Which 1884 conference established Greenwich as the world’s prime meridian?

The International Meridian Conference established Greenwich as the world’s prime meridian.

The conference met in Washington, D.C., in October 1884 to choose a common zero of longitude for international navigation and timekeeping. Twenty-five nations sent delegates. The participants adopted the meridian passing through the centre of the transit instrument at the Royal Observatory in Greenwich, England, as the initial meridian.

The decision made Greenwich the reference point for measuring longitude east and west around the globe. The conference also supported a universal day beginning at midnight and counted from the initial meridian, although implementation of every recommendation was not immediate. Greenwich Mean Time later became a major international time standard.

Modern geodesy uses the International Reference Meridian, which is slightly east of the historic Greenwich line because satellite-based measurements define Earth’s reference frames more precisely. Nonetheless, the 1884 conference’s Greenwich meridian remains the familiar historical basis for global maps, longitude, and the world’s time-zone system.