Which Greenwich site gives its name to the prime meridian?

The Royal Observatory Greenwich gives its name to the prime meridian.

The observatory was founded in 1675 by King Charles II at Greenwich, London, to improve navigation at sea. Astronomers there measured the positions of stars and helped create accurate tables and clocks for determining longitude. The meridian passing through the observatory’s historic Airy Transit Circle became the reference line for 0 degrees longitude.

The International Meridian Conference in Washington, D.C., selected the Greenwich meridian as the worldwide prime meridian in 1884. Longitude is measured east or west from that line, while latitude is measured north or south from the Equator.

Modern satellite-based systems place the internationally defined zero longitude a little east of the historic observatory line, because Earth’s reference system is geocentric and uses later surveying methods. The traditional Greenwich meridian remains the familiar foundation of global timekeeping and map history.