On 13 October 1884 Greenwich, in London was established as the Universal Time meridian of longitude - from which all World time zones are based. The Royal Observatory Greenwich is where East meets West at the Greenwich Meridian Line (0° longitude).
What is longitude?
Longitude is the location of a place east or west of a north-south line called theprime meridian. The Prime Meridian divides the Earth into the eastern and western hemisphere.
Why was Greenwich chosen?
There are an infinite number of possible meridians, each stretching from the North to the South Pole, and any one of these could have been chosen. However, the Greenwich Meridian was pre-eminent because it had already been adopted by both the UK and USA and was therefore being used by 72% of the world's shipping.