This Day Has 24 Hours
by
Harold Richman
Why does a day have 24 hours? It seems like an odd number. Well, not exactly odd, but rather unusual. Most of the periods that denote the passing of time have a basis in the movement of the earth around the sun or the moon around the earth. For instance one orbit of the earth around the sun is one year. One orbit of the moon around the earth was considered to be one month. (The word month is derived from the word moon.) One day is one revolution of the earth about its axis. But an hour is entirely a man-made measurement of time.
Why was a day divided into 24 hours instead of some other amount? The explanation is lost in the past but there is a likely theory. We have to go back to Babylonian times when the mathematicians developed a system based on the number six.
We are all familiar with our own decimal system which is based on the number ten, but it is possible to develop a system using another number. The most widely used system in the world today is a system based on the number two. Not many people are aware that all computers operate on such a system because it is all done internally. When you enter numbers into your computer, the decimal number is converted into a binary number and the calculations are done inside the computer using the binary system. Only the results are converted back into the decimal system.
The Babylonian system using six was adopted by the Egyptians and their mathematicians developed many measurements that are still in use today. Whenever you find a measurement that is divisible by six, there is a good possibility that it was originally developed using the sexagesimal system. The fact that the yard has 36 inches and a foot 12 inches may also be based on this system.
The Egyptians used a calendar of 12 months with 30 days each, plus five additional days at the end of the year. The 360 days represented one orbit of the earth around the sun, so they divided the circle into 360 degrees since it was also divisible by six. The tiny circle we now use to denote a degree is thought to be derived from the hieroglyph for the sun which was a circle.
Each degree was divided into 60 minutes and each minute into 60 seconds. Later the hour was divided the same way when clocks were introduced that could keep time with sufficient accuracy.
The day was always considered to be in two parts, daytime and nighttime. The Egyptians were able to divide the day into twelve parts called hours by means of the sun dial, however the nighttime could not be divided as there was no way to measure the passage of time. The daylight period was always divided into twelve segments called hours based on the number six. In winter the hour would be shorter than in summer, because no matter the length of the daylight period, it was always divided into twelve parts. In some Roman documents the writer mentions that the Roman Legion could march "at the rate of twenty miles in five summer hours".
The standard hour was not introduced until mechanical clocks were invented