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"
NGC 6992: A Glimpse of the Veil
28/09/2001
After 5,000 years, the gorgeous Veil Nebula is still turning heads. Cataloged as NGC 6992, these glowing filaments of interstellar shocked gas are part of a larger spherical supernova remnant known as the Cygnus Loop or the Veil Nebula -- expanding debris from a star which exploded over 5,000 years ago. This color digital image of a bit of the Veil has been processed and enhanced to reveal stunning details in the diaphanous cosmic cloud. Seen from our perspective against a rich Milky Way star field, the Veil Nebula is now known to lie some 1,400 light-years away toward the constellation Cygnus. At that distance, witnesses to the original stellar explosion would have seen a star in the heavens increase in brightness to about -8 magnitude, roughly corresponding to the brightness of the crescent Moon.