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"
Dusty Nebulae in Taurus
11/07/2013
This complex of dusty nebulae linger along the edge of the Taurus molecular cloud, a mere 450 light-years distant. Stars are forming on the cosmic scene, including extremely youthful star RY Tauri prominent toward the upper left of the 1.5 degree wide telescopic field. In fact RY Tauri is a pre-main sequence star, embedded in its natal cloud of gas and dust, also cataloged as reflection nebula vdB 27. Highly variable, the star is still relatively cool and in the late phases of gravitational collapse. It will soon become a stable, low mass, main sequence star, a stage of stellar evolution achieved by our Sun some 4.5 billion years ago. Another pre-main sequence star, V1023 Tauri, can be spotted below and right, embedded in its yellowish dust cloud adjacent to the striking blue reflection nebula Ced 30.