# What was the rationale in designating midnight as 12AM? **URL:** \ **Category:** Factual Questions\ **Created:** [May 13, 2017, 2:37pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533 "2017-05-13T14:37:27Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [May 14, 2017, 4:38am UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/41 "2017-05-14T04:38:08Z")
> [@Riemann](#): > > When you’re ten minutes into the morning, the time should logically be zero hours and 10 minutes, not 1 hour and ten minutes. Well, logic is relative here. It depends whether you are into zero-indexing or not. (I happen to use the 24 hour clock for my personal use, so 0 indexing is fine with me.) But, historically, it seems folks of yonder day liked to start at 1. Years start at one. Months start at one. Days start at one. Why not hours? (Of course, then you’d run into the problem of minutes and seconds do start at zero.) But what’s illogical about starting at one? Think of it as “the first hour” as opposed to “one hour past the meridian.” I see no reason why logic couldn’t have gone that way. Once again, not that I personally prefer that logic, I like my zero hours, but there’s no reason to me why starting with one is any less logical if we don’t start counting days or months or years at 0, but instead 1. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [May 14, 2017, 4:41am UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/42 "2017-05-14T04:41:44Z")
> [@GinoC](#): > > In military operational writing the problem is avoided by never using 0000 or 2400. Only 0001 or 2359 are permitted. This is just silly. I’ve worked for a government agency that had this convention and it was daft. 0000 is the start of the day and 2400 (if ever needed) is the end of the day, there is no need to try and avoid those particular numbers. In civil aviation weather reports and operational notices times are often abbreviated to hours with no minutes. It is very clearly understood that 00 hour on the 24th of May is midnight between the 23rd and 24th while 24 hour is midnight between the 24th and 25th. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [May 14, 2017, 4:43am UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/43 "2017-05-14T04:43:18Z")
> [@Ann\_Hedonia](#): > > Our crew call sheets ALWAYS gave the call time as (Day of Week, 12:01AM). It kept people from showing up on the wrong day. This is another thing I like about the 24 hour clock. What day does midnight belong to? With the 24 hour clock, you can say Monday 24:00, or Tuesday 0:00 (although I think I only see the former generally on train schedules) and it should be clear which midnight you’re referring to, without having to resort to “cheating” the time by adding a minute to it. ---
**Author:** ![Nava](https://avatars.discourse-cdn.com/v4/letter/n/da6949/32.png) [@Nava](https://boards.straightdope.com/u/Nava)\ **Post date:** [May 14, 2017, 7:08am UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/44 "2017-05-14T07:08:00Z")
> [@Acsenray](#): > > Here’s a more interesting question. To me, Tuesday night lasts until dawn in Wednesday morning. Wednesday morning doesn’t start until dawn. How is that a question, and how is it unusual? To designate the same night in reference to Wednesday we even have a special word (which also refers to Tuesday itself): eve. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [May 14, 2017, 10:05am UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/45 "2017-05-14T10:05:29Z")
Comes up for those of us on night shift. Typical conversation at say 2am: “You working tonight?” “Well, yeah, obviously. I’m here now with you.” “No I mean tonight, like after we’ve gone home and slept for the day.” “Oh, you mean tomorrow night! Yeah I’m working.” ---
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [May 14, 2017, 11:31am UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/46 "2017-05-14T11:31:44Z")
> [@GinoC](#): > > In military operational writing the problem is avoided by never using 0000 or 2400. Only 0001 or 2359 are permitted. —What time is it, Mr. Fox? —2400! RAAAAHHR! —That is invalid, soldier. You lose. ---
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [May 14, 2017, 11:34am UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/47 "2017-05-14T11:34:14Z")
> [@GinoC](#): > > In military operational writing the problem is avoided by never using 0000 or 2400. Only 0001 or 2359 are permitted. —What time is it, Mr. Fox? —2400! RAAAAAHHHR! —That is invalid, soldier. You lose this round. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 14, 2017, 12:09pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/48 "2017-05-14T12:09:33Z")
