One of the fundamental problems facing early navigators was the problem of longitude. Ancient navigators had been able to figure out latitude by measuring how far the pole star was in the sky. It is a simple matter of using a sextant to measure the angle.
Determining longitude, however, was extremely challenging. Even if sailors knew how far north or south they were, if they didn't know where they were east or west, they could end up hundreds of miles off course, or worse, washed up on jagged rocks.
Longitude vexed sailors for centuries. In 1714, Parliament passed the Longitude Act and established a £20,000 prize for anyone who could solve the problem of longitude.
The solution to the latitude problem was solved by Englishman John Harrison. His solution didn't involve astronomy, but rather involved the accurate keeping of time. By keeping a clock set to noon at the port of departure, you could tell how far you traveled east to west by calculating the time difference of local noon.
One the ability to keep accurate time on the high seas was established, it was then necessary to establish a longitudinal line of reference. Unlike the equator which is a natural reference point for latitude, there is no natural reference point for longitude. The British Navy used the Royal Observatory in Greenwich as their meridian of reference.
As the British Empire expanded in influence, especially in all matters naval, it became the default meridian for many seaman around the world. In 1884 at the behest of the President of the United States, the International Meridian Conference was convened in Washington, DC and Greenwich was chosen as the International Prime Meridian, and midnight at Greenwich would be the basis of the Mean Solar Day or Greenwich Mean Time (GMT or now UTC).
Today, the Royal Greenwich Observatory and the National Maritime Museum is open to the public and was granted status as a UNESCO World Heritage Site. The Greenwich Observatory is now a museum which contains some of the prized possessions in the history longitude: John Harrison's original time keeping devices.
One of the most popular things to do for tourists is to stand astride the Prime Meridian, technically standing in both the eastern and western hemispheres at the same time. (eg: the middle of the Earth!) You can also witness the ball drop at the top of the Greenwich Observatory at 1pm every day, a tradition which has occurred every day since 1833. The tradition of dropping a ball at midnight in Times Square New York harkens back to the tradition which started in Greenwich.
The Greenwich Observatory and Naval History Museum are easy to reach from Central London. Just take the train to the Greenwich station and it is about a 10 minute walk to the Greenwich historical sites.
Gary Arndt is an American travel blogger who has been traveling around the world non-stop since March 2007. He has visited over 80 countries and territories. You can follow his adventures on his travel blog or on Twitter or Facebook.