Why are there 24 hours in a day?
2:06pm, 16th September 2003
There are many thing I’m interested in, but one in particular is the number of hours in a day. Well. I’m not obsessed with it or anything, but it’s always made me wonder how on earth we got everyone on earth to agree to split the day into 24 segments. Splitting the year up into 365 days was easy - everybody knew what a day was, and everybody knew what a year was, so they just counted up how many days there were in a year. This happened all over the world, many times, independently in different cultures. When one group of invaders came along to politely ask another group if they would mind, say, changing their religion, the agressors would say “You’ve got a day to think about it before we smash you up”. It’s unlikely these two nations would speak the same language, so this would take a lot of hand waving and pointing at the sun and moon to get across, but across it would nevertheless be gotten. There was no need to go into deep astronomical calculations, because the concept of a day was universal - even newly introduced mortal enemies who didn’t have a word or belief in common, would at least have a measurement in common.
But what about hours? Why 24? Why not 10? Why not 60? Time is not naturally split up into 24 anythings, so the division must be totally artificial. After a bit of googling, I found what I thought was the answer:
At which point Bryan crooked his right thumb to touch the base of his right index finger (please follow along and do it, too), and said, in much the same way as a Sumerian might have, 4,000 years ago… “One.”
He then moved up a notch - see that? Each of your fingers has three distinct segments. I never really noticed that! - and, touching now the middle segment of his right index finger with his right thumb, he said… “Two.”
I think you may sense where this is leading. By the time your right thumb has counted each of the three segments of his neighboring four fingers, you’re up to 12.
Long before people were reading with their lips, one imagines, they were counting with their fingers.
So a day was divided into 12 segments, called hours; and, too, the night.
What a lovely story. It was all the ancient Sumerians’ fault! The ancient Babylonians inherited this quaint practice, and presumably added their own 60-fetish to divide the hours into 60 minutes, and the minutes into 60 seconds. The Babylonian fascination with the number 60 is interesting in itself - so interesting, in fact, that this page suggests the Babylonians were the ones who split up the day, using geometric series:
… base 12 is more efficient than base 10, as base 10 ignores one of the hand configurations available - to wit:
- Open hand
- One finger folded
- Two fingers folded
- Three fingers folded
- Four fingers folded
- All fingers folded
Clams, naturally, have neither the means nor the necessity for such crude mnemonic devices. As well as being fond of twelve (3 x 4) the Babylonians actually used a base sixty notation (3 x 4 x 5) - hence your hours and minutes. The 360 (3 x 4 x 5 x 6) degrees in a complete revolution also stem back to their childlike fondness for these simple geometric series.
So there’s another way of getting the number 12 out of our hands! Even though this explanation comes from the mightily respected “Doctor Clam”, who as it happens, is an actual clam, it shows what we probably suspected: these explanations are total guesswork. How are we supposed to know what number a Babylonian saw when he looked at his hand? They don’t seem to have written that one down.
Back to Google then. This page here has the world “science” in the URL, but the explanation it gives is still a little shaky:
Division of time into days and hours has gradually changed throughout history. In Babylonia the civil day and astronomical day were different. The civil day was divided up into watches [where] the length of a watch [was] not constant but varied with season. There were four watches during the day - 2 during the day, sunrise to midday and midday to sunset, 2 during the night from sunset to midnight and midnight to sunrise. The number of hours probably came from the use of base 6 as a counting system. It made sense to have each watch lasting 6 hours.
We know that the Babylonians used base 60, not base 6, but they did that because it is easily divisible by lots of other numbers, including 6. So the number 6 may have held a little significance. This explanation boils down to the Babylonians being 60-centric. Is that the real reason then? Did the Sumerians’ hands play no part? Perhaps the 12-sectioned hands were a reason for liking base 60 in the first place. Or maybe it was something completely different, as this page suggests. I won’t quote the whole thing, as it’s quite long. Suffice to say that they’ve found an astronomical explanation involving stars, and it was the Egyptians, not the Babylonians. It all seems a little convoluted to me, but apparently “significant stages are documented in monuments and tombs” so maybe there’s some evidence.
