The Greenwich Royal Observatory, or The Royal Observatory, Greenwich as it is currently known was founded in 1675 under King Charles II. Until its official closing as a scientific institute in 1998, it was the oldest in Great Britain still in operation.
It was Sir Jonas Moore, Surveyor General for King Charles II, who first proposed the building of the observatory and it furnished the buildings with equipment and instruments with his own money. The final site was on the foundation of the old Duke Humphrey Tower, not the most ideal spot, being aligned 13 degrees from true North, but all that could be afforded on the £500 budget.
John Flamsteed was the first person to serve as director of the Greenwich Royal Observatory and first to hold the title of Astronomer Royal, which came with the directorship. Flamsteed immediately went to work on his new stellar tables and charts.
The Royal Greenwich Observatory was also a time-keeper. It housed two of the most accurate clocks of the time, having a margin of error of +/- 7 seconds per day. Since 1833 a Time Ball on top of the Octagonal Room of the observatory rises halfway up the mast at 12:55, fully at 12:58, and falls at 13:00 hours every day and provided a central time for ships on the Thames to set their clocks by. Later, a telegraph cable would link this time ball to a sister on the southeast coast that would be used by ships in the English Channel. In 1928, Greenwich Time was chosen as the base of world time and given the name Universal Time.
In 1884, The Royal Greenwich Observatory was adopted as the site of 0 degrees for longitudinal measurement – the Prime Meridian, which had been established locally years before in 1851. The Prime Meridian was originally marked through the courtyard grounds with a brass strip, which since has been replaced with stainless steel and since 1999 there is a large green laser pointing north over London.