Royal Greenwich Observatory

The meridian line at Greenwich in London, England. A meridian line is an imaginary line that runs from the North Pole to the South Pole. By international convention, the meridian line at Greenwich, which runs through the Royal Observatory telescope, marks 0° longitude and is the point from which all other lines of longitude are measured.

The Royal Greenwich Observatory (RGO) was founded in 1675 at Greenwich, East London, to provide navigational information to sailors. After World War II it moved to Herstmonceux Castle in Sussex, where the 2.5-m/8.2-ft Isaac Newton Telescope (INT) was constructed in 1967. Following the relocation of the INT to the island of La Palma, in the Canary Islands, RGO was relocated to Cambridge in 1988–90. In 1998 the Cambridge site was closed and the RGO merged with the Royal Observatory Edinburgh to form a new Astronomy Technology Centre on the Edinburgh site.

The observatory was founded by King Charles II. The eminence of its work resulted in Greenwich Time and the Greenwich Meridian being adopted as the international standard of reference in 1884.