The Royal Observatory was founded on 22 June 1675 by Charles II. It was built to observe the stars which were very important in helping sailors find their way at sea. Charles II appointed John Flamsteed as his first Astronomer Royal.
The 28-year-old clergyman was instructed to do work which would help to solve the problem of finding longitude - one's exact position east and west - while at sea and out of sight of land. Longitude was then impossible to calculate at sea and Flamsteed began his observations in 1676 to solve the longitude problem once and for all. The work of the astronomers at Greenwich helped many ships to navigate the world's seas of the safely.
The time-ball was added in 1833. Sailors used to set their marine chronometers (clocks) before they sailed. The time-ball is still dropped at one o'clock every day and could clearly be seen by all ships on the Thames. In 1960 the Royal Observatory was transferred to the National Maritime Museum's care and later opened to the public as a museum. Here the collections of scientific, especially astronomical, instruments has continued to grow.