Prime meridian (Greenwich)

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

Coordinates: 51°28′40.12″N 0°00′05.31″W / 51.4778111°N 0.0014750°W / 51.4778111; -0.0014750

A group of people waiting in a line curving to the left on a cobblestone surface. Behind it is an ornate brick building with a red ball on top. The people at the end of the line, closest to the camera, are taking pictures of other people near a shiny metal monument on the right, under a tree. A line in the cobblestone connects them
Tourists taking pictures with the Prime Meridian monument
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.

A prime meridian, based at the Royal Observatory, Greenwich, in London,[1] 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 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. 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.[2]

The prime meridian passes through the Airy transit circle (51°28′40.1247″N 0°0′5.3101″W / 51.477812417°N 0.001475028°W / 51.477812417; -0.001475028 (Airy Transit)[3]) 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:

See also[edit]


  1. ^ ROG Learing Team (23 August 2002). "The Prime Meridian at Greenwich". Royal Museums Greenwich. Royal Museums Greenwich. Retrieved 14 June 2012. 
  2. ^ Malachy Postlethwayt. (1774) Universal Dictionary of Trade and Commerce. (4th edition) London: W. Strahan, J. & F. Rivington. Vol. 1 "A New and Correct Map of the Coast of Africa"
  3. ^ Calvert, Carl (1999). "The Greenwich Meridian in the Space Age". Retrieved 7 July 2011. 

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