Prime Meridian

History and Overivew of the Prime Meridian

Prime Meridian Sign
The Prime Meridian line lies at the Greenwich Observatory in the London metropolitan area. Matt Rosenberg

The prime meridian is the zero degree line of longitude that passes near London. The prime meridian was officially established as zero degrees longitude at an international conference in 1884. While latitude has its zero degree line along the equator, an actual physical feature, longitude is not based on any physical feature of the earth and is not impacted by the sun or the earth’s orbit.

Prior to 1884, some countries utilized local “prime meridians” to establish their coordinate systems within their country and around the world.

In order to have any x,y system of coordinates, as latitude and longitude are, there must be a starting place for both the north-south and the east-west axes.

In the case of latitude, the choice is easy, zero degrees from the plane of the earth through its circumference is the equator and ninety degrees from the equator are the poles. All other degrees of latitude are actual degrees between zero and ninety based on the arc from the plane along the equator (imagine a protractor with the equator at zero degrees and the north pole at ninety degrees).

However, for longitude, there is no plane or place to start the counting of longitude so prior to 1884, some countries established their own local prime meridian. The United Kingdom and its former colonies established the Royal Observatory at Greenwich just outside of downtown London in 1675. This national observatory was established as the starting location for longitude or the y-axis for the British coordinate system.

Since the United Kingdom was a major colonial power and a major navigational power of the eighteenth and nineteenth centuries, their maps and navigational charts with the prime meridian passing through Greenwich were promulgated and many other countries adopted Greenwich as their prime meridians.

By 1884, international travel was commonplace and the need for a standardized prime meridian became readily apparent.

Forty-one delegates from twenty-five "nations" met in Washington D.C. for a conference to establish zero degrees longitude and the prime meridian.

Greenwich was selected as the prime meridian by a vote of twenty-two in favor, one against (Haiti), and two abstentions (France and Brazil). By the time of the conference, the United Kingdom and its colonies as well as the United States of America had already begun using Greenwich as the prime meridian; this weighed heavily on the selection process.

With the establishment of the prime meridian and zero degrees longitude at Greenwich, the conference also established time zones. By establishing the prime meridian and zero degrees longitude in Greenwich, the world was then divided into 24 time zones (since the earth takes 24 hours to revolve on its axis) and thus each time zone was established every fifteen degrees of longitude, for a total of 360 degrees in a circle.

The establishment of the prime meridian in Greenwich in 1884 permanently established the system of latitude and longitude and time zones that we use to this day. Latitude and longitude are used in GPS and is the primary coordinate system for navigation on the planet.