In astronomy, a coma (from the Greek κόμη, "hair") is the nebulous envelope around the nucleus of a comet. It is formed when the comet passes close to the Sun on its highly elliptical orbit; as the comet warms, parts of it sublimate. This gives a comet a "fuzzy" appearance when viewed in telescopes and distinguishes it from stars.

The coma is generally made of ice and dust. Water dominates up to 90% of the volatiles that outflow from the nucleus when the comet is within 3-4 AU of the Sun. The H₂O parent molecule is destroyed primarily through photodissociation and to a much smaller extent photoionization. The solar wind plays a minor role in the destruction of water compared to photochemistry. Larger dust particles are left along the comet's orbital path while smaller particles are pushed away from the Sun into the comet's tail by light pressure.

About a month after an outburst in October 2007, comet 17P/Holmes briefly had a tenuous dust atmosphere larger than the Sun. The Great Comet of 1811 also had a coma roughly the diameter of the Sun. Even though the coma can become quite large, its size can actually decrease about the time it crosses the orbit of Mars around 1.5 AU from the Sun. At this distance the solar wind becomes strong enough to blow the gas and dust away from the coma, enlarging the tail.

In medicine, a coma (from the Greek κῶμα koma, meaning deep sleep) is a state of unconsciousness, lasting more than six hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light, sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions. A person in a state of coma is described as comatose. Although, according to the Glasgow Coma Scale, a person with confusion is considered to be in the mildest coma.

Selena Marie Gomez (born July 22, 1992) is an American actress and singer best known for portraying Alex Russo in the Emmy Award-winning Disney Channel television series Wizards of Waverly Place. She subsequently ventured into feature films and has starred in the television movies Another Cinderella Story, Wizards of Waverly Place: The Movie, and Princess Protection Program. She made her starring theatrical film debut in Ramona and Beezus.

Her career has expanded into the music industry; Gomez is the lead singer and founder of the pop band Selena Gomez & the Scene, which has released three RIAA Gold certified studio albums, Kiss & Tell, A Year Without Rain, and When the Sun Goes Down, spawned three RIAA Platinum certified singles, "Naturally", "Who Says" and "Love You Like a Love Song" and charted four No. 1 Billboard Hot Dance Club Songs. Gomez has also contributed to the soundtracks of Tinker Bell, Another Cinderella Story, Wizards of Waverly Place, and Shake It Up after signing a record deal with Hollywood Records.