Stand on the Prime Meridian Line

Since the late 19th century, the Prime Meridian at Greenwich has divided the eastern and western hemispheres of the Earth - just as the equator divides the northern and southern hemispheres. When you stand across the line, you have one foot in the east and one in the west!

Until the 1880s, countries used their own meridian lines for mapmaking and navigation. This meant there was no globally agreed way of measuring distances and plotting locations east and west.

In 1884, different nations gathered in Washington D.C. to choose one single meridian as a common reference. After weeks of discussion, delegates voted to make the Greenwich Meridian the world's Prime Meridian.

Greenwich was chosen because its measurements were already used by most of the world's seafarers and mapmakers. Thanks to the work of generations of astronomers, the Royal Observatory became the home for global time and navigation.

From pole to pole, the Prime Meridian covers a distance of 20,000 km. 

In the northern hemisphere, the Prime Meridian passes through the UK, France and Spain in Europe, and Algeria, Mali, Burkina Faso, Togo and Ghana in Africa. The only land crossed by the Meridian in the southern hemisphere is Antarctica.

In Greenwich the Prime Meridian is marked by a metal line fixed into the Royal Observatory courtyard, and at night by a laser beam. Depending on the weather, the beam can be seen from more than 20 km away.

From John Harrison's revolutionary timekeepers to the Great Equatorial Telescope, the Royal Observatory is home to some of the UK's most prized scientific instruments. See them all on display as you walk round the historic buildings.

The Meridian Courtyard also offers some of the best views in London, high above the trees of Greenwich Park.

Finally, did you know that astronomers still work at the Royal Observatory today? Join them on an inspiring journey into space at London’s only planetarium.