Which observatory 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 in London, primarily to improve astronomical observations and navigation. Astronomer John Flamsteed became its first Astronomer Royal.

For many years, the meridian passing through the observatory’s Airy Transit Circle was treated as zero degrees longitude. International delegates formally adopted the Greenwich meridian as the world’s prime meridian at the International Meridian Conference in Washington, D.C., in 1884.

Modern satellite-based geodesy defines zero longitude slightly east of the historic instrument line, by about 102 meters, because Earth-centered reference systems differ from the old astronomical calculation. Nevertheless, Greenwich remains the cultural and historical reference associated with zero longitude and Greenwich Mean Time.