3 min
Why is an hour 60 minutes long, and a day 24 hours?
Twenty-four hours and sixty minutes came from two different ancient civilisations — Egypt's twelve star-groups and Babylon's base-60 counting. A quick bean experiment shows why 60 was so handy.
Answer
What you see
Look at a clock: twelve numbers around the face, sixty little ticks in one hour, and two trips around the face in one day. Those numbers feel as natural as sunrise — but they came from two ancient civilisations that never met.
Where the 24 came from: Egypt's night sky
Every year the Nile flooded, and Egyptian farmers watched for Sirius, the bright star that rises just before dawn to announce the flood. At night they noticed that the stars took turns: twelve groups of stars rose one after another over the horizon. So they cut the night into twelve parts. The day could be cut the same way — twelve more parts. Twelve plus twelve makes twenty-four.
Back then an "hour" was a seasonal hour: long in summer, short in winter. It was the Greek astronomer Hipparchus, in the Hellenistic period, who joined day and night together and cut the whole thing into 24 equal hours. That is the hour we still use today.
Where the 60 came from: Babylon's counting board
The base-60 system began with the Sumerians around 3000 BC and was passed on to the Babylonians. Why did they love 60? Because 60 splits neatly almost any way you like: it is the smallest number that can be divided exactly by 1, 2, 3, 4, 5 and 6, and it has twelve divisors.
Share an hour between 2, 3, 4, 5 or 6 people, and everyone gets a whole number of minutes — no leftovers. Try it with 10 and it breaks at once: 10 shared between 3 people gives 3.33. Greek astronomers picked up base-60 for angles and star tables, and later the same habit was carried over to time — giving us 60 minutes and 60 seconds.
Try it yourself: prove that 60 is handy
Get 60 dried beans (or coins) and 10 more.
- Share the 60 beans between 2, 3, 4, 5 and 6 people — it comes out even every time, with none left over.
- Do the same with the 10 beans — 3 people leaves 1 bean over, 4 people leaves 2.
Then count on your own hand: point with your thumb at the joints of your other four fingers. Three joints each — that is exactly 12. Some people guess this is why ancient people liked 12 and 60 (one hand counts to 12, the other hand counts how many rounds, and five rounds make 60). It is only a guess, though — nobody knows for sure.
One more surprise: a day is not one spin of the Earth
The Earth only needs 23 hours, 56 minutes and 4 seconds to turn back to the same angle. That is called a sidereal day. Our 24-hour day is a mean solar day: while the Earth spins, it is also travelling around the Sun, so it must turn about one extra degree before the Sun is overhead again. Those extra 4 minutes are the price of chasing the Sun.
Michael's Thought
So my watch was built by Egyptians and Babylonians together — and they almost certainly never met.
Sources
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