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The Greenwich Prime Meridian (ish)
The Greenwich Prime Meridian (ish)
The Greenwich Prime Meridian (ish)

Last Sunday (October 26), British clocks went back from British Summer Time to Greenwich Mean Time, restoring the whole country to the internationally unified line from which all time (and distance) is measured: Greenwich Mean Time, which is derived from the Greenwich Prime Meridian, running through London. But why London? Why not Istanbul or Indianapolis? Well, let’s see, shall we?

When you’re dividing up a globe into sections so that time works in the same way wherever you are, it’s important to start somewhere. So just as the Equator splits the planet in half widthwise, the Greenwich Prime Meridian does likewise with length, sitting at longitude 0° 0′ 00″ and passing through the right hand side of Great Britain. It passes through Cleethorpes in the North and ends at Lewes in the south. It then slices on down through France, Spain, Algeria, Mali, Burkina Faso and Ghana. Due to the direction that the planet is spinning in, everything to the east is officially in the future, everything to the west is in the past.

Unlike the Equator, which is drawn on the furthest point from the rotational axes of the planet, the prime meridian for international time could have been drawn anywhere—an hour to the east, for example, or five hours to the west—in scientific terms it doesn’t matter at all so long as everyone’s 8 am is near sunrise and everyone’s 8 pm is getting on for sunset, and the gridlines that show location across the planet are the same for everyone. But this hasn’t always been the case.

In the 19th century, time was not uniform. Communities—whether cities or countries—kept their own local time, which meant they created their own prime meridians, starting whenever it seemed right. With the advent of railways (and their timetables) and the telegraph, it became clear that some kind of international accord would need to be reached, time would need to be divided into 24 hour-long segments across the planet so that 6:15 would not suddenly become 6:30 whenever a train arrived at a new station.

In 1884, the International Meridian Conference met in Washington to decide which line would be THE prime meridian for the entire world. It would not be an easy discussion. Delegates from 25 nations had to agree something that would lend one country a certain prestige and status. Washington, London, Berlin and Paris were all hoping to secure the honor, and with no second prize on offer, the conversations got fairly heated.

Britain was in a strong position from the start, nearly three-quarters of the ships on the sea were already navigating with charts that used the Greenwich Prime Meridian, and the U.S. railways were also using a timetable based on Greenwich Mean Time as the standard to ensure the trains ran on time.

But that’s precisely half of the problem; the Greenwich Prime Meridian represents an eternal NOW, travel in one direction and you’re going back in time, the other way takes you forward. But what happens when two people set off in opposite directions from Greenwich and meet on the other side of the world, one adding hours, one taking them away? What time is it then?

That line on which they meet is the International Date Line. One side is half a day ahead of G.M.T. and the other is half a day behind. Therefore it’s important that this does not run through densely populated areas, or you’d be getting your post before it was sent. With the Prime Meridian based in London, the International Date Line can skirt around Alaska and run down the Pacific Ocean without too many problems, apart from the islands it encounters along the way, who have had to decide which side of the dateline they are on. Put the Prime Meridian anywhere else, and you’re splitting whole countries down the middle, using a calendar.

With all these factors at play, the decision was put to a vote and Greenwich won by 22 to one. France and Brazil abstained, and San Domingo was the sole vote against. Not that everyone was happy, as the British Empire was in full blossom at the time and many countries would have preferred a more neutral choice, and even now, 130 years later, some countries shift time to suit their needs on a local level. French time is an hour ahead of British time, for example, because it makes more sense to share a timezone with your landlocked neighbors than the island over the sea.

Having said that, modern technology has also had an effect. It seems GPS maps show that the true Prime Meridian actually lies 100m to the east of the Greenwich Observatory, which plays host to a ceremonial brass strip supposedly running along the line (see image above).

A small crumb of comfort for San Domingo, there.

See more:
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By Fraser McAlpine