Antarctic Circle in the context of "Middle latitudes"

South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern subregion of the Americas.

South America is bordered on the west by the Pacific Ocean, on the north and east by the Atlantic Ocean, and to the south by the Drake Passage; North America, the Caribbean Sea lying to the northwest, and the Antarctic Circle, Antarctica, and the Antarctic Peninsula to the south.

Antarctica (/ænˈtɑːrktɪkə/ ) is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. Antarctica is the fifth-largest continent, being about 40% larger than Europe, and has an area of 14,200,000 km (5,500,000 sq mi). Most of Antarctica is covered by the Antarctic ice sheet, with an average thickness of 1.9 km (1.2 mi).

Antarctica is, on average, the coldest, driest, and windiest of the continents, and has the highest average elevation. It is mainly a polar desert, with annual precipitation of over 200 mm (8 in) along the coast and far less inland. About 70% of the world's freshwater reserves are frozen in Antarctica, which, if melted, would raise global sea levels by almost 60 metres (200 ft). Antarctica holds the record for the lowest measured temperature on Earth, −89.2 °C (−128.6 °F). The coastal regions can reach temperatures over 10 °C (50 °F) in the summer. Native species of animals include mites, nematodes, penguins, seals and tardigrades. Where vegetation occurs, it is mostly in the form of lichen or moss.

Ascension Island is an isolated volcanic island, 7°56′ south of the Equator in the South Atlantic Ocean. It is about 960 miles (1,540 km) from the coast of Africa and 1,400 miles (2,300 km) from the coast of South America. It is governed as part of the British Overseas Territory of Saint Helena, Ascension and Tristan da Cunha, of which the main island, Saint Helena, is around 800 miles (1,300 km) to the southeast. The territory also includes the sparsely populated Tristan da Cunha archipelago, 2,000 miles (3,200 km) to the south, about halfway to the Antarctic Circle.

Ascension Island was possibly discovered by the Portuguese seafarer João da Nova in 1501, before being named Ascension by Afonso de Albuquerque in 1503 on Ascension Day. Ascension Island was garrisoned by the British Admiralty from 22 October 1815 to 1922 and was an important refuelling stop for ships and commercial airliners in the days of international air travel by flying boats. During World War II, it was an important naval and air station, especially providing antisubmarine warfare bases in the Battle of the Atlantic.

The Arctic Circle is one of the two polar circles, and the northernmost of the five major circles of latitude as shown on maps of Earth at about 66° 34' N. Its southern counterpart is the Antarctic Circle.

The Arctic Circle marks the southernmost latitude for which at the December solstice (winter) the Sun does not rise and at the June solstice (summer) the Sun does not set. These phenomena are referred to as polar night and midnight sun, respectively, and the closer to the pole one goes, the longer that situation persists. For example, in the Russian port city of Murmansk (three degrees north of the Arctic Circle) the Sun stays below the horizon for 20 days before and after the winter solstice, and above the horizon for 20 days before and after the summer solstice.

Bouvet Island (/ˈbuːveɪ/ BOO-vay; Norwegian: Bouvetøya [bʉˈvèːœʏɑ]) is an uninhabited subantarctic volcanic island and dependency of Norway. A protected nature reserve situated in the South Atlantic Ocean at the southern end of the Mid-Atlantic Ridge, it is the world's most remote island. Located north of the Antarctic Circle, Bouvet Island is not part of the southern region covered by the Antarctic Treaty System.

The island lies 1,700 km (1,100 mi; 920 nmi) north of the Princess Astrid Coast of Queen Maud Land, Antarctica, 1,870 km (1,160 mi; 1,010 nmi) east of the South Sandwich Islands, 1,845 km (1,146 mi; 996 nmi) south of Gough Island, and 2,520 km (1,570 mi; 1,360 nmi) south-southwest of the coast of South Africa. It has an area of 49 km (19 sq mi), 93 percent of which is covered by a glacier. The centre of the island is the ice-filled crater of an inactive volcano. Some skerries and one smaller island, Larsøya, lie along its coast. Nyrøysa, created by a rockslide in the late 1950s, is the only easy place to land and is the location of a weather station.

The five main latitude regions of Earth's surface comprise geographical zones, divided by the major circles of latitude. The differences between them relate to climate. They are as follows:

1. The North Frigid Zone, between the North Pole at 90° N and the Arctic Circle at 66°33′50.7″ N, covers 4.12% of Earth's surface.
2. The North Temperate Zone, between the Arctic Circle at 66°33′50.7″ N and the Tropic of Cancer at 23°26′09.3″ N, covers 25.99% of Earth's surface.
3. The Torrid Zone, between the Tropic of Cancer at 23°26′09.3″ N and the Tropic of Capricorn at 23°26′09.3″ S, covers 39.78% of Earth's surface.
4. The South Temperate Zone, between the Tropic of Capricorn at 23°26′09.3″ S and the Antarctic Circle at 66°33′50.7″ S, covers 25.99% of Earth's surface.
5. The South Frigid Zone, from the Antarctic Circle at 66°33′50.7″ S and the South Pole at 90° S, covers 4.12% of Earth's surface.

On the basis of latitudinal extent, the globe is divided into three broad heat zones.

The Antarctic (/ænˈtɑːr(k)tɪk/, US also /æntˈɑːr(k)tɪk/; commonly /ænˈɑːrtɪk/) is the polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is diametrically opposite of the Arctic region around the North Pole.

The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau, and other island territories located on the Antarctic Plate or south of the Antarctic Convergence. The Antarctic region includes the ice shelves, waters, and all the island territories in the Southern Ocean situated south of the Antarctic Convergence, a zone approximately 32 to 48 km (20 to 30 mi) wide and varying in latitude seasonally. The region covers some 20 percent of the Southern Hemisphere, of which 5.5 percent (14 million km) is the surface area of the Antarctica continent itself. All of the land and ice shelves south of 60°S latitude are administered under the Antarctic Treaty System.

A polar circle is a geographic term for a conditional circular line (arc) referring either to the Arctic Circle or the Antarctic Circle. These are two of the keynote circles of latitude (parallels). On Earth, the Arctic Circle is currently drifting northwards at a speed of about 14.5 m per year and is now at a mean latitude (i.e. without taking into account the astronomical nutation) of 66°33′50.7″ N; the Antarctic Circle is currently drifting southwards at a speed of about 14.5 m per year and is now at a mean latitude of 66°33′50.7″ S. Polar circles are often equated with polar regions of Earth. Due to their inherent climate environment, the bulk of the Arctic Circle, much of which is sea, is sparsely settled whereas this applies to all of Antarctica which is mainly land and sheltered ice shelves.

If Earth had no atmosphere, then both polar circles (arcs) would see at least a day a year when the center of the Sun is continuously above the horizon and at least a day a year when it is always below the horizon – a polar day and a polar night as is the case for longer, within the circles. Up to and including the associated poles (North and South), known geographically as the frigid zones, such duration extends up to half of the year, namely, close to the poles. Instead, atmospheric refraction and the Sun's light reaching the planet as an extended object rather than a point source means that just within each circle the Earth's surface does not experience any proper polar night, 24 hours where the sun does not rise. By these same two factors, just outward of each circle still experiences a polar day (a day in which the sun does not fully set).