Greenwich Observatory
The Royal Observatory at Greenwich occupies a hill in southeast London's Greenwich Park and holds a unique place in scientific and navigational history. Founded in 1675 by King Charles II, the observatory was established with a very specific practical purpose: to solve the problem of determining longitude at sea. In the age of sail, the inability to accurately calculate a ship's east-west position was a cause of catastrophic maritime losses, and the astronomers appointed here dedicated generations of work to solving it. The observatory was designed by Sir Christopher Wren, who adapted an existing structure to create the distinctive red-brick Flamsteed House that still stands at the summit of the park. The first Astronomer Royal, John Flamsteed, began the painstaking work of cataloguing star positions that would eventually help navigators establish their longitude. His successors continued and refined this work for centuries, producing star charts and time signals that became essential to maritime navigation worldwide. The observatory's role in timekeeping led to a development of global significance. In 1884, at an international conference in Washington D.C., the meridian passing through Greenwich was adopted as the Prime Meridian of the world, the zero line of longitude from which all geographic positions east and west are measured. Greenwich Mean Time became the foundation of global timekeeping, a convention that persists in the modern digital age through Coordinated Universal Time. Visitors today can stand astride the famous brass meridian line embedded in the courtyard, placing one foot in the eastern hemisphere and one in the western. The site's collection of historic astronomical instruments is genuinely extraordinary, including telescopes used by generations of astronomers and original clockwork mechanisms that helped synchronise time signals across the British Empire. The Great Equatorial Telescope, housed under its green onion dome, was the largest telescope in Britain when it was installed in 1893. The iconic red Time Ball on top of Flamsteed House has dropped at precisely 13:00 every day since 1833, providing ships in the Thames with a visual time signal they could use to set their chronometers before setting sail. It still falls punctually today. The nearby Planetarium shows bring the universe to life for visitors of all ages. Entry to the grounds and the Prime Meridian courtyard is free. Paid admission covers access to the observatory buildings, exhibitions and the Planetarium. The hilltop location also provides one of the best panoramic views across the London skyline, taking in the skyscrapers of Canary Wharf, the dome of St Paul's Cathedral and the sweep of the Thames.