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"
M16: Stars Upon Pillars
06/11/1995
How do stars form? This stunning picture taken recently by the Hubble Space Telescope gives us a first hand glimpse. Here evaporating gaseous globules (EGGs) are captured emerging from pillars of molecular hydrogen and dust in the Eagle Nebula (M16). These pillars, dubbed "elephant trunks," are light years in length and are so dense that interior gas gravitationally contracts to form stars. At each pillars' end, the intense radiation of bright young stars causes low density gas to boil away, leaving stellar nurseries of dense EGGs exposed.