The Antarctic Circle is the southernmost of the five principal circles of latitude that cartographers use to divide the Earth. It lies at approximately 66°33′ south of the Equator and is the parallel of latitude that separates the high southern latitudes from the rest of the globe. As one of the major circles of latitude, it appears on many thematic and navigational maps and helps define climatic zones and astronomical phenomena for the southern polar region. The term is often discussed alongside other reference lines used on maps of the Earth.

Key characteristics

Every location south of the Antarctic Circle experiences at least one full day each year when the Sun remains continuously above the horizon, commonly called the midnight sun, and at least one full day when the Sun remains entirely below the horizon, known as the polar night. These extremes result from the tilt of the Earth’s axis: during the southern hemisphere summer the south polar region is tilted toward the Sun, and during winter it is tilted away. The precise latitude of the circle is not fixed over geological time because the tilt of Earth's axis changes slightly, causing the circle to move by small amounts.

Geography and environment

The area south of this parallel is commonly called the Antarctic. Much of this zone is covered by the continent itself; Antarctica is the cold, largely ice-covered continent that dominates the region and gives the zone its name. Surrounding the landmass is the Southern Ocean, which encircles the continent and influences global ocean circulation and climate. At the center of the land mass, and well inside the circle, lies the South Pole, the southernmost point on Earth.

Climate, ecology and notable facts

Antarctica is the coldest, driest and windiest of the continents. Temperatures on the high interior are extreme: the lowest reliably measured surface air temperatures on Earth have been recorded there, roughly around −89 °C (about −128 °F). Despite the harsh conditions, a range of specially adapted life exists along the coasts and on surrounding sea ice, including penguins, seals, and various seabirds. Ice sheets and floating ice shelves play key roles in global sea level and climate dynamics.

Human presence and activity

There is no indigenous permanent population south of the Antarctic Circle. Human activity is concentrated at scientific research bases established by many nations under the terms of the Antarctic Treaty system. Teams of scientists and support staff occupy research stations on a seasonal or year-round basis to study climate, biology, glaciology, astronomy and other fields. Historically, the region also hosted temporary settlements associated with sealing and whaling in the 19th and 20th centuries.

History, navigation and distinctions

The Antarctic Circle has been a useful concept for navigators, explorers and scientists since the age of polar exploration. It is one of several latitudinal markers—alongside the Tropics and the parallel of latitude at the Equator—used to describe solar motion and climate zones. Cartographers and educators often reference the circle when explaining seasonal daylight variation and polar phenomena. The region inside the circle is sometimes simply called the Antarctic and is distinguished from the Southern Temperate Zone to its north.

Further reading and resources