In the Northern Hemisphere is the Arctic Circle, and in the Southern, respectively, - the line of the Southern Arctic Belt. The first is considered the boundary of the temperate zone and the Arctic. The Antarctic Circle is considered the climatic boundary of Antarctica. On June 21-22 (summer solstice) the sun does not set, and on winter solstice (December 21-22) it does not rise.
Due to changes in the tilt of the earth's axis, there is a daily shift of the line of the Arctic circle (Arctic circle) up to three meters per day and up to one hundred meters per year. Experts made calculations up to 2015. It is established that at first the Arctic Circle will shift to the north. In the next nine years after 2015, four hundred meters south.
The boundary of the polar night is determined by the polar circle, if the Sun is a luminous point, while the Earth does not have an atmosphere. In fact, the day begins when the top point of the solar disk appears. Moreover, the apparent position of the luminary is higher than the real one due to refraction (bending of the rays in the atmosphere). In this regard, the Arctic Circle lies fifty minutes south of the polar night limit.
For the first time the concept of the Arctic circle was introduced by Eudoxus of Cnidus(a student of Plato). He understood the relationship between the tilt of the planet's axis and illumination in different areas of the Earth, connected the climate and latitude of the area. Eudoxus introduced the definition of "climate". The location of the Arctic Circle, in his opinion, was at 54 degrees. All places behind him were considered unsuitable for human life.
About 327 B. C. The first navigator who was able to cross the Arctic Circle was the geographer Pytheas. He observed the Arctic day in the Norwegian Sea.
The first navigator to cross the Southern Circle was Cook. It happened during his trip around the world.
The Arctic Circle in Europe runs through Norway, Finland, Russia, Sweden. The line crosses in Russia the Republic of Karelia, the Murmansk region, the Kandalaksha Bay and the Mezen Bay in the White Sea, the Nenets Autonomous Okrug, Komi and other regions. The part of the mainland, which is located north of the circle, is called the Arctic.
Across the Bering Strait, the line continues to America. In this territory, the Arctic Circle passes through Alaska, three regions of Canada. Further, the line goes along Baffin Island, Fox Bay, Greenland and Davis Strait.
The Northern Circle in the North Atlantic passes through the Danish Strait, Grimsey Island belonging to Iceland, as well as the Norwegian and Greenland Seas.
The southern circle crosses a number of territories of Antarctica and the Southern Ocean. The line passes through the Antarctic Peninsula, the Lazarev Sea, Weddell Sea, Cosmonauts Sea, Amundsen Bay and the Riiser-Lansen Sea. From the shore of the Amundsen Bay lineThe Arctic Circle crosses the Commonwe alth Sea, Enderby and Princess Elizabeth Land, Truth Coast, Davis Sea, Vincennes Bay in the Mawson Sea, and Knox Coast. Further, the line alternately passes over the ocean and along various coasts on Wilkes land. Not far from "Dumont-Durville" (French station) it enters the Pacific sector in the Southern Ocean from the Antarctic continent.