But wait! That’s not all! Here we have a slightly different suggestion:
The Babylonians divided the sky into the 12 signs of the Zodiac, and a circle into 360 degrees. They divided the day and night each into 12 hours (although in many time systems the lengths of these varied between summer and winter! Babylon was rather nearer the equator than Liverpool, so they didn’t get too confused with this). The hour was split into 60 minutes and a minute into 60 seconds.
Zodiac signs, eh? We’re back to the unsubstantiated rumours about Babylon.
None of these solve the problem of getting the whole world to use 24 hours. Did Babylonian (or Egyptian) timekeeping spread naturally across the world in the same way Arabic and Hindu mathematical notation did? Did the Babylonians conquer some rival countries, which went on to conquer others, and so on? Are there, in fact, some countries which still don’t use 24 hours? Some isolated island somewhere? Is it just a ‘western’ concept which has been forced onto the world recently by economic might? Come on! Somebody must know! Sorry for the inconclusive ending… how about I have a guess myself?
I reckon that the Babylonians (or somebody else, but if everyone else gets to blame the Babylonians, I will too) started out with the second as the basic unit of time. It’s a nice convenient time interval - if asked to count upwards from one, you’d probably space the numbers about a second apart. Then, using their general love of all things base 60, they must’ve grouped seconds into groups of 60, and called them minutes. Then, they must’ve grouped the minutes into groups of 60, and called them hours. Then when they tried to group the hours into a group of 60, they saw that it spanned more than one day. So instead, they stopped naming time intervals, and simply stated that there were 24 hours in a day. Simple as that! It must be true!
If this really was true, they probably started out with something that wasn’t quite what we know as a second. Perhaps shorter, perhaps longer. They probably went through the above calculation, and found that there were really 24.145 (or whatever) hours in a day, and to round the number down to exactly 24, they reduced the length of the second. Oh, and the human heart beats roughly once every second when resting, so perhaps that was what they started out with… sadly we’ll never know.
1.) I remember a documentary on the Discovery Channel talking about the 12hr day. Back when mechanical clocks were first were being built the numbers on a 24hr clock was too small and buched up to be read efficienlty. Someone suggested a “12hr” face and that gave us 12AM and 12PM.
2.) Just a thought - Since the earths rotation is slowing down over time, will we adjust seconds accordingly? 500years from now will a second actually be 1sec plus .001?
1) Interesting theory…
2) Doubt it. The modern SI second is defined in terms of some property of Caesium atoms which is unlikely to ever change. They’ll probably declare a leap-second to deal with the slowing down of the Earth.
When constructing a sundial, the angle between hours is 15 degrees. 15 degrees is a remarkable easy thing to construct just using a compass. You simply construct an equilateral triangle in the usual way, then split the 60 degree angle twice with the standard construction.
1,000 years from now, when 99.99999% of humanity is off the planet, will we still use the same calendar and clock we use now?
This is an excellent discussion about the basis of our time system. This subject came up during a lunchtime talk today, and I was hoping to find an explanation like this.
The solution may be a mystery but an elegant mystery and there may be something deeper. If one were to look at the face of a clock and go around the clock twice numbering from 1 to 24 a number of things emerge…
-note the patern of prime numbers: 1 & 13; 5 & 17; 7 & 19; 11 & 23
-note the squares 1, 4, 9 & 16…4 and 16 overlay one another and is it possible that the relationship of 1, 4, & 9 represent the placement of the prymids?
-if you continue the sequence there are 5 prime numbers lined up with the 5 position: 5, 17, 29, 41, 53
Coincidence? Right!
i alway thought that the square root of 360 degrees is 24 and the 360 degrees is the earth circling
The square root of 360 is 18.97.
Why 24 hours, ?
I reckon they took the measure, as the time the moon takes, to move through its own diameter which is about half a degree. Anyone can observe this by watching the moon, against a field of stars.
OK, interesting theory..
I thougt I learnt the question I’ve ben asking myself and now I’m going to teach the restof my class it.Thanks and how did you find
the anwer? Thanks again.
Bye!!!!!!!!!!!!!!!
I am just doing a math project so I need scientific information.
More important, I need a site that will give me that information.
Know of any?
According to Wikipedia:
The day was subdivided sexagesimally, that is by 1⁄60, by 1⁄60 of that, by 1⁄60 of that, etc., to at least six places after the sexagesimal point by the Babylonians after 300 BC, but they did not sexagesimally subdivide smaller units of time. They did not use the hour, but did use a double-hour, a time-degree lasting four of our minutes, and a barleycorn lasting 3⅓ of our seconds (the helek of the modern Hebrew calendar). The Egyptians had subdivided daytime and nighttime into twelve hours each since at least 2000 BC, hence their hours varied seasonally. The Hellenistic astronomers Hipparchus (c. 150 BC) and Ptolemy (c. AD 150) subdivided the day sexagesimally and also used a mean hour (1⁄24 day), but did not use distinctly named smaller units of time. Instead they used simple fractions of an hour.
Medieval astronomers first subdivided the hour sexagesimally in 1200[2] into pars minuta prima (first small part, our modern minute), pars minuta secunda (second small part, our modern second), pars minuta tertia (third small part) and so on.
So it seems we owe the division of the day into 24 hours of sixty minutes of sixty seconds to a combination of ancient Babylonian and Egyptian thought, as well as the intervention of medieval astronomers….
I believe Sumerians took the day to be dawn to dusk, and considered the night to be a different thing altogether, so we are talking about daylight hours. So the question is really “why are there twelve hours in daylight?”(at the equinoxes) The answer is that they picked 12 because they saw twelve months in a year (approx 12 moons). And they liked to have “as above so below” i.e. they liked to see small patterns reflect grand patterns. Hence they wanted the daylight period to be divided like a year so they divided daylight by 12.
i have wondered about this too. ive wondered, since there are not really 24 hours in a day, how much time have we ‘lost’ or ‘gained’ over all these years?? wat year is it really?!
it was such nice explanation but there are certain assumpttion
According to Wikipedia: the number of African elephants has tripled in the past fee years. Never listen to Wikipedia. At best, it’s just Google scraping. At worst, it’s propaganda by governments and corporations. Most often, it’s poorly written crap in a nice package.
That wasn’t me.
Obviously. lol
This Is Ridiculous
Dimensional/Geometric Reason Why Ancient Egypt Chose 24H/Day:
http://youtube.com/watch?v=RhNmlQqQOTw
It probably all goes back to a mix of superstition and geometry. 12 can be divided by the whole numbers 12,1,6,2,4 and 3. 10 can only be divided by 10,1,5 and 2. This makes 12 the more convenient number for thinking in segments. Add to this your zodiacs, gods, apostles and whatnot and Bob’s your uncle. In Japan they used to give the hours names, for example “I’ll meet you by the well at the hour of the Ox,” which possibly came from Chinese zodiac or equivalent. Interesting question though.
Chris is getting closer to the answer. Our earliest ancestors only had three things to determine time. Sun, moon and stars. Many civilizations attribute gods to these entities. The Sunrise and Sunset would be half of this period of time. At night, they would watch the stars. They noticed that after about 360 times that the sun went up and went back down that the stars were in the same place in the sky. They would have also noticed that the moon would appear full 12 times, every 28 1/2 days. Thus, a system is created that is shown in our modern calendar 365 days (Sun/star ratio) 12 months(moon). Don’t you also suppose that they would honor the Sun, Moon and stars in the way they calculate time within the day? 60 seconds X 60 minutes = 3600 Sun/Star ratio. Two subsets for day and night (Sun and Moon), and then a way to honor the moon cycles (12) hours. E-mail me if you have any further questions about this.