
07/02/2003
Orion, the Hunter, is one of the most easily recognizable constellations in planet Earth's night sky. But Orion's stars and nebulae don't look quite as colorful to the eye as they do in this lovely photograph, taken last month from Vekol Ranch south of Phoenix, Arizona, USA. The celestial scene was recorded in a five minute time exposure using high-speed color print film and a 35mm camera mounted on a small telescope. In the picture, cool red giant Betelgeuse takes on a yellowish tint as the brightest star at the upper left. Otherwise Orion's hot blue stars are numerous, with supergiant Rigel balancing Betelgeuse at the lower right, Bellatrix at the upper right, and Saiph at the lower left. Lined up in Orion's belt (left to right) are Alnitak, Alnilam, and Mintaka all about 1,500 light-years away, born of the constellation's well studied interstellar clouds. And if the middle "star" of Orion's sword looks reddish and fuzzy to you, it should. It's the stellar nursery known as the Great Nebula of Orion.