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"
Stars Forming in Serpens
31/08/2007
Stars are forming in a dense molecular cloud a mere 1,000 light-years away in the constellation Serpens Cauda (The Serpent's Tail). At that estimated distance, this sharp, near-infrared close-up of the active Serpens star-forming region spans about 2 arcminutes or just over half a light-year. Though such near-infrared observations can be made by mountain-top telescopes with specialized detectors, near-infrared light has too long a wavelength to be visible to the eye. This view was recorded with a sensitive camera, HAWK-I (High Acuity, Wide field K-band Imaging), just commissioned at the Paranal Observatory in Chile. Intended to illustrate HAWK-I's impressive capabilities, the tantalizing image highlights reddish young stars and protostars, likely up to a few million years old, emerging from the nebular gas and dust.