Time is Relative or Why 24 hours in a day and not 360?

My mind was wandering the other day, as it often does when I am supposed to be doing something, and I realized that I know where the metric system comes from (based on the size of the earth!) and roughly where the “English” units of measurement came from (http://www.factmonster.com/ipka/A0769529.html)

I was familiar with the origins of  Celsius/Centigrade (based on the freezing and boiling points of water at one standard atmosphere) and Kelvin (based on the temperature at which molecular movement ceases) came from. ( I had to look up the Fahrenheit scale. He based on on his own body temperature! No wonder I didn’t know it. I probably just forgot. You can read about all three at http://www.school-for-champions.com/science/temperature_scales.htm)

I knew where the Dewy-Decimal system came from (invented by Dewy to make life easier). I understand astronomical units and light years. I get the four seasons and a year (months are a bit arbitrary though).

But I didn’t understand why there were 24 hours in a day and 60 minutes in an hour and 60 seconds in a minute.  Why not 360 seconds in a minute? 360 minutes in an hour? Wait! Why is a circle divided into 360 degrees? This is one of the best answers I found: http://mathforum.org/library/drmath/view/58395.html

The ancient Babylonians’ method of dividing up a circle gave it to us! Well, I suspected that it was related to the circle because of nomenclature, but it still didn’t make any sense to me.

Probably because over centuries, other peoples muddled with things to give us the time scale we are used to now, but it is all still based on the original Babylonian base 60 number system. What’s a base 60 number system? (careful, that one can hurt your head). Well, we use a base 10 number system. We go numbers 0 through 9, and then start over into the next column with 10. Computers use a base 2 (Binary) number system. Counting 0 and 1 and then starting over into the next column. This is a great place to see how.  So base 60 counts to 59 BEFORE moving into the next column.

So! The Babylonians divided the day they same way they divided a circle. It makes a circular kind of sense. But they did divide the day up into 360 parts, lasting 4 minutes each. They called them “ush” and they are the same as the degrees in a circle. They were measuring time astronomically, basing it upon the rotation of the earth. A great place to see what they were doing is at  http://www.jeremychapman.info/cms/the-babylonians-and-the-mayans-an-archeoastonomical-overview-of-two-major-cultures

But that isn’t what we use. It must have been impractical for the average person to try to keep track of 360 hours a day.

So it is thought that the 24 hours come from the Egyptians, who counted in base 12. They divided the day into two parts, day and night, and then each part into twelve. Keeping track of the passage of time with sundials was standard, and problematic. Hours during the summer day were longer than the winter day, and vice versa for nights. So astronomers came up with equinoctial hours, hours based on the length of the day at the equinox.

And there we have it, the 24 hour day. But most people used sundials for a long time after equinoctial hours were devised. It was hard until the clock was invented. But that is a whole ‘nother story!


Further reading on the subject where others have attempted to collect information on this subject: