What is the Royal Observatory Greenwich?
The Royal Observatory Greenwich is a historic astronomical observatory in southeast London, founded in 1675 by King Charles II. It is home to the Prime Meridian, the line of zero degrees longitude, and Greenwich Mean Time.
The observatory was established to improve navigation at sea by mapping the positions of stars. The first Astronomer Royal, John Flamsteed, worked in Flamsteed House, designed by Sir Christopher Wren.
In 1884, an international conference chose the meridian passing through Greenwich as the Prime Meridian of the world. This made Greenwich the reference point for world time and longitude.
Standing on the meridian
Visitors can stand with one foot in the Eastern Hemisphere and one in the Western Hemisphere on the Prime Meridian line in the courtyard.
The red time ball on top of Flamsteed House drops at 1pm every day. It was introduced in 1833 so that ships on the River Thames could set their clocks accurately.
The observatory is part of Royal Museums Greenwich, along with the National Maritime Museum, the Queen's House and the Cutty Sark. The Peter Harrison Planetarium offers shows about the universe. Maritime Greenwich is a World Heritage Site.