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"
Elusive Jellyfish Nebula
08/04/2004
Normally faint and elusive, the Jellyfish Nebula is caught in the net of this spectacular wide-field telescopic view. Flanked by two yellow-tinted stars at the foot of a celestial twin - Mu and Eta Geminorum - the Jellyfish Nebula is the brighter arcing ridge of emission with dangling tentacles just right of center. Here, the cosmic jellyfish is seen to be part of bubble-shaped supernova remnant IC 443, the expanding debris cloud from an exploded star some 5,000 light-years away. Also in view, emission nebula IC 444 nearly fills the field to the upper left, dotted with small blue reflection nebulae. Like its cousin in astrophysical waters, the Crab Nebula, IC 443 is known to harbor a neutron star, the collapsed core of the massive star that exploded over 30,000 years ago.