It seems trivial to ask, but why is the day divided into 24 hourseach hour is made up of 60 minutes and every minute from 60 seconds (except for the occasional 61-second minute)? In the metric system, physical quantities (for example mass and length) are measured according to multiples of 10, while time is an exception and is measured with apparently strange units of measurement: seconds, minutes, hours… How did we arrive at this scanning of time?
The answer is to be found in antiquity, starting from ancient Egyptians in 2000 BC, who adopted the numbering duodecimaland it has to do with the Moon, but also with the mathematical properties of the number 12.
Because the day is divided into 24 hours
The origin of division of the day into 24 equal parts it is to be found not so much in the number 24, but in 12. This number has always had a certain importance, so much so that it is also one of the few quantities to have its own name: the dozen. Already the ancient Egyptians around 2000 BC had begun to use the duodecimal numbering (i.e. in base 12) dividing the daytime hours into 12 equal parts, and so also those of the night. Hence comes the practice of dividing the day into 24 hours. But why? The reasons behind this choice are both astronomical, mathematical and practical.
That lasted about a year 365 days it was already observed in ancient times starting from the apparent motion of the Sun. But not only that: in the same period of time it was possible to count approximately 12 cycles of the moon phases. Already in Sumerian times this determined the division of the year into 12 months.
The fortuitous coincidence is that the number 12 has different mathematical properties. One of them is that It has numerous dividers: 1, 2, 3, 4, 6, 12. This fact makes it easily divisiblethat is, divisible into equal parts of different sizes. Another possible reason why the 12 has historically been useful on a practical level is that through the phalanges of the fingers you can count up to 12 using only one hand. Considering the thumb as a counter, in fact, it is possible to assign values from 1 to 12 to the phalanges of the index, middle, ring and little fingers.
Using two hands, then, it is possible to even reach up to 60: one hand is used to count up to 12, while the other indicates how many times 12 should be counted (in fact 12 · 5 = 60). Here are some elements that can help explain why 12 was chosen as the quantity to divide the duration of day and night.
Because the hours are divided into 60 minutes and the minutes into 60 seconds
We therefore arrive at the second question: why does each hour last 60 minutes and not 50 or 100? The answer also lies here in the properties of a number, this time – precisely – 60. Already i Sumerians in 2000 BC they had introduced a system of sexagesimal numbering (i.e. base 60) which included 60 different symbols. Of course, it may seem bizarre to us and much more complex than our use of the decimal system, which only has 10 symbols.
The number 60, as well as 12, possesses many dividers (ironically, there are 12). This makes 60 an easily divisible number, and for this reason an hour made up of 60 minutes is to be considered particularly practical: there are in fact many ways to divide 60 into equal parts, which makes it preferable to a division into hundredths. For example, I can easily take 1/6 of an hour divided into sixtieths (that’s 10 minutes), but I couldn’t do this if the hour were divided into hundredths (I would get a non-integer number of “minutes”).
