Eli5 why is time measured in base 12 and 60 when we generally use base 10 for everything else?
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The American non-metric systems frequently use numbering systems that aren’t base 10. Cooking comes to mind. Cups and ounces and gallons are often binary, or fractional. 3 teaspoons to a tablespoon, 3 tablespoons to a quarter cup, 2 cups to a pint, 8 pints in a gallon. 16 ounces in a pound. All of that stuff, and not a single 10 in sight.
Systems, including time, that *don’t* use base 10 usually evolved from a system where it’s easy to *divide* into equal parts. 12 is great for this because you can cut it in half not once, but twice, and you can cut the whole 12, *or* half of the 12 into halves *or thirds.* In the cooking example I used, pretty much everything except for the tablespoons and teaspoons is double or half, or some form of it. 8 pints in a gallon, as 8 can be halved 3 times. Also easy to note that a **lot** of foods and liquids in the home weigh *about* the same so that the old adage “A pint’s a pound the world around” usually holds true enough. Two cups (a pint) of most common ingredients is going to weigh about a pound.
**TLDR** 12 divides very easily, which makes it convenient for domestic use where a very fine degree of accuracy isn’t required, but ease of use is.
12, 60, and 360 have more integer divisors than their counterparts 10, 100, and 1000 which makes it much easier to divide things up. This holds for both time and angles (navigation). [Decimal time](https://en.wikipedia.org/wiki/Decimal_time) has been tried but never caught on. Similarly [milliradians](https://en.wikipedia.org/wiki/Milliradian) have been used for angles, but there are several competing standards and for most people and most uses, degrees are just simpler.
12: 1, 2, 3, 4, 6, 12
60: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60
360: 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36, 40, 45, 60, 72, 90, 120, 180, 360
vs
10: 1, 2, 5, 10
100: 1, 2, 4, 5, 10, 20, 25, 50, 100
1000: 1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 125, 200, 250, 500, 1000
Superstition influenced timekeeping’s development. Some people were averse to the idea of a 13th hour or any time on a clock that might read 6:66. Military minds were not so dumb and have a 24 hour clock.
It’s based on the number system of the babylonians. They did everything in base 12, because it was a holy number, and also because they didn’t count fingers, they counted finger-joints but not on the thumb, so one hand could count to 12
The 60 minutes came later (roman times) but were chosen because it’s a multiple of 12
The metric system was invented in the 1790’s, and we still have many things that follow older traditional units of measurement or units of counting. Donuts are still sold by the dozen. Many people in the UK refer to weight by stone instead of pounds or kg.
Base 12 has been in use for thousands of years, we’ll never now for sure why since it predates recorded history. Base 12 is easy to count on your fingers. Using your thumb as a pointer and counter your finger segments allows easy counting to 12 on on hand, and 12 to the power of 2 lets you easily count up to a gross with both hands.
12 is easier to make division, it divides easily into both quarters and thirds without requiring fractions or decimals (neither fractions nor decimals would be invented for quite some time)
In today’s world, the most widely used numeral system is decimal (base 10), a system that probably originated because it made it easy for humans to count using their fingers. The civilizations that first divided the day into smaller parts, however, used different numeral systems, specifically duodecimal (base 12) and sexagesimal (base 60).
Thanks to documented evidence of the Egyptians’ use of sundials, most historians credit them with being the first civilization to divide the day into smaller parts. The first sundials were simply stakes placed in the ground that indicated time by the length and direction of the resulting shadow. As early as 1500 B.C., the Egyptians had developed a more advanced sundial. A T-shaped bar placed in the ground, this instrument was calibrated to divide the interval between sunrise and sunset into 12 parts.
This division reflected Egypt’s use of the duodecimal system–the importance of the number 12 is typically attributed either to the fact that it equals the number of lunar cycles in a year or the number of finger joints on each hand (three in each of the four fingers, excluding the thumb), making it possible to count to 12 with the thumb. The next-generation sundial likely formed the first representation of what we now call the hour. Although the hours within a given day were approximately equal, their lengths varied during the year, with summer hours being much longer than winter hours.
