The circles are imaginary lines that surround the north and south poles at 66.5 degrees latitude. The Arctic Circle is a line of latitude at 66.5 degrees north of the equator and the Antarctic Circle is a line of latitude at 66.5 degrees south. Areas north of the Arctic Circle are dark for 24 hours near December 21 and areas south of the Antarctic Circle are dark for 24 hours near June 21. Almost all of the continent of Antarctica is located to the south of the Antarctic Circle.