The Arctic Circle marks a change in daily patterns of sunlight and darkness as one heads north. In the area of the globe between the Arctic Circle and its southern counterpart, the Antarctic Circle (which lies at approximately 66°33’ S), the sun rises and sets daily. North of the Arctic Circle, however, the sun does not set at midsummer (also known as the summer solstice), on 20 or 21 June. Conversely, the sun does not rise at midwinter (also known as the winter solstice), on 21 or 22 December. The midwinter sun can still be seen at places slightly north of the Arctic Circle when it is just below the horizon, since light rays are bent by the Earth’s atmosphere.
Midnight Sun and Polar Night
From one day at the Arctic Circle, the number of continuous days of sunlight or darkness increases northward to a full six months at the North Pole. In summer, this phenomenon is known as the midnight sun, while in the winter it is called polar night.
These effects of continuous light and darkness occur because the Earth’s axis of rotation is tilted relative to the plane of its orbit around the sun. Winter in the Arctic Circle occurs when the Northern Hemisphere is tilted away from the sun during the planet’s annual rotation. At this time, the Earth’s curvature creates an area of permanent shadow or darkness centred on the North Pole. This area starts to form at the fall equinox (22 or 23 September), and grows to a maximum at midwinter. It then decreases, vanishing by the spring equinox (20 or 21 March). For the remainder of the year, when the Northern Hemisphere is tilted toward the sun, an area of permanent sunlight centres on the North Pole.
Geography and Human Habitation
The Arctic Circle does not mark a change in climate. Trees grow north of it in the Mackenzie Delta, where the Mackenzie River meets the Arctic Ocean in the Northwest Territories (see also Delta; Ocean). By comparison, in northern Québec, the treeline is approximately 1,000 km south of the Arctic Circle.
Inuvik, also in the Mackenzie Delta, is the only moderately large Canadian settlement lying north of the circle. It is accessible via the Dempster Highway, which runs north from Dawson, Yukon. Communities in the Canadian North that are located near the Arctic Circle include Old Crow in the Yukon, Fort McPherson in the Northwest Territories, and Repulse Bay and Qikiqtarjuaq in Nunavut.
Challenges North of the Arctic Circle
Climate change is more severe in the Arctic than in most other places on Earth, the region warming almost two times faster than the global average. This presents challenges for inhabitants of the Arctic. In Canada, the Inuit are observing changes in the migration patterns and population numbers of arctic animals. Resource development and industrial activity also threaten animal habitats. Given the importance of animals such as the walrus and seal to the Inuit, these changes in turn threaten their traditions and culture.