Prime Meridian

The Prime Meridian is the meridian (line of longitude) passing through the Royal Greenwich Observatory, Greenwich, England; it is the meridian at which longitude is 0 degrees. It is often referred to as the Greenwich Meridian.

Related Topics:
Meridian - Longitude - Royal Greenwich Observatory - Greenwich - England

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The meridian was agreed upon in October 1884. 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. France abstained when the vote was taken, and the French would cling to the Paris Meridian for several decades.

Related Topics:
1884 - U.S. President - Chester A. Arthur - Washington, D.C. - International Meridian Conference - Paris Meridian

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The International Date Line is on the opposite side of the world from the Prime Meridian.

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The zero meridian used by satellite navigation systems (on the WGS84 datum) is about 100 metres to the east of the line marked at Greenwich. It is not fixed on the ground as the continents are moving because of continental drift, and the WGS84 datum is an average of the various continental movements - the datum stays where it is and the continents slide around underneath it. (Otherwise a minor earthquake in Greenwich could change longitudes throughout the world.) The zero meridian used by the Ordnance Survey (OSGB36 datum) is about six metres to the west of the line marked at Greenwich. This was the standard meridian before 1851, and the Ordnance Survey simply carried on using it.

Related Topics:
WGS84 - Ordnance Survey - OSGB36

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Universal Time is calculated for a notional meridian which is near the WGS84 meridian.

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