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Why does a day have 24 hours?

by Mya Kagan (whyzz writer) >> more about the author

Why does a day have 24 hours?
 
Hour Power!  

For thousands of years people all over the world have been using terms and divisions like “day,“ “night,“ “hour,“ “minute,“ “yesterday,“ and “tomorrow” to talk about lengths of time. The idea of “a day” – from when the sun rises to when it sets – has always been a pretty basic way of thinking about time. (Especially before there was electricity and “day” and “night” were even more distinguishable!) Within “a day” people usually break down time into units we call hours!

Nobody knows the exact reason why it was decided to measure out an hour so that 24 of them would fit into a day, but we do know the practice goes all the way back to the Ancient Egyptians! One reason they chose to divide a day into a 12-hour day and a 12-hour night is probably because they used to count in a system based on 12. (We now count in a system based on 10.) It’s also possible they chose 12 because that was the number of moon cycles (months!) in a year. The Egyptians made and used sundials to tell time (there were no clocks yet!) and by looking at the remains of these creations, we can trace what is believed to be the origins of our 24-hour day back to them!




Here comes the sun!

Before there were clocks, people used the position of the sun in the sky to know what time of day it was!

Try this experiment:

Go outside in the morning on a sunny day, and take a look at the position of the sun. Try especially to notice where it is in relation to something nearby that won't move -- like a tree or a street sign. Draw a picture of where you see the sun.

Go outside again in the middle of the day, maybe right after lunch. Is the sun in a different place now? Look for the object you picked out earlier in the day -- is the sun in a different place in comparison to the object? Draw the midday sun's position on your picture from that morning.

Do the same thing again in the evening, and draw the sun's position at the end of the day on your picture, too.

What do you notice? Do you think that if you went outside again the next day, you'd be able to know what time it was because of the position of the sun??