On a similar note, at my graduate school, morning classes all started on the hour, and ended at ten minutes till, and afternoon classes all started at ten minutes after, and ended on the hour (I presume to ensure that even someone with a completely full schedule at least had 20 minutes for lunch in there somewhere)… Except that I taught an astronomy lab, which ran from 10 PM to midnight, and it was officially listed as 10:00 - 11:50. I’m guessing that that was also intended to avoid any issues with the date change. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 14, 2017, 12:44pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/49 "2017-05-14T12:44:51Z")
This all goes back to the difference between counting and measuring. Which is another way to say the difference (very roughly) between integers and real numbers. When counting stuff it often makes sense to start at 1. When measuring stuff, it (almost) always makes more sense to start at zero. The ancients didn’t really understand this distinction. And they often began by counting lumps of something they couldn’t yet measure continuously. And that’s how we \*inherit \*silly seemingly illogical systems. Such as 12am/pm and all the rest. They started out logical enough and then were incrementally extended past the limits of their own internal logicality. But eventually they/we did learn to measure whatever. And so today we know that a proper measuring-based approach to daily time uses 00:00:00.00000… as the origin and continuously counts up from there until the reset point is reached. Which is how almost the entire world except the USA does time today. So to directly answer the OP, the reason we \*use \*such an obsolete system today is that the USA is too friggin’ pig-stupid to join the 20th century, much less the 21st. ---
**Author:** ![D\_Anconia](https://avatars.discourse-cdn.com/v4/letter/d/67e7ee/32.png) [@D\_Anconia](https://boards.straightdope.com/u/D_Anconia)\ **Post date:** [May 14, 2017, 1:27pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/50 "2017-05-14T13:27:45Z")
> [@Enola\_Gay](#): > > Can you tell this to the airlines? This is where I always get into trouble–they have flights departing at 12:16AM or PM. If they used noon & midnight, this nonsense wouldn’t bother me so much. Which airlines routinely schedule flights at 12:16 am? ---
**Author:** ![Monty](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/monty/32/47_2.png) [@Monty](https://boards.straightdope.com/u/Monty)\ **Post date:** [May 14, 2017, 3:11pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/51 "2017-05-14T15:11:50Z")
> [@DPRK](#): > > BTW any reasonable calendar obviously has a year zero: for instance 0 a.d. = 1 b.c, -1 a.d. = 2 b.c., etc. Which calendars use “Year Zero”? ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [May 14, 2017, 4:15pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/52 "2017-05-14T16:15:19Z")
'Tis said that it is beyond human ability to sit down and design a system of time keeping _more_ convoluted and confusing than what we actually use … I believe I read that in the PHP manual at the beginning of the time function chapter … Tradition is terribly strong … sixty minutes in an hour … twenty-four hours in a day … how many days in a month depend of which month … crazy shit to be sure … but not so crazy if we remember much of this was laid down before zero was considered a number … and we used a base-60 system for counting … and a “third” was 1/60th of a second … It’s helpful to have some instant be designated at “zero time” … and present this time as “0” (or “0000” if you like) … if so, then the second after 23h 59m 59s will have to be 0h 0m 0s … as **LSLGuy** points out, we’re measuring time, not just counting it … using midnight is convenient, as traditionally this is when most everybody is asleep … except I suppose astronomers [giggle] … ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [May 14, 2017, 4:18pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/53 "2017-05-14T16:18:17Z")
> [@Channing\_Idaho\_Banks](#): > > The same reason the calendar starts at year one. There is no year zero just like there is no hour zero. Yes, there is. We just call it twelve. Maybe that originated before the concept of zero took hold? ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [May 14, 2017, 4:31pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/54 "2017-05-14T16:31:29Z")
