Arctic Circle

Map of the Arctic, with the Arctic Circle in blue and the 10°C July  mean isotherm in red

The Arctic Circle is one of the two polar circles and the most northerly of the five major circles of latitude as shown on maps of Earth. It marks the northernmost point at which the center of the noon sun is just visible on the December solstice and the southernmost point at which the center of the midnight sun is just visible on the June solstice. The region north of this circle is known as the Arctic, and the zone just to the south is called the Northern Temperate Zone.

As seen from the Arctic, the Sun is above the horizon for 24 continuous hours at least once per year (and therefore visible at midnight) and below the horizon for 24 continuous hours at least once per year (and therefore not visible at noon). This is also true in the Antarctic region, south of the equivalent Antarctic Circle.

The position of the Arctic Circle is not fixed and currently runs 66°33′48.5″ north of the Equator. Its latitude depends on the Earth's axial tilt, which fluctuates within a margin of more than 2° over a 41,000-year period, due to tidal forces resulting from the orbit of the Moon. Consequently, the Arctic Circle is currently drifting northwards (shrinking) at a speed of about 15 m (49 ft) per year.

Etymology

The word arctic comes from the Greek word ἀρκτικός (arktikos: "near the Bear, northern") and that from the word ἄρκτος (arktos: "bear").

Midnight sun and polar night

Relationship of Earth's axial tilt (ε) to the tropical and polar circles
At night, bright aurora borealis are a fairly common sight in the Arctic Circle. The picture of the northern lights in Rovaniemi.

The Arctic Circle is the southernmost latitude in the Northern Hemisphere at which the center of the sun can remain continuously above or below the horizon for twenty-four hours; as a result, at least once each year at any location within the Arctic Circle the center of the sun is visible at local midnight, and at least once the center is not visible at local noon.

Directly on the Arctic Circle these events occur, in principle, exactly once per year: at the June and December solstices, respectively. However, because of atmospheric refraction and mirages, and also because the sun appears as a disk and not a point, part of the midnight sun may be seen on the night of the northern summer solstice up to about 50 minutes (′) (90 km (56 mi)) south of the Arctic Circle; similarly, on the day of the northern winter solstice, part of the sun may be seen up to about 50′ north of the Arctic Circle. That is true at sea level; those limits increase with elevation above sea level, although in mountainous regions there is often no direct view of the true horizon.

Human habitation

Cylindrical projection showing the Arctic Circle in red

Only four million people live north of the Arctic Circle due to the climate; nonetheless, some areas have been settled for thousands of years by indigenous peoples, who today make up 10% of the region's population. The largest communities north of the Arctic Circle are situated in Russia, Norway and Sweden: Murmansk (population 295,374), Norilsk (178,018), Tromsø (75,638), Vorkuta (58,133), and Kiruna (22,841). Rovaniemi (62,667) in Finland is the largest settlement in the immediate vicinity of the Arctic Circle, lying 6 km (4 mi) south of the line.

In contrast, the largest North American community north of the Arctic Circle, Sisimiut (Greenland), has approximately 5,000 inhabitants. In the United States, Utqiagvik, Alaska is the largest settlement north of the Arctic Circle with about 4,000 inhabitants. The largest such community in Canada is Inuvik in the Northwest Territories, with 3,200 people living there.

Geography

The Arctic Circle is roughly 16,000 km (9,900 mi) long. The area north of the Circle is about 20,000,000 km2 (7,700,000 sq mi) and covers roughly 4% of Earth's surface.

The Arctic Circle passes through the Arctic Ocean, the Scandinavian Peninsula, North Asia, Northern America, and Greenland. The land within the Arctic Circle is divided among eight countries: Norway, Sweden, Finland, Russia, the United States (Alaska), Canada (Yukon, Northwest Territories, and Nunavut), Denmark (Greenland), and Iceland (where it passes through the small offshore island of Grímsey).

Climate

The climate inside the Arctic Circle is generally cold, but the coastal areas of Norway have a generally mild climate as a result of the Gulf Stream, which makes the ports of northern Norway and northwest Russia ice-free all year long. In the interior, summers can be quite warm, while winters are extremely cold. For example, summer temperatures in Norilsk, Russia will sometimes reach as high as 30 °C (86 °F), while the winter temperatures frequently fall below −50 °C (−58 °F).

Sites along the Arctic Circle

Starting at the prime meridian and heading eastwards, the Arctic Circle passes through:

A sign along the Dalton Highway marking the location of the Arctic Circle in Alaska
Arctic Circle line in Rovaniemi, Finland c.1865

See also

External links

Uses material from the Wikipedia article Arctic Circle, released under the CC BY-SA 3.0 license.