Arctic Circle
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World map showing the Arctic Circle in red |
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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″ (or 66.56083
°) 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 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 arctic
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 in local
vernacular 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.(In fact, because of the
atmospheric 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, however 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 41000 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 15 m per year. Also see
precession.
Countries which have significant territory within the Arctic Circle are:
*
Russia*
Canada*
Denmark (
Greenland)
*
United States (
Alaska)
*
Norway*
Sweden*
FinlandThe country of
Iceland also has territory within the Arctic Circle, but less than 1 km². This area is on a few small islets, of which only
Grímsey (which lies directly on the Arctic Circle) is inhabited.
*
Antarctic Circle*
Circumpolar arctic*
Topographical map of Arctic Circle, centered about North Pole*
Map of Arctic Circle (dotted line), showing major population areas*
Terra Incognita: Exploration of the Canadian Arctic — Historical essay about early expeditions to the Canadian arctic, illustrated with maps, photographs and drawings
