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.

Why do clocks go clockwise? © iStock

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Robert is a science writer and visiting professor of science at Aston University.