How was the length of a second first calculated?

Asked by: Rory Eaton, Brighton

Ancient civilisations like the Babylonians focused on the major time units of years, days and hours, whose relative lengths they determined using astronomical observations. But the invention of the first practical clocks in medieval times allowed finer division. These were named in Latin pars minuta prima – ‘the first very small part’, now called the minute; and pars minuta secunda – ‘the second very small part’, now called the second.

Following the tradition set by the Babylonians, these divisions were expressed using the sexagesimal system, a form of counting based on units of 60. Using this, the length of a second became a sixtieth of a sixtieth of an hour, leading to its definition as 1/3600th of an hour.

Read more:

• Do dogs have a concept of time?
• Why do clocks go clockwise?

Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun facts.