Antarctic Circle

Antarctic Circle

Antarctic Circle, imaginary circle on the surface of the earth at 661/2°S lat., i.e., 231/2° north of the South Pole. It marks the southernmost point at which the sun can be seen at the winter solstice (about June 22) and the northernmost point of the southern polar regions at which the midnight sun is visible.

Parallel of latitude approximately 66°30' south of the Equator that circumscribes the southern frigid zone. It marks the northern limit of the area within which, for one day or more each year, the sun does not set or rise. The length of continuous day or night increases southward from the Antarctic Circle, mounting to six months at the South Pole.

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The Antarctic Circle is one of the five major circles (or parallels) of latitude that mark maps of the Earth. As of 2000, it lies at latitude 66° 33′ 39″ (or 66.56083°) south of the equator. The area south of the Antarctic Circle is known as the Antarctic, and the zone immediately to the north is called the Southern Temperate Zone. The equivalent line of latitude in the northern hemisphere is the Arctic Circle.

Every place south of the Antarctic Circle experiences a period of twenty-four hours' continuous daylight at least once per year, and a period of twenty-four hours' continuous night time at least once per year. That is to say, there is at least one whole day during which the sun does not set, and at least one whole day during which the sun does not rise. On the Antarctic Circle these events occur, in principle, exactly once per year, at the December solstice and June solstice respectively. This happens because the earth's axis is tilted, by approximately 23.5 degrees, relative to ecliptic (the plane of the earth's orbit around the sun). At the June solstice the southern hemisphere is tilted away from the Sun to its maximum extent, and the region of permanent darkness reaches its northern limit; at the December solstice the southern hemisphere is tilted towards the Sun to its maximum extent, and the region of permanent sunlight reaches its northern limit.

In practice several other factors affect the appearance of continuous day or night, the most important being atmospheric refraction, the altitude of the observer above sea level, mirages, and the fact that the sun is a disc rather than a point. Mirages on the Antarctic continent tend to be even more spectacular than in Arctic regions, creating, for example, a series of apparent sunsets and sunrises while in reality the sun remains under the horizon.

Due to gradual changes in the tilt of the Earth's axis, the Antarctic Circle is slowly moving..

Geography and demographics

The continent of Antarctica forms a land mass covering much of the area within the Antarctic Circle. There is no permanent human population on Earth south of the Antarctic Circle. There are, however, several Antarctic research centers from various nations that are inhabited by teams of scientists that rotate on a seasonal basis. In previous centuries, some semi-permanent whaling stations were established on the continent and some of the whalers would live there for a year or more. At least three children have been born in Antarctica. However, they were born in stations north of the Antarctic Circle.

Starting at the Prime Meridian and heading eastwards, the Arctic Circle passes through:

long Territory or sea Notes
Southern Ocean north of Queen Maud Land
30° E Southern Ocean north of Queen Maud Land
60° Southern Ocean north of Queen Maud Land, Amery Ice Shelf
90° Wilkes Land
120° Wilkes Land
150° E Southern Ocean north of Victoria Land
180° Southern Ocean Ross Sea
150° W Southern Ocean north of Marie Byrd Land
120° Southern Ocean Amundsen Sea
90° Southern Ocean Peter Island
60° Graham Land
30° W Weddell Sea

See also

References

External links

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