| the meridian running through Greenwich, England, from which longitude east and west is reckoned. |
prime meridian  (click for larger image in new window) n. The zero meridian (0°), used as a reference line from which longitude east and west is measured. It passes through Greenwich, England. |
prime meridian
imaginary line used to indicate 0 longitude that passes through Greenwich, a borough of London, and terminates at the North and South poles. An international conference held in Washington, D.C., in 1884 designated "the meridian passing through the centre of the transit instrument at the Observatory of Greenwich as the initial meridian for longitude." The observatory (renamed the Royal Greenwich Observatory) was moved to Hailsham, East Sussex, during the 1950s, but the original site continues to serve as the location for 0 longitude.
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