Royal Observatory Greenwich

Where Time and Longitude Were Born

Founded in 1675 by King Charles II and designed by Sir Christopher Wren, the Royal Observatory was created to solve the critical problem of longitude at sea. Its original purpose was to map the stars with such precision that sailors could determine their position and avoid disastrous shipwrecks. Over centuries, it became the heart of British astronomy and the keeper of time itself. The observatory’s work laid the foundation for Greenwich Mean Time (GMT), which in 1884 was adopted as the world’s Prime Meridian, dividing east from west and shaping the global time zone system we still use today.

Walking the Meridian and the Great Equatorial Telescope

The most famous moment for most visitors is standing on the Meridian Line in the courtyard, with one foot in the eastern hemisphere and one in the western. This line, defined by the Airy Transit Circle telescope, became the global reference for zero degrees longitude. Nearby, the Great Equatorial Telescope, housed in its distinctive onion dome, is one of the UK’s largest historic refractors. Visitors can step inside to appreciate its scale and learn how it helped astronomers peer deeper into the universe. The observatory also preserves the original Time Ball, which has dropped daily at 1pm since 1833, once signaling the exact time to ships on the Thames.

Timekeepers, Instruments and the Octagon Room

Inside Flamsteed House, the Time Galleries trace the evolution of navigation and timekeeping, with a highlight being John Harrison’s revolutionary marine chronometers. These precision clocks solved the longitude problem and transformed maritime safety. The Octagon Room, the oldest part of the observatory, was Wren’s elegant solution for a stable, level platform for astronomical instruments. Today, it’s a beautifully preserved space where visitors can imagine 17th-century astronomers at work, surrounded by period instruments and clocks. The museum also displays a 4.5-billion-year-old meteorite and other fascinating astronomical and navigational tools.

A Hilltop with a View and a Modern Astronomy Hub

Beyond the historic buildings, the Observatory sits at the top of Greenwich Park, offering one of London’s most celebrated panoramic views. From the hill, the skyline unfolds with the River Thames, the City of London, Canary Wharf, and the dome of St Paul’s Cathedral. The site now also functions as a modern astronomy centre, with interactive galleries and live science demonstrations that bring space and the cosmos to life for all ages. While the Peter Harrison Planetarium is currently closed for a major renovation, the observatory continues to host talks, tours, and hands-on activities that deepen the experience of astronomy and the history of time.