An immense interstellar, diffuse cloud of gas and dust from which a central star and surrounding planets and planetesimals condense and accrete. The properties of nebulae vary enormously and depend on their composition as well as the environment in which they are situated. Emission nebula are powered by young, massive stars and emit their own light, reflection nebulae shine by reflecting light from nearby massive stars, and dark nebulae, as the name suggests, are dark and can only be seen when silhouetted against a bright background.

Some or all content above used with permission from J. H. Wittke.