I merely meant the trivial fact that, given a consistent year-numbering system (say, current year is 23, next year 24, etc), to date a historical event (23 years ago) arithmetic makes the year number 0 and then negative if you go far enough back. Sure, fancy concepts like zero and negative numbers may not be used in practice. AD years start at 1 to a historian; before that is BC. But the Maya had zeros in their Long Count. The Hindu and Burmese calendars have a year 0. (Some calendars do not use numbered years; they go by cycles.) Confusion about whether the “first” year is 0 or 1 certainly happens: witness the Buddhist year number in Burma versus Thailand. Re. confusion about the day, that reminds me, that’s nothing compared to not knowing what year it is! 1 January did not mark the beginning of the civil year in all places uniformly. In what year was George Washington born? ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [May 14, 2017, 4:31pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/55 "2017-05-14T16:31:51Z")
> [@Monty](#): > > Which calendars use “Year Zero”? [Astronomical\_year\_numbering]([Astronomy - Wikipedia](https://en.wikipedia.org/wiki/Astronomical) year numbering) (which in turn is the basis for forms of ISO 8601) [Holocene calendar](https://en.wikipedia.org/wiki/Holocene_calendar) These date years … -1, 0, 1 … Many traditional Asian calenders use a [year zero](https://en.wikipedia.org/wiki/Year_zero). Those either don’t deal with negative years at all or have an alternate method of referring to them. (E.g., using Gregorian years or dating from year zero of a previous era.) ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [May 14, 2017, 5:05pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/56 "2017-05-14T17:05:25Z")
> [@Monty](#): > > Which calendars use “Year Zero”? The [Khmer Rouge](https://en.wikipedia.org/wiki/Year_Zero_(political_notion))? Except that, when you check it out in detail, even they actually called it year 1! ---
**Author:** ![Enola\_Gay](https://avatars.discourse-cdn.com/v4/letter/e/3ab097/32.png) [@Enola\_Gay](https://boards.straightdope.com/u/Enola_Gay)\ **Post date:** [May 14, 2017, 5:39pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/57 "2017-05-14T17:39:26Z")
> [@D\_Anconia](#): > > Which airlines routinely schedule flights at 12:16 am? You’ve never heard of a redeye? ---
**Author:** ![Siam\_Sam](https://avatars.discourse-cdn.com/v4/letter/s/d78d45/32.png) [@Siam\_Sam](https://boards.straightdope.com/u/Siam_Sam)\ **Post date:** [May 14, 2017, 7:13pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/58 "2017-05-14T19:13:37Z")
> [@Enola\_Gay](#): > > Can you tell this to the airlines? This is where I always get into trouble–they have flights departing at 12:16AM or PM. If they used noon & midnight, this nonsense wouldn’t bother me so much. > [@D\_Anconia](#): > > Which airlines routinely schedule flights at 12:16 am? > [@Enola\_Gay](#): > > You’ve never heard of a redeye? Indeed. Flights at 12:01am are common at Bangkok’s Suvarnabhumi Airport, but never 12 midnight. I had a friend who ended up staying a day shorter because of this. He knew his flight was at night and on Thursday, so he thought it was on Thursday night. What he did not realize until just a couple of days before is that it was at a few minutes after midnight Thursday morning. Those are all long-haul flights that leave at that time. ---
**Author:** ![D\_Anconia](https://avatars.discourse-cdn.com/v4/letter/d/67e7ee/32.png) [@D\_Anconia](https://boards.straightdope.com/u/D_Anconia)\ **Post date:** [May 14, 2017, 8:51pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/59 "2017-05-14T20:51:03Z")
> [@Enola\_Gay](#): > > You’ve never heard of a redeye? Of course. But I’m genuinely curious where you’re flying from/to, and which airline. O’Hare is one of the busiest airports in the United States. Their concessions and other services generally shut down at 10 pm. Most of the doors to the departure areas are locked between 12 am and 5 am. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [May 14, 2017, 9:02pm UTC](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533/60 "2017-05-14T21:02:26Z")
> [@D\_Anconia](#): > > Of course. But I’m genuinely curious where you’re flying from/to, and which airline. > > O’Hare is one of the busiest airports in the United States. Their concessions and other services generally shut down at 10 pm. Most of the doors to the departure areas are locked between 12 am and 5 am. [Here’s a list of midnight to 5 am departures from ORD today.](http://chicago-ord.worldairportguides.com/flight-departures.php) ETA: Looks like you have to select it from the drop down menu. [Previous page](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533.md?page=2) [Next page](https://boards.straightdope.com/t/what-was-the-rationale-in-designating-midnight-as-12am/786533.md?page=4)