A prime meridian is a meridian in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian form a great circle. This great circle divides a spheroid, e.g., Earth, into two hemispheres. If one uses directions of East and West from a defined prime meridian, then they can be called the Eastern Hemisphere and the Western Hemisphere.
A prime meridian, based at the Royal Observatory, Greenwich, in London, England, was established by Sir George Airy in 1851. By 1884, over two-thirds of all ships and tonnage used it as the reference meridian on their charts and maps. In October of that year, at the behest of US President Chester A. Arthur, 41 delegates from 25 nations met in Washington, D.C., United States, for the International Meridian Conference. This conference selected the meridian passing through Greenwich as the official prime meridian due to its popularity. However, France abstained from the vote, and French maps continued to use the Paris meridian for several decades. In the 18th century, London lexicographer Malachy Postlethwayt published his African maps showing the "Meridian of London" intersecting the Equator a few degrees west of the later meridian and Accra, Ghana.
A (geographical) meridian is the half of an imaginary great circle on the Earth's surface, terminated by the North Pole and the South Pole, connecting points of equal longitude, as measured in angular degrees east or west of the Prime Meridian. The position of a point along the meridian is given by that longitude and its latitude, measured in angular degrees north or south of the Equator. Each meridian is perpendicular to all circles of latitude. Each is also the same length, being half of a great circle on the Earth's surface and therefore measuring 20,003.93 km.
The meridian 110° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole.
The meridian 50° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Europe, Asia, Africa, the Indian Ocean, Madagascar, the Southern Ocean, and Antarctica to the South Pole.
The meridian 60° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Europe, Asia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole.
The meridian 80° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole.
The meridian 160° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole.
The meridian 45° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Greenland, the Atlantic Ocean, South America, the Southern Ocean, and Antarctica to the South Pole.
The meridian 135° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole.
The meridian 15° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Europe, Africa, the Atlantic Ocean, the Southern Ocean, and Antarctica to the South Pole.
The meridian 15° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Greenland, Iceland, the Atlantic Ocean, Africa, the Southern Ocean, and Antarctica to the South Pole.
The meridian 35° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Europe, Asia, Africa, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole.
The meridian 55° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Europe, Asia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole.
The meridian 75° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole.
The meridian 125° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole.
The meridian 155° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Pacific Ocean, Australasia, the Southern Ocean, and Antarctica to the South Pole.
The meridian 165° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole.
The meridian 175° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Pacific Ocean, New Zealand, the Southern Ocean, and Antarctica to the South Pole.
The meridian 145° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole.
