Royal Greenwich Observatory
Royal Greenwich Observatory, astronomical observatory established in 1675 by Charles II of England; formerly known as the Royal Observatory and located at Greenwich, it moved to Herstmonceux Castle, Sussex, in 1946. In the 1990 new headquarters at Cambridge were opened. Its equipment includes the 98-in. (248.9-cm) Isaac Newton reflecting telescope, 36-in. (91.4-cm) and 30-in. (76.2-cm) reflecting telescopes, 26-in. (66-cm) and 13-in. (33-cm) refracting telescopes, and an 8-in. (20.3-cm) reversible transit circle. The observatory is administratively responsible for the Radcliffe Observatory, Pretoria, South Africa, where there is a 74-in. (188-cm) reflector. The Royal Greenwich Observatory also includes the Nautical Almanac Office, which publishes the national navigational almanacs, and is responsible for the national time service, on which is based the worldwide system of time zones. The zero meridian, from which longitude is measured, passes through the observatory's former location at Greenwich. Other principal programs include measurement of the proper motions and radial velocities of stars, studies of the dynamics of the solar system and the Milky Way, and studies of the abundances of chemical elements in stars. From the appointment of John Flamsteed as its first director until 1972, the director of the observatory held the title of astronomer royal. Among the noted directors have been Flamsteed, Edmond Halley, James Bradley, Nevil Maskelyne, G. B. Airy, and E. Margaret Burbidge, who was the first director not to be astronomer royal.