Throughout the Universe are vast diffuse clouds of gas and dust called nebulae. If a star lies nearby, a nebula can glow either by reflection of the star’s light or by being molecularly activated --“set on fire”--by the star. The resultant glowing clouds are often extremely beautiful. If the nebula lies in an empty region of space, it appears as an enormous patch of blackness, blotting out the light of stars behind it. Some particularly active nebulae are known to be the birthplace of stars.

Clockwise—Reflection NGC 1999, Vail NGC6995, Star-forming Cluster NGC602, Spirograph IC418, Cat's Eye NGC6543, HST, courtesy NASA