Nebulae

Clouds of interstellar gas and dust, classified by what lights or shapes them: star-forming and emission nebulae glow from young stars within them, planetary nebulae and supernova remnants are the expelled outer layers of a dying star, and dark and reflection nebulae are seen by the light they block or scatter rather than emit. Belongs here: any entry whose defining nature is a cloud of gas or dust rather than a discrete body. Does not belong here: the star or stellar remnant that may sit at a nebulas center, grouped under Stars or Black Holes and Compact Objects.