Antarctic Circle, an imaginary line running parallel to the Equator and circling the earth at about 66° 33' South latitude. Except for a few coastal areas, the continent of Antarctica lies within the circle. .)

Along the Antarctic Circle there is one day each year during which the sun does not set, about December 22 (the summer solstice [first day of summer] in the Southern Hemisphere). Similarly, the sun does not rise above the horizon on approximately June 21 (the winter solstice). The number of days without sunset or sunrise increases with nearness to the South Pole. At the Pole there are six months of continuous darkness (about March 21 to September 23) followed by six months of daylight (September 23 to March 21).