Why the Greenwich meridian moved

Abstract

In 1884, the International Meridian Conference recommended that the prime meridian "to be employed as a common zero of longitude and standard of time-reckoning throughout the globe" pass through the "centre of the transit instrument at the Observatory of Greenwich". Today, tourists visiting its meridian line must walk east approximately 102 m before their satellite-navigation receivers indicate zero longitude. This offset can be accounted for by the difference between astronomical and geodetic coordinates-deflection of the vertical-in the east-west direction at Greenwich, and the imposed condition of continuity in astronomical time. The coordinates of satellite-navigation receivers are provided in reference frames that are related to the geocentric reference frame introduced by the Bureau International de l'Heure (BIH) in 1984. This BIH Terrestrial System provided the basis for orientation of subsequent geocentric reference frames, including all realizations of the World Geodetic System 1984 and the International Terrestrial Reference Frame. Despite the lateral offset of the original and current zerolongitude lines at Greenwich, the orientation of the meridian plane used to measure Universal Time has remained essentially unchanged.

Realizing a terrestrial reference frame using the Global Positioning System

“…The Z axis points in the direction of the mean pole (1984.0), and the X axis passes through the resulting equator near the Greenwich meridian. (The IERS reference meridian is approximately 100 m east of the Greenwich Meridian established by Sir George Airy in 1851 and represented by a brass strip at the Old Royal Observatory [Malys et al, 2015].) The ITRS must somehow accommodate the continuous movements of the Earth's fragmented crust that are fueled by plate tectonics.…”

'I think I discovered a military base in the middle of the ocean' -- Null Island, the most real of fictional places

“…) In this way the location of Null Island is arbitrary and is dependent upon the WGS84 datum and geographic coordinate system that arbitrarily chose its prime meridian. Contrary to popular belief, the meridian crossing the Royal Observatory in Greenwich is located 102 m west from the zero meridian used by modern satellite navigation receivers, that use geocentric reference frames, and their realizations of the WGS84 and the International Terrestrial Reference Frame (ITRF) (Malys et al 2015). Subsequently Null Island's location is also laterally offset from the Greenwich meridian historically referred to as "the prime meridian of the World".…”

“I Think i Discovered a Military Base in the Middle of the Ocean”—Null Island, the Most Real of Fictional Places

“…In this way the location of Null Island is arbitrary and is dependent upon the WGS84 datum and geographic coordinate system that arbitrarily chose its prime meridian. Contrary to popular belief, the meridian crossing the Royal Observatory in Greenwich is located 102 m west from the zero meridian used by modern satellite navigation receivers, that use geocentric reference frames, and their realizations of the WGS84 and the International Terrestrial Reference Frame (ITRF) [58]. Subsequently Null Island's location is also laterally offset from the Greenwich meridian historically referred to as "the prime meridian of the World".…”