General Question

jackm's avatar

Why is the day split into two 12 hour periods?

Asked by jackm (6198points) February 9th, 2010

Why do we split up the day at noon, and not just use the military 24 hour clock?

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35 Answers

erichw1504's avatar

I don’t know, but I would be all-for adopting the 24 hour military way of reading the time of the day. It eliminates the use of AM and PM, which can confuse people when used wrong.

jackm's avatar

@grumpyfish No one in the question answered this question.

robmandu's avatar

Here’s a run down of several suggested explanations: http://james.lab6.com/2003/09/16/24hours/.

Base 6, base 12, base 60, Sumerians, Babylonians, Zodiac, oh my!

JLeslie's avatar

I’m guessing clock makers had a hard time fitting 24 hours and being able to read it easily. Just a guess.

Most of the world does use the 24 hour clock I think. America tends to stick with the old way of doing things, like not switching to metric.

buckyboy28's avatar

My guess would be that the U.S. really likes to use arbitrary systems. I would be for adopting Celsius, the metric system, and the 24 hour clock. It won’t happen, but one can dream.

jackm's avatar

@Lightlyseared
Thanks, I read that earlier, but it never says why we use the 12 hour period, just when it came about and who uses it.

buckyboy28's avatar

@JLeslie if I buy you a coke can I be off the hook?

JLeslie's avatar

@buckyboy28 You are not on a hook, just means we said the same things at the same time. But I do love coke.

AstroChuck's avatar

I suppose ringing the church bells twenty-four times was just too much. Plus it might be easier to miss hearing a ring if the bells ring more than twelve times and that’s the source you use to tell what hour it is. Splitting the day in two halves would make pretty good sense.

JLeslie's avatar

@AstroChuck Good point. My sister used to call in noise complaints about the church down the street.

njnyjobs's avatar

The 24 hour day and 60 minute hour originated with the Babylonians, who based their calendar on the earlier Sumerian and, perhaps, Egyptian calendars. The Encyclopedia Britannica has a number of good articles on this subject, and there is a wonderful chapter by Daniel J. Boorstin in “The Discoverers”. As Boorstin explains, the history of timekeeping is itself lost in time.

The origin of a counting system based on 60 is related to astronomical cycles in the earth-moon-sun system. The earth takes about 360 days to orbit the sun, and over the course of a year the moon goes through about 12 cycles. Our life today is not very well keyed to these astronomical periods, but following and understanding the flow of the seasons was a great deal more important in earlier societies.

The Sumerians were probably the first to develop a calendar based entirely on the phases of the moon. The Babylonians refined this idea to form a calendar of which several details survive in our “modern” calendar. A Babylonian month began on the first day of a new moon. There are slightly more than 12 Babylonian months in a year (about 12.37 to be more precise). [Every two or three years, the royal astronomers would insert an extra full month into the calendar…so that the calendar based on the moon’s cycles would stay in better sync with the year]-

From the fact that there are about 12 lunar months in a solar year, the Babylonians decided that the number 12 is the logical number by which time should be further divided. -From about 300BC, the Babylonians used a hemispherical sundial-type device to keep time during the day. The shadow cast by a thin rod would travel past 12 equally spaced marks on the inside of a hemisphere. The time it took for the shadow to pass from one mark to the next was ONE HOUR. Thus there were 12 hours during daylight. The night time was also divided into 12 parts, as timed most likely by water clocks…the other type of Babylonian clock. (Note that this Babylonian system yields hours which are shorter during winter.when the days are shorter.and longer in summer. As a result, in Babylon, in modern-day Iraq, the daylight hours in mid-winter were only ⅔ as long as the mid-winter night time hours with the opposite situation occurring in mid-summer.

The invention of accurate mechanical clocks at the end of the 13th century finally made the variable-length hour less useful than the modern hour of unchanging duration.-The Babylonians divided the hour into 60 minutes (60 = 5×12….that preferred number 12 appears again).

gambitking's avatar

simple, short answer: because of the length of time it takes for our beloved planet to run once around the sun

grumpyfish's avatar

@gambitking You’re aware that 24 hours = the time it takes the sun to orbit the very stationary earth, YES?

CyanoticWasp's avatar

Along the same lines, I’m wondering if maybe it’s time (so to speak) to go to a different “week” measure. Who says we can only have seven days in a week? Why not six, eight, nine, ten, or some other number?

Personally, when I worked a workweek of four 10-hour days and had three days off every week, I had the best time of my life. I got to do grocery shopping, laundry, banking and stuff like that (back when we actually had to “go to the bank” weekly) on Fridays—with no crowds—and I had the entire weekend to kick back, go to the beach, and relax.

