Why we have 24 hours, 60 minutes and 60 seconds

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

10 January 2021

Last week we ended at this question: why are there 24 hours in a day? Why not a nice round number like 10 or 20? One story has it that ancient Egyptians had divided the daylight period into ten segments. They then added one segment at dawn and at dusk to account for the twilight periods when it is neither day nor night. 10 + 1 + 1 = 12.

With daytime divided this way, it made sense to do likewise to night time. However, since the twilight has already been accounted for, this would give ten segments of darkness, thus a total of 12 + 10 = 22 segments in a day. Therefore, that story does not really add up.

Another explanation says that the 24 hours was developed by the Babylonians of ancient Iraq. In this civilization, counting was done in groups of 12. This was convenient since it is the number of finger segments in one hand (excluding the thumb).

If you hold out your hand, you will find that you can touch (and count) the segments of the other fingers using the thumb of the same hand. Try it! Since a person has two hands, the total is 24.

Thus, for Babylonians, it was natural to divide the day and the night into 12 segments each. I imagine that they designated the right hand to the day time and the left to the night time. But the story doesn’t end there…

Suppose you are doing some arithmetic using this Babylonian method. You can count 12 things with the finger segments of one hand. For larger numbers, you need to keep track of how many groups of 12s you have counted. The five fingers of your other hand come in handy!

You can fold one of these fingers each time you complete a count of 12 on the segments of the other hand. Therefore, you can now count up to 60 (= 12 x 5) using both your hands. Using this counting method, the Babylonians had developed a number system that worked in base 60.

Consequently, when they needed to divide the 24 segments (hours) of a day into smaller fractions, the number 60 came naturally to them. This is how we ended up with 60 minutes in one hour…and 60 seconds in one minute.