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Greenwich Mean Time ... even the Greenwich meridian itself is not quite what it used to be—defined by "the centre of the transit instrument at the Observatory at ...
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.
The Prime Meridian of these modern reference systems is the IERS Reference Meridian, in full the International Earth Rotation and Reference Systems Service Reference Meridian (in short called the IRM), which is 102.5 metres east of the Airy Greenwich astronomical meridian represented by the stainless steel strip, which is now 5.31 arcseconds west.
The most important reason for the 5.3 seconds of longitude offset between the IERS Reference Meridian and the Airy transit circle is that the observations with the transit circle were based on the local vertical, while the IERS Reference is a geodetic longitude, that is, the plane of the meridian contains the center of mass of the Earth.
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]
The subject to discuss was the choice of "a meridian to be employed as a common zero of longitude and standard of time reckoning throughout the world". [1] It resulted in the recommendation of the Greenwich Meridian as the international standard for zero degrees longitude. [1]
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In 1870, Charles F. Dowd proposed four time zones based on the meridian through Washington, DC for North American railroads. [4] In 1872 he revised his proposal to base it on the Greenwich meridian. Sandford Fleming, a Scottish-born Canadian engineer, proposed worldwide Standard Time at a meeting of the Royal Canadian Institute on February 8 ...