The Royal Observatory, Greenwich (formerly the Royal Greenwich Observatory or RGO), in London, England played a major role in the history of astronomy and navigation, and is best known as the location of the prime meridian. It is situated on a hill in Greenwich Park, overlooking the River Thames.
The observatory was commissioned in 1675 by King Charles II, with the foundation stone being laid on 10 August. At this time the king also created the position of Astronomer Royal (initially filled by John Flamsteed), to serve as the director of the observatory and to "apply himself with the most exact care and diligence to the rectifying of the tables of the motions of the heavens, and the places of the fixed stars, so as to find out the so much desired longitude of places for the perfecting of the art of navigation." The building was completed in the summer of 1676. The building was often given the title "Flamsteed House".
The scientific work of the observatory was relocated elsewhere in stages in the first half of the 20th century, and the Greenwich site is now maintained as a tourist attraction.
Greenwich Mean Time (GMT) was at one time based on the time observations made at Greenwich (until 1954). Thereafter, GMT was calculated from observations made at other observatories which were still active. GMT is now often called Universal Time, which is now calculated from observations of extra-galactic radio sources, and then converted into several forms, including UT0 (UT at the remote observatory), UT1 (UT corrected for polar motion), and UTC (UT in discrete SI seconds within 0.9 s of UT1). To help others synchronise their clocks to GMT, a time ball was installed by Astronomer Royal John Pond in 1833. It still drops daily to mark the exact moment of 1 pm (13:00) year round (GMT during winter and BST during summer).
THANK YOU for taking Duckie to London with you, Vangie Austin!