Royal Observatory

The observatory was proposed in 1674 by Sir Jonas Moore, who in his role as Surveyor-General of the Ordnance persuaded Charles II to create it. The King founded it on 22 June 1675 and appointed John Flamsteed the first Astronomer Royal, charged with rectifying the tables of the motions of the heavens "so as to find out the so much desired longitude of places for the perfecting of the art of navigation". Christopher Wren chose the hilltop in Greenwich Park where Greenwich Castle had stood as a Tudor hunting lodge; the park was a royal estate, so no new land had to be bought.

Construction began on 10 August 1675 and the building was completed in the summer of 1676. Wren designed it, probably assisted by Robert Hooke, and it was the first purpose-built scientific research facility in Britain. It cost £520, and was raised largely from recycled materials on the foundations of Duke Humphrey's Tower, which left it aligned 13 degrees away from true north, somewhat to Flamsteed's chagrin. Moore supplied the key instruments at his own cost and gave two Thomas Tompion clocks for the Octagon Room, accurate to seven seconds a day, then unparalleled.

Tycho Brahe's thousand-star catalogue of 1598, one of the best then available, was not accurate enough to determine longitudes, and Flamsteed's first order of business was better charts. James Bradley, the third Astronomer Royal, whose tenure began in 1742, charted sixty thousand stars between 1750 and 1762 so accurately that his catalogues were still in use in the 1940s. Nevil Maskelyne, the fifth holder of the office, began publishing The Nautical Almanac from Greenwich observations in 1767. Oversight passed from the Board of Ordnance to the Admiralty in 1818, with the observatory charged to maintain the Royal Navy's marine chronometers. George Biddell Airy, Astronomer Royal from 1835, set about getting better instruments; the transit circle he installed in 1851 served positional astronomy for a century.

In 1833 the Astronomer Royal John Pond installed a time ball to help mariners at the port and others in line of sight synchronise their clocks: a five-foot ball of wood and leather, built by Messrs Maudslay and Field for £180 and dropped precisely at one o'clock. From 1852 an electric impulse from the Shepherd Master Clock released it, and in the same year time signals began going out along the telegraph wires.

The meridian running through Airy's transit circle, first used in 1851, was adopted as the Prime Meridian for the whole world at the International Meridian Conference in Washington on 22 October 1884, the vote taken on the 13th.

On 15 February 1894 a bomb detonated accidentally in Greenwich Park near the observatory building while it was being held by Martial Bourdin, a 26-year-old French anarchist, who died about thirty minutes later. It is not known why he chose the observatory, or whether the explosion was intended to occur elsewhere; Joseph Conrad used the incident in his 1907 novel The Secret Agent. On 15 October 1940 a direct hit during the Blitz destroyed the Courtyard gates and brought down the wall above the Gate Clock, damaging its dial, which was repaired after the war.

Light pollution in London prompted the decision, taken in 1947, to move the Royal Observatory to Herstmonceux Castle in East Sussex. The Astronomer Royal Harold Spencer Jones went there in 1948, the scientific staff followed when the buildings were finished in 1957, and the Greenwich site was renamed the Old Royal Observatory. The institution moved on to Cambridge in 1990, and its funding body, the Particle Physics and Astronomy Research Council, decided to close it by 1998. The Astronomer Royal Martin Rees called the council "irresponsible" for its handling of the RGO.

Greenwich took back its original name in 1998 as part of the National Maritime Museum, and in 2011 the Greenwich museums became collectively the Royal Museums Greenwich. The buildings hold John Harrison's H4 chronometer and his three earlier marine timekeepers, all four the property of the Ministry of Defence, and the 28-inch Grubb refractor of 1893, the largest of its kind in the UK. A £16 million redevelopment begun in February 2005 reopened on 25 May 2007 with the 120-seat Peter Harrison Planetarium, and the Annie Maunder Astrographic Telescope, four instruments and site works costing about £150,000, had achieved first light by June 2018. The site has been a Grade I listed building since 8 June 1973 and is a scheduled monument.