Royal Observatory , Greenwich

The Royal Observatory was founded by Charles II in 1675. Charles II appointed John Flamsteed as his first Astronomer Royal in March 1675. The Observatory was built to improve navigation at sea and 'find the so-much desired longitude of places'. This was inseparable from the accurate measurement of time, for which the Observatory became generally famous in the 19th century. The Royal Observatory is also the source of the Prime Meridian of the world, Longitude 0° 0' 0''. The Prime Meridian is defined by the position of the large 'Transit Circle' telescope in the Observatory's Meridian Building. This was built by Sir George Biddell Airy, the 7th Astronomer Royal, in 1850. The cross-hairs in the eyepiece of the Transit Circle precisely define Longitude 0º for the world. Since the late 19th century, the Prime Meridian at Greenwich has served as the co-ordinate base for the calculation of Greenwich Mean Time. The Greenwich Meridian was chosen to be the Prime Meridian of the World in 1884. In 1960, shortly after the transfer of the Royal Greenwich Observatory (RGO) to Herstmonceux (and later Cambridge), Flamsteed House was transferred to the National Maritime Museum's care and over the next seven years the remaining buildings on the site were also transferred and restored for Museum use. Following the closure of the RGO at Cambridge in October 1998, the site is now again known as the Royal Observatory, Greenwich.