Circle of latitude

A circle of latitude is an imaginary circle around the Earth made up of all the points that have the same particular value for their latitude. These are based on the rotation of the Earth in relationship to the Sun.

The five major circles of latitude are:

• the Arctic Circle (66.5° N)
• the Tropic of Cancer (23.5° N)
• the Equator (0° N)
• the Tropic of Capricorn (23.5° S)
• the Antarctic Circle (66.5° S)

The equator is the most prominent of these circles in that it is also a great circle. The other lines of latitude are not the shortest distance between points (it is for this reason that an aeroplane travelling between a European and North American city on the same lattitude will fly further north, over Greenland for example), and are thus not really "lines" in the geometry of the sphere.

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.

Circles of latitude are often used as boundaries between countries or regions. Notable parallels include:

• 49th parallel north: part of the border between the United States and Canada.
• 45th parallel north: the border between Vermont and Canada.
• 42nd parallel north: the border between California and Oregon.
• 41st parallel north: parts of the borders of Colorado, Utah, Wyoming, and Nebraska.
• 38th parallel north: boundary between the Soviet and American occupation zones in Korea in 1945.