Without artificial light, humans of this time period regarded sunlit and dark periods as two opposing realms rather than as part of the same day. Without the aid of sundials, dividing the dark interval between sunset and sunrise was more complex than dividing the sunlit period. During the era when sundials were first used, however, Egyptian astronomers also first observed a set of 36 stars that divided the circle of the heavens into equal parts. The passage of night could be marked by the appearance of 18 of these stars, three of which were assigned to each of the two twilight periods when the stars were difficult to view. The period of total darkness was marked by the remaining 12 stars, again resulting in 12 divisions of night (another nod to the duodecimal system). During the New Kingdom (1550 to 1070 B.C.), this measuring system was simplified to use a set of 24 stars, 12 of which marked the passage of the night. The clepsydra, or water clock, was also used to record time during the night, and was perhaps the most accurate timekeeping device of the ancient world.
The timepiece–a specimen of which, found at the Temple of Ammon in Karnak, dated back to 1400 B.C.–was a vessel with slanted interior surfaces to allow for decreasing water pressure, inscribed with scales that marked the division of the night into 12 parts during various months.
Once both the light and dark hours were divided into 12 parts, the concept of a 24-hour day was in place. The concept of fixed-length hours, however, did not originate until the Hellenistic period, when Greek astronomers began using such a system for their theoretical calculations. Hipparchus, whose work primarily took place between 147 and 127 B.C., proposed dividing the day into 24 equinoctial hours, based on the 12 hours of daylight and 12 hours of darkness observed on equinox days. Despite this suggestion, laypeople continued to use seasonally varying hours for many centuries. (Hours of fixed length became commonplace only after mechanical clocks first appeared in Europe during the 14th century.)
Hipparchus and other Greek astronomers employed astronomical techniques that were previously developed by the Babylonians, who resided in Mesopotamia. The Babylonians made astronomical calculations in the sexagesimal (base 60) system they inherited from the Sumerians, who developed it around 2000 B.C. Although it is unknown why 60 was chosen, it is notably convenient for expressing fractions, since 60 is the smallest number divisible by the first six counting numbers as well as by 10, 12, 15, 20 and 30.
Although it is no longer used for general computation, the sexagesimal system is still used to measure angles, geographic coordinates and time. In fact, both the circular face of a clock and the sphere of a globe owe their divisions to a 4,000-year-old numeric system of the Babylonians.
Source:
https://www.scientificamerican.com/article/experts-time-division-days-hours-minutes/#:~:text=This%20division%20reflected%20Egypt’s%20use,making%20it%20possible%20to%20count
Rule 2.
Better to r/askhistorians about this.
Our timekeeping and calendar practtices appear to have originated in Sumer about 5,000 to 6,000 years ago. The Sumerians used a base 60 number system (ours is base 10) so their timekeeping and calendar practices stuck.
The choice was made on simple astronomic facts: The earth circles the sun in roughly 360 days, a moon phase takes roughly 30 days. Building a calendar on these, you easily arrive at a base 12 system, since 360/30=12. The Babylonians did that already in ancient times.
Then, if you simply apply the same unit for the earth’s rotation, you have a scale for a sunclock that nicely fits your calendar. Ok, it’s 24 hours but you only get about 12 hours of sunlight.
Quite pragmatic, actually.
Fun fact: The french revolution tried to use base10 for everything. There were also a decimal calendar and a decimal clock! But they didn’t catch on.
The reason for this is called path dependency. Many processes and conventions are based on the base12 system. Changing them would introduce costs that would exceed the convenience of a base10 system (change calculation models, convince stubborn people, …). Sometimes the better solution is too hard to establish. Also, you never know if it really is better before you roll it out.
A similar discussion is that about the Dvorak and other keyboard layouts.
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