The Antarctic Circle is a parallel of latitude, a cartographic feature based on natural phenomena, situated at 66 degrees and 33 minutes south of the EQUATOR. The circle, as defined on Earth’s surface at the southern end, marks the northern limit of the area in which the Sun does not rise on the summer solstice, on or about June 22, or does not set on the winter solstice, on or about December 22. The period of continuous night or day increases from one day along the Antarctic Circle to six months at the SOUTH POLE. The equivalent cartographic feature at the opposite northern end of Earth is the ARCTIC CIRCLE.
The Antarctic Circle was not crossed until late in the history of exploration, despite numerous expeditions in search of the GREAT SOUTHERN CONTINENT. The first recorded crossing was made by Englishman JAMES COOK on January 17, 1773. The regions within the Antarctic Circle were uninhabited until the 20th century, when outposts for scientific research were built.