Greenwich's Prime Meridian Drifts 102 Meters East in the GPS Era
The brass line at Greenwich marks the historical Prime Meridian, but GPS-based coordinates place zero longitude about 102 metres east of that marker due to a shift in reference frames in 1984. The Airy Transit Circle defined the original meridian, but modern satellite geodesy uses a center-of-Earth frame, so the marker is now a historical symbol rather than the true zero line. Tourists continue to photograph it, and the observatory preserves it for heritage reasons.