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  • Greenwich Mean Time

    Visit Greenwich and stand on the Prime Meridian, with a leg in each hemisphere, eastern and western, at the Royal Observatory.

    Nowadays we all take it for granted that we can find out the right time wherever and whenever we are in the world. But it wasn’t always like that. Before the mid 1850s it might be 2.30 in the afternoon where you were and 3.00 in the afternoon ten miles down the road!

    Local time was defined, generally, by the sun and could vary widely across the UK, which was a major headache for the expanding railway industry.

    Passengers didn’t want to find themselves turning up to meet the 11.00 train from Doncaster to Leeds only to find that nobody knew when exactly it might have been 11.00 in Doncaster or when the train would arrive – if it hadn’t arrived already.


    So the standardisation of time began in the 1840s. It was first put into place in December 1847 when the railways switched from local time to Greenwich Mean Time.

    The rest of the country followed and we were all waking up to Greenwich Mean Time by 1865 or so.

    Put simply, Greenwich Mean Time is the annual average of the time when the sun crosses the Prime Meridian at the Royal Observatory, Greenwich, (it’s an average – that’s why it’s called ‘Mean’).

    When you visit Greenwich, you can stand on the Prime Meridian, with a leg in each hemisphere, eastern and western, at the Royal Observatory!


    There’s lots more to see as well – the original building was designed by Christopher Wren and houses the UK’s largest refracting telescope and a fantastic collection of clocks, astronomical instruments and other exciting artefacts.

    Find out more here.