This is a geographic line located at 66° 33' South latitude, marking the southernmost point at which the sun can stay above or below the horizon for 24 hours. It is the southernmost boundary of the polar day (24-hour sunlit day) and the polar night (24
The Antarctic Circle is the most southerly of the five major circles of latitude that mark maps of Earth. The region south of this circle is known as the Antarctic, and the zone immediately to the north is called the Southern Temperate Zone. South of the Antarctic Circle, the Sun is above the horizon for 24 continuous hours at least once per year and the centre of the Sun is below the horizon for 24 continuous hours at least once per year ; this is also true within the Arctic Circle, the Antarctic Circle’s counterpart in the Northern Hemisphere.