Accession Number:

ADA625074

Title:

Why the Greenwich Meridian Moved

Descriptive Note:

Journal article

Corporate Author:

NAVAL OBSERVATORY WASHINGTON DC

Report Date:

2015-08-01

Pagination or Media Count:

11.0

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 102m 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 lHeure 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 zero longitude lines at Greenwich, the orientation of the meridian plane used to measure Universal Time has remained essentially unchanged.

Subject Categories:

  • Geodesy

Distribution Statement:

APPROVED FOR PUBLIC RELEASE