Why did the Greenwich Meridian move

    Nominal Meridian (dashed line) and Official Zero Meridian in the ITRF system (solid line)

    In October 1884, the International Meridian Conference was held in Washington, the participants of which chose a meridian suitable for use as a common zero longitude and a standard for calculating time around the world. It was decided that the Zero Meridian will pass through the center of the Greenwich Observatory Passing Instrument.

    But these days, tourists have to go east about 102 meters before the GPS navigator shows zero longitude.

    The reasons for this phenomenon were studied by a team of specialists from the US National Geospatial Intelligence Agency, Analytical Graphics, the astronomical department of the University of Virginia and the US Naval Observatory. They publisheda scientific article in the August issue of the Journal of Geodesy.

    The difference between the coordinates of the zero meridian is explained by the difference between the astronomical and geodetic coordinates. Satellite navigators receive information on the geocentric reference scheme, which was approved by the International Bureau of Time in 1984. Adopted thirty years ago, the World Geodetic System and the International Earth Coordinate System (ITRS) and the International Earth Reference System (ITRF) have become standards in cartography, surveying and navigation systems, including GPS. In the ITRF system, the origin is the center of mass of the earth (including the ocean and atmosphere).

    The authors of the scientific work explain that astronomers of the 19th century simply made a mistake when calculating the zero meridian, because they did not have at their disposal high-precision equipment for compiling the gravitational model of the Earth. They did not take into account that the Earth has an irregular shape, and gravitational anomalies are present in the structure of the mantle.

    The gravitational anomaly in the Greenwich region led to errors in calculating the position of the meridian in the 19th century.

    “After the advent of new measurement technologies, the“ relocation ”of the zero meridian was inevitable. Maybe we should move or set up a new sign in Greenwich Park, where the new zero longitude is located, ” said Kenneth Seidelmann from the University of Virginia.

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