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On the Earth, a circle of latitude or parallel is an imaginary east-west circle that connects all locations with a given latitude. The position on the circle of latitude is given by the longitude. Each is perpendicular to all meridians at the intersection points. Those parallels closer to the poles are smaller than those at or near the Equator. For a low latitude a circle of latitude can be said to be a line around the Earth, while at a high latitude it is a circle around a pole. Circles of latitude are often used as boundaries between countries or regions. The five major circles of latitude are (order corresponding to order on map at right from North Pole to South Pole):
Major latitudes Equator The equator is the circle that is equidistant from both the North Pole and South Pole. It splits the Earth into the Northern Hemisphere and the Southern Hemisphere. Image:World map with equator.jpg|Equator Arctic and Antarctic Circles The Arctic Circle represents the southernmost location in the Northern Hemisphere where it is possible to have a day without a sunrise (see midnight sun). Respectively, the Antarctic Circle represents the northernmost location in the Southern Hemisphere where it is possible to have a day without a sunrise. Note that the latitude plus the axial tilt is equal to 90°. Image:World map with arctic circle.jpg|Arctic Circle Image:World map with antarctic circle.jpg|Antarctic Circle Tropic of Cancer and Capricorn The Tropic of Cancer and Tropic of Capricorn represent the northernmost and southernmost locations where the sun may be seen directly overhead (midsummer and midwinter respectively). Note that the latitude of is equal to the axial tilt. Image:World map with tropic of cancer.jpg|Tropic of Cancer Image:World map with tropic of capricorn.jpg|Tropic of Capricorn Not great circles The circles of latitude are loxodromes, but, apart from the equator, they are not great circles, hence not the shortest distance between points, as opposed to what is suggested by maps that show them as straight lines. It is for this reason that an airplane travelling between a European and North American city on the same latitude will fly further north, over Greenland for example. Thus they are not really "lines" in the geometry of the sphere. See also great-circle distance. Parallel A circle of latitude is often called a parallel, because circles of latitude are a fixed distance apart and on some map projections, including the Mercator projection, they are parallel. Also, they are the intersections of the surface of the Earth with parallel planes. Notable parallels | ||||||||
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