Why are there 24 hours in a day?

Whyte Ridge

Hey there, time traveller!
This article was published 07/02/2024 (797 days ago), so information in it may no longer be current.

I recently asked my wife to remind me when daylight saving time starts this year (March 10, so you know) and it got me wondering why are there 24 hours in a day. Unlike other measurements and values, such as units of distance, and weight and currency, why is the measurement of time consistent across the world?

So, I thought I’d do some digging and let you know…

The simple answer is that it’s an interesting twist on finger counting. Those of us who grew up before the digital age probably all went through a phase of counting fingers to solve math problems, so there’s logic in the evolution of the decimal system, because we’re using 10 fingers.

More than 3,000 years ago, the Sumerians found they were able to count higher by using the knuckles on their fingers and counting with their thumbs. If you look at the palm of your hand, you’ll see three spaces between the knuckles of each finger. Three times four fingers is 12 for each hand, which equals 24

The ancient Egyptians used base 10 decimal system, but were obviously convinced by the benefits of the base 12 system as historic records show the shift about 3,000 years ago. They used sundials to measure time during the day, which was divided into 10 equal periods, plus another two periods for dawn and dusk before and after the sundial was fully functional. Groups of stars called decans were used to track time during the night, with 12 passing overhead each night. The hours didn’t have a fixed length, however, and it was Greek astronomers in the 2nd century BC who proposed the division of a day into 24 equal hours. They also drew from the Babylonians’ use of the base 60 system for astronomical calculations to further divide the hours into units of 60.

While the Greeks added the additional structure, it wasn’t until the invention of the mechanical clock in 14th century Europe that the system we use today caught on with the general population. Once this was in place, the additional subdivision into minutes appeared near the end of the 16th century. Again, we have the Babylonians to thanks for the 60 seconds, picked up by medieval astronomers.

So now you know.