IERS Reference Meridian
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The IERS Reference Meridian, also called the International Reference Meridian, is the prime meridian maintained by the International Earth Rotation and Reference Systems Service. It passes about 5.3 a
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Prime meridian (Greenwich)
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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. From 1884 to 1974, the Greenwich meridian was the in
IERS Reference Meridian
…Service (IERS). It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle, and thus it differs slightly from the historical Greenwich Meridian. At the latitude of the Royal Observatory, Greenwich, the difference is 102 metres (335 ft). It is the reference meridian of the Global Positioning…
Laser projected from the Royal Observatory, marking the prime meridian of Greenwich
Tourists queuing to take pictures on the brass line marking the prime meridian at the Royal Observatory, Greenwich
A GPS receiver at the marking strip of the Greenwich Meridian in front of the Royal Observatory. The indicated longitude is not exactly zero because the geodetic zero meridian on a geocentric reference ellipsoid (which is what GPS positioning yields, using the IERS Reference Meridian) is 102 metres east of this strip.