Imagine a world in which the maps of different countries do not start from the same line. Until the end of the 19th century, this was the reality: Paris, Cadiz, the Faroe Islands and national observatories served as separate prime meridians. Thus, the same point on Earth could have a different longitude depending on the map being used.
On October 13, 1884, the International Meridian Conference met in Washington to discuss a common zero point for measuring longitude and a standard for telling time. The meeting was convened by the United States and began on October 1. It was attended by 41 delegates from 25 countries.
Why Greenwich
The choice was not made in vain. The British Observatory in Greenwich already had enormous practical importance for navigation. Sailors used Greenwich time to calculate their position at sea, and British nautical charts were widely distributed. In 1879, about 65% of ships and 72% of ship tonnage used the Greenwich meridian as a reference point.
The development of railways and the telegraph made the differences between local times increasingly inconvenient. Timetables, communications and navigation required a common system that could operate across national boundaries.
“The Conference proposes to the governments represented that the meridian passing through the centre of the transit instrument at the Greenwich Observatory be adopted as the prime meridian of longitude“, the resolution adopted read.The decision was taken on 22 October
The date of 13 October is often associated with the choice of Greenwich because that is when the conference held one of its key meetings. However, the official vote was on 22 October 1884. The resolution was adopted by 22 votes “for“, one “against“ and two abstentions. San Domingo is against it, and Brazil and France support neither side.
The delegates also accept that longitude will be measured east and west of the prime meridian up to 180 degrees. They also propose a universal day that begins at midnight Greenwich Mean Time. This does not mean that the conference immediately creates a unified system of time zones. Different countries gradually introduce their own standard times, consistent with the common reference point.
The line today
The historical meridian passes through the transit instrument of the Greenwich Observatory and is marked in place as a line dividing the eastern and western hemispheres. Modern satellite and geodetic systems use a more accurate geocentric reference system. Therefore, the prime meridian shown by GPS is approximately 102 meters east of the historic Greenwich Mean Time line.
This does not change the historical significance of the 1884 decision. It laid the foundation for the common language with which maps, navigation, international timetables, and later global communications began to describe place and time.
Sources: history.com, smithsonianmag.com, nationalgeographic.com