An observatory founded in 1675 at Greenwich, southeast London. After World War II it relocated to Herstmonceux Castle, Sussex, where it operated the Isaac Newton Telescope from 1967 to 1979. The original building at Greenwich is now maintained as a museum under the name Royal Observatory Greenwich (ROG). In 1990 the RGO moved again, this time to Cambridge, but was closed for good in 1998. The Time Department, which formerly maintained and distributed Greenwich Mean Time, was closed in 1990 before the move to Cambridge.