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"
Infrared Trifid
28/08/1997
The Trifid nebula (M20) is a bright star forming region in Sagittarius, 5000 light years from Earth. In visible light, the interstellar gas cloud is crossed by dark, obscuring dust lanes which roughly divide the glowing emission nebula into three major parts. But the Trifid nebula's well known appearance is dramatically reversed in this infrared view. At longer infrared wavelengths the dust lanes are brighter, radiating more energy than the gas. This image was recorded by the liquid helium cooled Infrared Space Observatory (ISO).