Difference between revisions of "Arctic Circle" - New World Encyclopedia

Revision as of 00:42, 17 April 2006

World map showing the five major circles of latitude

A sign along the Dalton Highway marking the location of the Arctic Circle

The Arctic Circle is the parallel of latitude that runs 66° 33' 39", or roughly 66.5°, north of the Equator. Approximately 15,000 km to the south is the Antarctic Circle, of equal diameter and parallel to the Arctic Circle as well as equally distant from the Equator. Together with the tropics of Cancer and Capricorn, these three invisible circular lines comprise the five 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. 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 Arctic Circle marks the southern extremity of the polar day of the summer solstice in June and the polar night of the winter solstice in December. Within the whole area of the Arctic Circle, the Sun is above the horizon for at least 24 continuous hours once per year, in conjunction with the Arctic's summer solstice, which is often referred to as "midnight sun." Likewise, in conjunction with the Arctic's winter solstice, the Arctic sun will be below the horizon in the entire area for at least 24 continuous hours, which could just as easily be known as "noontime darkness." Points within the circle experience longer periods of continuous light and darkness depending on their proximity to the North Pole, where six months of sunlight alternate with a half-year of darkness.

(In fact, because of refraction and because the sun appears as a disk and not a point, part of the midnight sun may be seen at the night of the summer solstice up to about 50' (90 km) south of the geometric arctic circle; similarly, at the day of the winter solstice part of the sun may be seen up to about 50' north of the geometric arctic circle. This is true at sea level; these limits increase with elevation above sea level, but in mountainous regions there is often no direct view of the horizon.)

The position of the Arctic Circle is determined by the axial tilt (angle) of the polar axis of rotation of the Earth on the ecliptic. This angle is not constant, but has a complex motion determined by many cycles of short to very long periods. Due to nutation the tilt oscillates over 9" (about 280 m on the surface) over a period of 18.6 years. The main long-term cycle has a period of 41,000 years and an amplitude of about 0.68°, or 76 km on the surface. Currently the tilt is decreasing by about 0.47" per year, so the Arctic Circle is moving north by about 14 meters per year. Also see precession.

Countries that have significant territory within the Arctic Circle are:

Russia
Canada
Greenland
United States (Alaska)
Norway
Sweden
Finland

The country of Iceland also has territory within the Arctic Circle, but less than 1 sq km. This area is on a few small islets, of which only Grímsey (which lies directly on the Arctic Circle) is inhabited.

INFRASTRUCTURE TRANSPORTATION LINKS GLOBAL WARMING NOONTIME NIGHT POLAR ROUTES AGRICULTURE/GROWING SEASON FISHING LIVESTOCK COMMUNICATION LINKS

External links

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 [[Image:Arctic Circle sign.jpg|thumb|right|200px|A sign along the [[Dalton Highway]] marking the location of the Arctic Circle]]
-The '''Arctic Circle''' is one of the five major circles of latitude that mark maps of the [[Earth]]. This is the parallel of [[latitude]] that (in 2000) runs 66° 33' 39" north of the [[Equator]]. Everything north of this circle is known as the [[Arctic]], and the zone just to the south of this circle is the [[Northern Temperate Zone]].
+The '''Arctic Circle''' is the parallel of latitude that runs 66° 33' 39", or roughly 66.5°, north of the [[Equator]]. Approximately 15,000 km to the south is the Antarctic Circle, of equal diameter and parallel to the Arctic Circle as well as equally distant from the Equator. Together with the tropics of [[Tropic of Cancer|Cancer]] and [[Tropic of Capricorn|Capricorn]], these three invisible circular lines comprise the five 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. 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 Arctic Circle marks the southern extremity of the polar day of the summer solstice in June and the polar night of the winter solstice in December. Within the Arctic Circle, the Sun is above the horizon for at least 24 continuous hours once per year, in conjunction with the Arctic's summer solstice - this is often referred to as [[midnight sun]]. Likewise, in conjunction with the Arctic's Winter Solstice, the Arctic sun will be below the horizon for at least 24 continuous hours.
+The Arctic Circle marks the southern extremity of the polar day of the summer solstice in June and the polar night of the winter solstice in December. Within the whole area of the Arctic Circle, the Sun is above the horizon for at least 24 continuous hours once per year, in conjunction with the Arctic's summer solstice, which is often referred to as "midnight sun." Likewise, in conjunction with the Arctic's winter solstice, the Arctic sun will be below the horizon in the entire area for at least 24 continuous hours, which could just as easily be known as "noontime darkness." Points within the circle experience longer periods of continuous light and darkness depending on their proximity to the [[North Pole]], where six months of sunlight alternate with a half-year of darkness.
 (In fact, because of [[refraction]] and because the sun appears as a disk and not a point, part of the midnight sun may be seen at the night of the summer solstice up to about 50' (90 km) south of the geometric arctic circle; similarly, at the day of the winter solstice part of the sun may be seen up to about 50' north of the geometric arctic circle. This is true at sea level; these limits increase with elevation above sea level, but in mountainous regions there is often no direct view of the horizon.)