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Most Googled: why is Greenwich the centre of time?

By El Hunt

Unless you want to bring on an existential crisis, you probably don’t want to devote too much headspace to the concept of time. But have you ever thought about the fact that every other time zone in the world is measured from a single line running through Greenwich? Marking the centre of global time, the line is called the prime meridian – and you’ll find it at the Greenwich Observatory.

‘Meridians are imaginary lines that run from the North Pole to the South Pole,’ explains Emily Akkermans, curator of time at the observatory. ‘They connect all points of the same longitude, which is why they’re important to astronomers and navigators.’

They can also be used to measure time. The sun passes over the prime meridian at around noon each day, but solar time is unreliable; there’s a large margin of error thanks to factors like the earth’s elliptical orbit. However, if you average out all of these sun crossings over an entire year, you end up with a standardised mean (or average) time for noon. Enter: Greenwich Mean Time.

The question is: why does the rest of the world use GMT as a starting point? It goes back to 1884, when the International Meridian Conference took place in Washington DC. ‘Greenwich was selected as the prime meridian of the world because of the observatory’s long-standing reputation for producing good-quality data for navigation,’ says Akkermans. Plus, she points out, ‘Seventy percent of the world’s shipping companies were [already] using charts and data tables based on the Greenwich meridian.’

Further proof that London is the centre of the universe.

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