Why Your Hour Has 60 Minutes
Every clock in your house runs on a counting system invented about 4,000 years ago in Mesopotamia, and nobody is sure why it was picked. It is a great way to show kids that some numbers are simply better at sharing than others.
- • 60 is the smallest number that divides evenly by 1, 2, 3, 4, 5 and 6, and also by 10, 12, 15, 20 and 30. Ten splits evenly only into halves and fifths.
- • Our words 'minute' and 'second' come from Latin: Ptolemy, around AD 150, called the parts 'partes minutae primae' (first minute) and 'partes minutae secundae' (second minute).
- • The 360 degrees in a circle also come from Babylonian astronomers, but historians argue about why. UCL mathematician Mark Ronan says it comes from an ideal calendar of 12 months of 30 days, not from counting in sixties; others note the Sun moves very nearly 1 degree a day across the sky.
Quick: how many ways can you share 10 sweets fairly? Two people, five each. Five people, two each. Three people? Someone cries.
Now try 60. Two, three, four, five, six, ten, twelve, fifteen, twenty, thirty people. Everyone gets a fair share. 60 is the smallest number you can split evenly between 1, 2, 3, 4, 5 or 6 people.
That may be why the Sumerians liked it. About 4,000 years ago, in Mesopotamia, roughly today's Iraq, they counted in sixties, not tens. The Babylonians kept the habit.
How did it get into your clock? Step one: Babylonian astronomers did their sky sums in sixties. Step two: Greek astronomers copied their methods. Step three: around AD 150, Ptolemy chopped each degree into 60 parts, then each part into 60 again. In Latin: the 'first minute' and the 'second minute'. Step four: astronomers measured time in the same sixties as the sky, so the hour got the same split. Minute, second.
The twist? For centuries, ordinary people ignored minutes. Clocks showed halves and quarters. Clocks showing minutes arrived only about 450 years ago.
And why 60 at all? Nobody knows. Easy sharing? A finger trick: 12 finger sections on one hand, counted with 5 fingers of the other, makes 60. One historian says no one has found 'a really convincing answer'.