Sunspot

Sunspot, apparent dark spot on the surface of the sun. Vortices of gas associated with strong electromagnetic activity, sunspots appear dark only by contrast with the surrounding photosphere. Single spots are known, but mostly they form in groups or pairs. They are never seen at the sun's poles or equator. Their cause is not known, but they seem cyclical, reaching a maximum about every 11 years.

See also: Sun.