Circle of latitude
From Wikipedia, the free encyclopedia
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| Map of Earth | |
| Longitude (λ) | |
|---|---|
| Appear curved and vertical in this projection, but are actually halves of great circles. | |
| Latitude (φ) | |
| Appear straight and horizontal in this projection, but are actually circular with different radii. All locations with a given latitude are collectively referred to as a circle of latitude. | |
| The equator divides the planet into a Northern Hemisphere and a Southern Hemisphere, and has a latitude of 0°. |  |
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):
- the Arctic Circle (66° 33′ 38″ N)
- the Tropic of Cancer (23° 26′ 22″ N)
- the Equator (0° N)
- the Tropic of Capricorn (Sagittarius) (23° 26′ 22″ S)
- the Antarctic Circle (66° 33′ 38″ S)
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[edit] Major latitudes
[edit] 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.
[edit] 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°.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] Notable parallels
| Parallel | Description |
|---|---|
| 49th parallel north | Part of the border between the United States and Canada, from Washington to western Minnesota. |
| 45th parallel north | The border between Vermont and Quebec. |
| 42nd parallel north | The border between California and Oregon. |
| 41st parallel north | Parts of the borders of Colorado, Utah, Wyoming, and Nebraska. |
| 40th parallel north | The line originally chosen for the Mason-Dixon Line, but the line was moved several miles south to avoid bisecting the city of Philadelphia. |
| 39° 43′ 19.92216″ N | Mason-Dixon line |
| 38th parallel north | Boundary between the Soviet and American occupation zones in Korea in 1945. |
| 37th parallel north | North-south border between Utah & Arizona, and Colorado & New Mexico respectively. |
| 33rd parallel north | The border between Louisiana and Arkansas |
| 28th parallel north | Boundary between Baja California and Baja California Sur in Mexico. |
| 22° 19' 35.6736" N | Boundary Street - Boundary between Kowloon and New Kowloon of New Territories |
| 17th parallel north | Division between Republic of Vietnam (South Vietnam) and Democratic Republic of Vietnam (North Vietnam) during the Vietnam war. |
| 45th parallel south | The 45th parallel of south latitude is the east-west line that marks the theoretical halfway point between the equator and the South Pole. |
| 60th parallel south | Area south of which is considered Antarctica for the purposes of the Antarctic Treaty System (see map) |
