Arctic Circle, COD22, in geography, an imaginary line running parallel to the Equator and circling the earth at about 66° 33' north latitude. The Arctic Ocean and the northern fringes of Asia, Europe, and North America lie within the Arctic Circle.

Along the Arctic Circle there is one day each year during which the sun does not set, about June 21 (the Northern Hemisphere's summer solstice, the first day of summer). Similarly, the sun does not rise above the horizon on approximately December 22 (the winter solstice). The number of such days increases toward the North Pole. At the Pole there are six months of continuous daylight (about March 21 to September 23) and six months of darkness (September 23 to March 21).