The Meridian Line in Greenwich is the dividing point between the eastern and western hemispheres – Longitude 0°. You can stand on the Line at the Royal Observatory in Greenwich Park with one foot in each half of the earth.
The Meridian Line, or Prime Meridian, separates the eastern and western hemispheres just like the Equator separates the northern and southern. It’s been marked at Greenwich since 1884 in the courtyard of the Royal Observatory, where a stream of visitors take each other’s photograph standing on the line. It’s also marked by a green laser that stretches out across Greenwich every evening.
The Greenwich Meridian was chosen as the Prime Meridian of the World in 1884 by forty-one delegates from 25 nations. Only one nation voted against (San Domingo) although France remained unconvinced and kept their own Meridian in Paris until 1914.
We need a Prime Meridian to define zero longitude so that we can accurately determine where we are. If you measure how far you are from the Prime Meridian (Longitude) and how far you are from the Equator (Latitude) you can combine the results to pinpoint your place on the planet.
So if you want to impress your friends, when you stand on the Meridian line say: “Everywhere on Earth is measured from here” and look wise. They’ll definitely be impressed.