How Greenwich became the world's zero point
In 1884, 25 nations voted to make Greenwich the world’s prime meridian. Here’s why it won, and why the vote never created the time zones we use today.
Image: The prime meridian line in Greenwich, London | stock.adobe.com
‘Spring forward, fall back’. It’s the saying we use to remember which direction the clocks change twice a year. But have you ever stopped to consider the history behind it?
Every autumn, Britain's clocks fall back an hour to Greenwich Mean Time. It’s a small ritual that points to something much bigger. Every map and ship's chart measures east and west from a line drawn through a hilltop in south-east London.
That line got its global job in October 1884, when 41 delegates from 25 nations met in Washington, D.C., and backed Greenwich by 22 votes to one. Yet the conference that gave the world its zero point never gave it the time zones we set our clocks by.
Sky HISTORY examines how Greenwich beat Paris to the prize and why the world's clocks took decades to catch up.
Why did the world need a prime meridian?
Latitude has a natural starting point in the equator. Longitude has none, so for centuries every nation drew its own. Maps measured from national observatories, from St Paul's Cathedral and even from the island of Hierro in the Canaries.
Time was in a worse muddle. Towns set their clocks by the sun, so midday in Bristol arrived ten minutes after midday in London. Then came the railways. In 1840, Isambard Kingdom Brunel's Great Western Railway put its trains on London time, and the railway age George Stephenson had set in motion soon pulled most of Britain onto Greenwich time. It became law in 1880.
America juggled more than 100 local times. On 18th November 1883, its railways switched to standard time zones in a single day. A global fix looked like the next stop.
Why was Greenwich chosen?
Charles II founded the Royal Observatory in 1675 to crack the problem of finding longitude at sea. After two centuries of Greenwich star tables, much of the world's shipping already navigated by its meridian.
In 1879, the railway engineer Sandford Fleming put numbers on it. Some 65% of ships, carrying 72% of world tonnage, worked from Greenwich. Paris trailed on 10%. A geodetic conference in Rome backed Greenwich in 1883, with a hopeful nudge that Britain might return the favour by signing up to the metric system. Weeks after the American railway switch, President Chester Arthur sent out the invitations.
What happened at the International Meridian Conference?
The conference opened in Washington, D.C., on 1st October 1884. Greenwich had the numbers, but France had other ideas. Its leading delegate, the astronomer Jules Janssen, argued that the world's zero should be strictly neutral, belonging to no great power and cutting through neither Europe nor America.
The flaw was practical. A prime meridian has to be measured from a working observatory on solid ground. As the American delegate Commander William Sampson pointed out, Janssen had explained the benefits of a neutral line very fully, but not how anyone would actually find it.
On 13th October, the neutral meridian sank by 21 votes to three. Delegates then backed Greenwich, defined as the line through the centre of the Royal Observatory's transit instrument. The crosshairs of that telescope, the Airy Transit Circle, became zero degrees longitude for the world.
The vote was 22 to one. San Domingo, now the Dominican Republic, voted against, while France and Brazil abstained. The resolutions were formally adopted on 22nd October, with one catch. They were only proposals, and each government had to decide whether to use them.
Did the 1884 conference create time zones?
Plenty of accounts say the conference carved the globe into 24 neat time zones. It did nothing of the sort.
It agreed a ‘universal day’, starting at midnight at Greenwich, for anyone who needed one clock for the whole planet. The resolution added that it should not interfere with local or standard time. When Fleming and another delegate proposed standard time for every nation, others objected that it lay outside the conference's remit, and it never went to a vote.
Time zones grew up piecemeal instead, as country after country chose a standard time a whole number of hours from Greenwich. Even the United States only wrote its zones into law in 1918.
How long did it take the world to fall in line?
Through the 1880s, only Japan acted decisively, setting its clocks nine hours ahead of Greenwich from 1888. Belgium, the Netherlands, Italy and Germany followed in the early 1890s and Spain in 1901.
France held out the hardest. It adopted Greenwich time in 1911, but the law avoided the word ‘Greenwich’. Officially, French clocks ran on Paris mean time, set back by nine minutes and 21 seconds.
The final nudge came from the North Atlantic. At the Titanic inquiry in 1912, it emerged that an ice warning from the French liner La Touraine gave its times by Greenwich but its positions by Paris. Nobody blamed the disaster on the mix-up, but the point was made. France adopted the Greenwich meridian on its nautical documents from 1st January 1914, and by 1929 most major countries were on hourly time zones.
Is Greenwich still the world's zero point?
Here is the twist. In the 1980s, satellite-based coordinate systems needed a prime meridian tied to the centre of the Earth. Today's official line, the IERS Reference Meridian, runs 102.5 metres east of the historic one. That is why visitors straddling the brass strip in the Observatory courtyard never see their phone read exactly zero.
Washington only proposed the line in 1884. It took the world four more decades to agree that time was on Greenwich's side.
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