Why astronomers created Greenwich Mean Time 🕛️ For centuries, humans have relied on the sun for timekeeping. You can tell from its height above the horizon and its position roughly how many hours of daylight you have. And for most people, that's fine. But for astronomers, solar time is too variable, It's incredibly inaccurate and not exactly 24 hours. This is why astronomers at the Royal Observatory Greenwich created an average or mean day of exactly 24 hours. So Greenwich Mean Time is solar ti

Discover the clocks that changed the world and stand on the world-famous Prime Meridian Line at the home of GMT this spring. | Royal Museums Greenwich