The foundation stone of the Royal Observatory, Greenwich, was laid

At 3:14 p.m. on 10 August 1675, the first Astronomer Royal, John Flamsteed, laid the foundation stone of the new Royal Observatory on a hill in Greenwich, London. King Charles II had commissioned it months earlier, charging Flamsteed to map the heavens “so as to find out the so-much desired longitude of places” for navigation at sea.

The building, Flamsteed House, was designed by Sir Christopher Wren — better known for St Paul’s Cathedral, but also a professor of astronomy. Money was tight: surplus bricks, wood, and iron were scavenged from a demolished gatehouse at the Tower of London.

The whole project was funded for the princely sum of £520.

The observatory’s careful timekeeping eventually made Greenwich the world’s reference point. In 1884, an international conference adopted the Greenwich Meridian as the planet’s prime meridian, fixing zero degrees longitude — and Greenwich Mean Time — through the spot where Flamsteed once squinted at the stars.