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.

Find out what longitude is and what makes it so hard to measure.

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

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.

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…

The Royal Observatory Greenwich is famous world-wide as the home of Greenwich Mean Time (GMT). But what is GMT and why is it so important?