Prime Meridian

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.

Why was the Prime Meridian established at Greenwich?

In 1675, the Royal Observatory at Greewich, outside of London was created to study the determination of longitude (a vital component to oceanic navigation). The United Kingdom and, by association, the United States, used Greenwich as the reference point for longitude.

Thus, by the time of an international conference in 1884 to establish fixed degrees of longitude on the planet, many countries had been using Greenwich as the prime meridianfor decades so the tradition became internationally accepted.