Greenwich Observatory Laid: Time Gets a Standard

King Charles II wanted to solve the deadliest puzzle in navigation: how to determine longitude at sea. On August 10, 1675, the foundation stone was laid for the Royal Observatory at Greenwich, a hilltop site east of London chosen by Sir Christopher Wren for its clear views of the sky. The observatory's mission was explicitly practical — to improve astronomical tables so that sailors could fix their position on the open ocean, a problem that had been killing crews and sinking ships for centuries. The man appointed to run it, John Flamsteed, became the first Astronomer Royal. His salary was £100 per year, and the crown provided almost nothing for instruments, forcing Flamsteed to purchase or build his own equipment. Despite the chronic underfunding that would characterize the observatory for much of its existence, Flamsteed spent the next 44 years compiling a catalog of more than 3,000 star positions with unprecedented accuracy. His work, Historia Coelestis Britannica, published posthumously in 1725, became the foundation for all subsequent astronomical navigation. The longitude problem itself was not solved by astronomers alone. While Flamsteed and his successors refined lunar distance tables that allowed navigators to calculate longitude from the moon's position, the practical breakthrough came from clockmaker John Harrison, who built a marine chronometer accurate enough to keep time at sea. The rivalry between the astronomical and chronometric approaches to longitude played out over decades, with the Board of Longitude eventually — and reluctantly — awarding Harrison his prize. Greenwich's legacy extends far beyond any single discovery. In 1884, the International Meridian Conference selected the Greenwich meridian as the world's prime meridian, making the observatory the literal reference point for global time and navigation. Every time zone on Earth is measured as an offset from Greenwich Mean Time. A foundation stone laid on a London hilltop for a modest astronomical workshop became the center from which humanity measures its position on the planet.