I would love to work four days on and four days off, or work my normal 5-day week and have three days off every weekend.

Let’s break the cycle of 7-day weeks, I say.

grumpyfish's avatar

Interestingly, the Babylonians divided the hours into minutes (1/60th of an hour), seconds (the second division or 1/60th of a minute), thirds (1/60th of a second), and fourths (1/60th of a 1/60th of a second, 0.2778 ms) They didn’t have timekeeping devices that worked this accurately, but were able to calculate astronomical movements that precisely.

UScitizen's avatar

It isn’t. The day is divided into 24 equal parts. Each part is called one hour.

njnyjobs's avatar

@CyanoticWasp your 4-day 10-hour work week that you find extra-ordinary will no longer be if everyone shared that schedule . . . so be thankful that you get to work in such a sked and leave the system the way its is for now.

erichw1504's avatar

@UScitizen No, the day is divided into 1440 parts. Each part is called one minute.

JLeslie's avatar

@gambitking Come on now. The earth to spin once around on its’ axis.

erichw1504's avatar

@grumpyfish You’re aware that 365 days = the time it takes Earth to orbit around the Sun?

JLeslie's avatar

@erichw1504 I am assuming @grumpyfish was teasing @gambitking. Do you think they both are unaware why the legnth of the day is 24 hours and the time it takes the earth to go around the sun?

erichw1504's avatar

@JLeslie And I was double teasing. Who knows.

njnyjobs's avatar

Ok, the question asked: Why do we split up the day at noon, and not just use the military 24 hour clock?

Answer: WE didn’t split the day at noon, our ancestors did… and the military 24 hour clock was for military use, the rest of us are civilians….we can be forgiven for mistaking an AM appointment with a PM. However, imagine you were undertaking a military operation and you were scheduled to strike a target at six o-clock (AM) but understood it to be six o’clock (PM), you are either ahead of schedule or behind schedule, the operation would be a failure….

But ironically, military personnel also use analog watches that have 12-hour rotations. So, what exactly is the point of having a 24-hour timepiece?

robmandu's avatar

Many Europeans refer to the 24-hour clock when telling time. For example, they typically refer to 4 p.m. as 16:00 in everyday civilian use.

JLeslie's avatar

@njnyjobs Even civilians can screw up an appointment time. Still most of the world uses the 24 hour clock, or uses both. Most Americans can’t even figure out military time, which is ridiculous. Not to mention how many Americans don’t know whether 12:00 midnight is 12am or pm. All of this just continues my rant about our inability to accept metric, and we are one of the few countries that puts the month first than then the day then the year when writing the date, maybe the only one? Not sure about that. Plus, with digital time pieces it is easy to have military time on your wrist if you want it.

njnyjobs's avatar

yeah yeah yeah…. all this talk about european this and european that, how about moving to europe and get your fix of metric and 24-hour time . . . you happy now?!?!? :p

Most Americans can’t even figure out miltary time, don’t know whether midnight is AM or PM??? is that a fact . . . Do they actually have 24-hour watches in analog form?

robmandu's avatar

@njnyjobs, ask and ye shall receive.

njnyjobs's avatar

@robmandu good find . . . would you wear one?

grumpyfish's avatar

@erichw1504 ~Seasons are caused by the yearly variation in the Jet stream (on a shorter, but similar cycle to the sunspot cycle) and icing patterns—as the ice pushes into lower latitudes due to a flatter jet stream, it causes winter, etc.~ (Yes, I was teasing @gambitking‘s typo, sorry if it wasn’t obvious)

JLeslie's avatar

@njnyjobs Most is a strong word I would agree, but I have met more than one person who thinks 12:00pm is midnight. I am not saying Americans are too stupid to figue out military time, but they are not exposed to it very often and I swear when I have tried to tell them an easy way to figure it out they are lost. They don’t understand base 12, or bases at all, or they would be in favor of metric because it is way easier to move a decimal than to multiply or divide by 8, 12, or 16. Of course converting to it would be complex for business and industry, but it is simpler to work with metric, and generally our sciences already use it.

Here is a link about the 24 hour clock and who uses it. http://en.wikipedia.org/wiki/12-hour_clock About a quarter of the way down is a list of countries who basically use the 12 hour clock solely. The list is not that long.

JLeslie's avatar

Oh, and I just read further down on that link and it discusses Criticisms and Practical Problems of the 12 hour clock and complications that can happen especially when talking with people who primarily grew up with the 24 hour clock (which I would guess you don’t give a damn about whether you can communicate well with them or not) and below that Confusion at Noon and Midnight, that you might be interested in.

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