Arctic Circle

The Arctic Circle is one of the two polar circles, and the northernmost of the five major circles of latitude. It is shown on maps of Earth at about 66° 34' N. Its southern counterpart is the Antarctic Circle. The Arctic Circle marks the southernmost latitude for which at the December solstice (winter) the Sun does not rise and at the June solstice (summer) the Sun does not set. These phenomena are referred to as polar night and midnight sun, respectively, and the closer to the pole one goes, the longer that situation persists. For example, in the Russian port city of Murmansk (three degrees north of the Arctic Circle) the Sun stays below the horizon for 20 days before and after the winter solstice, and above the horizon for 20 days before and after the summer solstice. The positions of the Arctic and Antarctic Circles vary slightly from year to year. Currently the Arctic Circle is 66°33′51.1″ north of the Equator. Its latitude depends on Earth's axial tilt, which fluctuates by a margin of some 2° over a 41,000-year period due to tidal forces resulting from the orbit of the Moon. Consequently, in the current epoch the Arctic Circle is drifting toward the North Pole, while the Antarctic Circle drifts towards the South Pole, each at a speed of about 14.5 m (48 ft) per year.