Which meridian is internationally recognized as 0° longitude?

The Prime Meridian is the internationally recognized meridian at 0° longitude.

The modern reference meridian passes through the Royal Observatory in Greenwich, London, and divides east and west longitude. It forms the starting point for measuring longitude around Earth, while the Equator is the starting reference for latitude.

An international conference held in Washington, D.C., in 1884 selected the Greenwich meridian as the world’s prime meridian. Twenty-five nations participated, and the decision reflected the widespread use of British nautical charts and the Greenwich meridian in navigation. Modern satellite-based reference systems place the official zero-longitude line about 102 metres east of the historic Airy Transit Circle at Greenwich.

The Prime Meridian should not be confused with the International Date Line, which lies roughly opposite it in the Pacific and marks a change of calendar date. The meridian itself is an imaginary half-circle running from the North Pole to the South Pole.