Prime meridian (Greenwich)

This article is about a historical prime meridian. For the general concept and information on modern prime meridians, see prime meridian.

Prime meridian marked at the Royal Observatory Greenwich

Laser projected from the Royal Observatory in Greenwich marking the Prime meridian

A GPS receiver at the prime meridian. This does not indicate a longitude of zero because the GPS reference meridian is about 100 metres to the east.

The prime meridian, based at the Royal Observatory, Greenwich, 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 maps. In October of that year, at the behest of U.S. President Chester A. Arthur, 41 delegates from 25 nations met in Washington, D.C., USA, 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.

The prime meridian passes through the Airy transit circle (51°28′40.1247″N 0°0′5.3101″W) of the Greenwich observatory. It was long marked by a brass strip in the courtyard, now upgraded to stainless steel, and, since 16 December 1999, has been marked by a powerful green laser shining north across the London night sky.

The Greenwich meridian passes through the United Kingdom, France, Spain, Algeria, Mali, Burkina Faso, Togo, Ghana, and Queen Maud Land in Antarctica.

See also

• Greenwich Mean Time
• United Kingdom Ordnance Survey Zero Meridian

External links

• "Where the Earth's surface begins—and ends", Popular Mechanics, December 1930
• International Conference Held at Washington for the Purpose of Fixing a Prime Meridian at Project Gutenberg
• A pictorial catalogue of meridian markers