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The Greenwich meridian is a prime meridian, a geographical reference line that passes through the Royal Observatory, Greenwich, in London, England. [1] From 1884 to 1974, the Greenwich meridian was the international standard prime meridian, used worldwide for timekeeping and navigation.
This old astronomical prime meridian has been replaced by a more precise prime meridian. When Greenwich was an active observatory, geographical coordinates were referred to a local oblate spheroid called a datum known as a geoid, whose surface closely matched local mean sea level. Several datums were in use around the world, all using different ...
The prime meridian of the Moon lies directly in the middle of the face of the Moon visible from Earth and passes near the crater Bruce. The prime meridian of Mars was established in 1971 [35] and passes through the center of the crater Airy-0, although it is fixed by the longitude of the Viking 1 lander, which is defined to be 47.95137°W. [36]
See § De facto and de jure date lines below, and map above at right. The IDL is roughly based on the meridian of 180° longitude, roughly down the middle of the Pacific Ocean, and halfway around the world from the IERS Reference Meridian, the successor to the historic Greenwich prime meridian running through the Royal Greenwich Observatory. In ...
The United Kingdom Ordnance Survey Zero Meridian is the prime meridian used by the Ordnance Survey (OSGB36 datum). It is about six metres to the west of the Airy meridian marked at Greenwich . When the first Ordnance Survey map was published in 1801, the official Prime Meridian of Great Britain was the one established by the third Astronomer ...
The International Meridian Conference was a conference held in October 1884 in Washington, D.C., in the United States, to determine a prime meridian for international use. [1] The conference was held at the request of U.S. President Chester A. Arthur . [ 1 ]
The astronomic prime meridian at Greenwich, England. The geodetic prime meridian is actually 102.478 meters east of this point since the adoption of WGS84. Toward the ending of the 12th century there were two main locations that were acknowledged as the geographic location of the meridian, France and Britain.
The prime meridian defines 0° longitude; by convention the International Reference Meridian for the Earth passes near the Royal Observatory in Greenwich, south-east London on the island of Great Britain. Positive longitudes are east of the prime meridian, and negative ones are west.