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.


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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Who was John Harrison, and how did his clocks help to solve the problem of finding longitude at sea?

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


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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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…

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While days and years are (fairly) neat astronomical events, what explains months, weeks, hours and minutes?