Comets are a class of small celestial objects orbiting the Sun and developing diffuse gaseous envelopes and often long luminous tails when near the Sun. The comet makes a transient appearance in the sky and is often said to have a “hairy” tail. The word comes from the Greek komētēs, meaning “hairy one,” a description that fits the bright comets noticed by the ancients. This is an alphabetically ordered list of significant comets. (See also asteroid; Centaur object; Earth impact hazard; Kuiper belt; meteor and meteoroid; small body.)