Clocks & timekeeping

Royal Observatory Greenwich holds a treasure trove of some of history's most iconic timepieces. Discover the stories behind John Harrison's groundbreaking marine chronometer H1, Charles Shepherd's 'master clock', and the famous Greenwich Time Ball. Plus, find out about the history of timekeeping and its importance to society.


Because the Earth takes a little over 365 days to orbit the Sun, we need to make adjustments to keep the seasons from drifting: leap years and even leap seconds.

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Marking the end of British Summer Time, the clocks go back in October, giving us an extra hour in bed. But why do the clocks change?

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Marking the start of British Summer Time, the clocks 'spring forward' in March, meaning we'll lose an hour's sleep.

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To avoid confusion, the correct way to express 12 o'clock is 12 noon or 12 midnight.


Our collection focuses on three key areas: precision marine timekeeping for navigators, precision timekeeping for astronomers and the broader area of domestic timekeeping and time distribution.

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Why change the clocks, which way should they go, and whose idea was it in the first place? British Summer Time (BST) explained.


How do we calculate the precise moment of sunrise or sunset? And exactly when is twilight?

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For thousands of years, the sundial has told the time and divided the day.


How do you know that your watch, clock or phone is telling exactly the right time? At one time, the only way was to look to the roof of the Observatory.


Next time someone asks you the time, you may enquire if they want to know the atomic, universal, civil, local, solar or sidereal time…