Royal Observatory Greenwich was founded on 10 August 1675

The Royal Observatory, Greenwich, was founded at 3:14 p.m. on 10 August 1675, when the first Astronomer Royal, John Flamsteed, laid its foundation stone on the highest ground in Greenwich Park, London. Royal Museums Greenwich describes it as Britain’s first state-funded scientific research institution.

Its purpose was practical: finding longitude at sea. The road to the ceremony was short:

• December 1674: a French visitor, the Sieur de St Pierre, claims at court that the Moon’s position against the stars could fix a ship’s position.
• February 1675: English scholars reject his scheme, but the idea sticks.
• 4 March 1675: Charles II appoints Flamsteed his “astronomical observator”.
• June 1675: the king orders a small observatory built “upon the highest ground” in Greenwich Park.

The horoscope behind the date

Flamsteed cast a horoscope to find the best date for starting construction, and the chart survives in the Royal Museums Greenwich collection. He was perhaps imitating Tycho Brahe, who had done the same for his Uraniborg observatory in 1576. Flamsteed himself was wary of being linked with astrology, which by then smelled of quackery.

The Crown was less generous than the ceremony implies. Flamsteed’s salary was £100 a year, from which he paid £10 in tax and had to buy all his own instruments. Christopher Wren, a former Oxford astronomy professor, designed the building with Robert Hooke on the old foundations of Greenwich Castle, and Flamsteed moved in on 10 July 1676.

Over the next 40 years Flamsteed made more than 50,000 observations of the Moon and stars, compiled after his death into the Historia Coelestis Britannica (1725), the standard star catalogue for a century. That work made Greenwich the navigators’ reference point: by the 1880s nearly two-thirds of the world’s ships used Greenwich-based charts, so the 1884 International Meridian Conference chose it as 0° longitude.