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"
Sharpless 308
23/04/2009
Blown by fast winds from a hot, massive star, this cosmic bubble is huge. Cataloged as Sharpless 308 it lies some 5,200 light-years away in the constellation Canis Major and covers over 2/3 degree on the sky (compared with 1/2 degree for the Full Moon). That corresponds to a diameter of 60 light-years at its estimated distance. The massive star itself, a Wolf-Rayet star, is the bright blue one near the center of the nebula. Wolf-Rayet stars have over 20 times the mass of the Sun and are thought to be in a brief, pre-supernova phase of massive star evolution. Fast winds from this Wolf-Rayet star create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of evolution. The windblown nebula has an age of about 70,000 years. Relatively faint emission captured in the expansive image is dominated by the glow of ionized oxygen atoms mapped to bluish hues.