The Arctic Circle is the most northerly of the five major circles of latitude that mark maps of the Earth. The region north of this circle is known as the Arctic, and the zone just to the south is called the Northern Temperate Zone.
North of the Arctic Circle, the sun is above the horizon for twenty-four continuous hours at least once per year (and therefore visible at midnight) and below the horizon for twenty-four continuous hours at least once per year (and therefore not visible at noon); this is also true within the equivalent polar circle in the Southern Hemisphere, the Antarctic Circle.
The position of the Arctic Circle is not fixed; as of 16 December 2016, it runs 66°33′46.5″ north of the Equator. Its latitude depends on the Earth’s axial tilt, which fluctuates within a margin of 2° over a 40,000-year period, due to tidal forces resulting from the orbit of the Moon.Consequently, the Arctic Circle is currently drifting northwards at a speed of about 15 m (49 ft) per year.
The Arctic Circle is the parallel of latitude that runs 66° 33′ 39,” or roughly 66.5°, north of the Equator. Approximately 15,000 kilometers (9,300 miles) to the south is the Antarctic Circle, of equal diameter to and parallel to the Arctic Circle as well as equally distant from the Equator. Together with the Equator and the tropics of Cancer and Capricorn, these five unseen circular lines comprise the major circles of latitude that mark maps of the Earth.
All five are determined by the Earth’s rotation on its axis and the Earth’s tilt toward and away from the Sun in its orbit. The circle, though invisible and, in fact, moving, is a product of the same phenomenon that provides the world with four seasons and this largely austere part of the globe with an odd formula of light and darkness shared only by its polar opposite.
The Arctic Ocean lies wholly within the Arctic Circle. The ocean, the circle, and the region take their names from the Greek word arctus, meaning “bear,” a reference to the Big and Little Bear constellations that can always be seen overhead on clear nights in the polar region.
Everything north of the Arctic Circle is properly known as the Arctic while the zone just to the south of the circle is the Northern Temperate Zone. The North Pole lies about 2,600 kilometers (1,600 miles) from the Arctic Circle. Because of the moderating influence of open water—even warm water escaping from under polar pack ice— the North Pole is often less cold than points on the circle.