# Who decided what time it is? **URL:** \ **Category:** Factual Questions\ **Created:** [August 4, 2002, 11:09pm UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343 "2002-08-04T23:09:04Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![rostfrei](https://avatars.discourse-cdn.com/v4/letter/r/7bcc69/32.png) [@rostfrei](https://boards.straightdope.com/u/rostfrei)\ **Post date:** [August 4, 2002, 11:09pm UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/1 "2002-08-04T23:09:04Z")
As I glance at my watch, I see that it’s 7:02 pm EST. Says who? I went to [www.time.gov](http://www.time.gov) and they have the time, to the exact second. How did “they” determine that it was exactly 19:03:25? When the first watch/wristwatch was invented, how did they know what time to set? Eric ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [August 4, 2002, 11:51pm UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/2 "2002-08-04T23:51:30Z")
The time of day of any given spot on the Earth is determinded by it’s position relative to the sun. Noon is when its closest, midnight when its farthest. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [August 4, 2002, 11:57pm UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/3 "2002-08-04T23:57:54Z")
GMT (Greewich Mean Time) is (for practical purposes of this thread) the time when the mean sun crosses the Greenwich meridian. [http://greenwichmeantime.com/index.htm](http://greenwichmeantime.com/index.htm) ---
**Author:** ![Lodrain](https://avatars.discourse-cdn.com/v4/letter/l/c4cdca/32.png) [@Lodrain](https://boards.straightdope.com/u/Lodrain)\ **Post date:** [August 5, 2002, 2:27am UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/4 "2002-08-05T02:27:08Z")
No, **Hail Ants** , not really; noon is when the sun is at its zenith - a point where the sun will cast no shadow, and midnight at its nadir - directly opposite from noon, on the other side of the Earth. The Sun is closest around mid-winter and farthest mid-summer. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [August 5, 2002, 2:33am UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/5 "2002-08-05T02:33:52Z")
The sun casts shadows at noon, just not in an easterly or westerly direction. It is easy, then, to tell when noon is at a given point on the earth, assuming you know where west and east are. Originally, every place just went by their own “local noon.” This got difficult when railroads needed to coordinate with each other to prevent them crashing into one another, so time zones were invented. Timezones roughly follow lines of longitude such that noon in the time zone matches the local noon midway between the two boundaries of the zone. ---
**Author:** ![Neptune](https://avatars.discourse-cdn.com/v4/letter/n/b5a626/32.png) [@Neptune](https://boards.straightdope.com/u/Neptune)\ **Post date:** [August 5, 2002, 3:33am UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/6 "2002-08-05T03:33:36Z")
It gets more complicated than that. Google “leap seconds” and “maser”. ---
**Author:** ![Aspidistra](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aspidistra/32/3894_2.png) [@Aspidistra](https://boards.straightdope.com/u/Aspidistra)\ **Post date:** [August 5, 2002, 6:20am UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/7 "2002-08-05T06:20:29Z")
> [@](#): > > \*Originally posted by Lodrain \* > \*\*No, **Hail Ants** , not really; noon is when the sun is at its zenith - a point where the sun will cast no shadow, and midnight at its nadir - directly opposite from noon, on the other side of the Earth. The Sun is closest around mid-winter and farthest mid-summer. \*\* No, **Lodrain** , not really \*; midsummer is when the tilt of the earth is such that you get the maximum hours of sunlight in one day. It doesn’t have anything to do with the proximity of Earth to the sun otherwise the seasons would be the same in both hemispheres. Coincidentally, I was having a discussion with some friends on this very point (how much of a contribution the Earth’s elliptical orbit makes to the seasons) just last night. We concluded that a) The earths orbit is so close to circular that there’s probably no measurable effect b) In any case, it would be a wild coincidence if the closest point was aligned with the Earth’s tilt so that it occurred in either hemisphere’s summer, and c) If there’s any precession in the orbit, it wouldn’t even happen at the same time every year. Not that this has anything to do with the OP… \*sorry, couldn’t help myself there ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [August 5, 2002, 6:43am UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/8 "2002-08-05T06:43:35Z")
> [@](#): > > \*Quoth Aspidistra \* > **midsummer is when the tilt of the earth is such that you get the maximum hours of sunlight in one day. It doesn’t have anything to do with the proximity of Earth to the sun otherwise the seasons would be the same in both hemispheres.** True though this is, **Lodrain** ’s statement is also true, for the Northern hemisphere. Note that **Lodrain** did not claim that the proximity to the Sun _caused_ the seasons. In response to your conclusions: a) That’s pretty much correct. b) The closest point (so-called _perihelion_) does in fact occur in the Southern hemisphere’s Summer. It’s not a wild coincidence. c) There is precession, but it occurs at a period of 21,000 years (I think). It will be a few thousand years before (b) is no longer true. ---
**Author:** ![Lodrain](https://avatars.discourse-cdn.com/v4/letter/l/c4cdca/32.png) [@Lodrain](https://boards.straightdope.com/u/Lodrain)\ **Post date:** [August 5, 2002, 7:23am UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/9 "2002-08-05T07:23:07Z")
Oops. The main problem I had back there was a naming problem - I knew that in my neck of the woods, the perhelion occured in summer, in the middle somewhere, but forgot the exact date, so, I decided to be Shakespearean and say ‘midsummer’. Sorry. ---
**Author:** ![Futile\_Gesture](https://avatars.discourse-cdn.com/v4/letter/f/f05b48/32.png) [@Futile\_Gesture](https://boards.straightdope.com/u/Futile_Gesture)\ **Post date:** [August 5, 2002, 9:26am UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/10 "2002-08-05T09:26:30Z")
All the definitions given so far ar interesting, but what really defines your and my, and everyone else on the planet’s time is the [BIPM](http://www.bipm.fr/enus/5_Scientific/c_time/time_server.html) . They are the international organisation based in France, that is responsible for Coordinated Universal Time, which is the basis used by every time zone. ---
**Author:** ![Triskadecamus](https://avatars.discourse-cdn.com/v4/letter/t/b19c9b/32.png) [@Triskadecamus](https://boards.straightdope.com/u/Triskadecamus)\ **Post date:** [August 5, 2002, 9:35am UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/11 "2002-08-05T09:35:39Z")
In the United States, it’s the US Naval Observatory, by act of Congress, the authority on the question, “What time is it?” [Time.gov](http://Time.gov) is becoming the default source for that information, and is very closely associated with the Naval Observatory. Tris ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [August 5, 2002, 9:46am UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/12 "2002-08-05T09:46:19Z")
From the link cited by futile gesture: " > [@](#): > > International Atomic Time (TAI) is calculated by the BIPM from the readings of more than 200 atomic clocks located in metrology institutes and observatories in more than 30 countries around the world. > > Coordinated Universal Time (UTC) is the basis for legal time worldwide and follows TAI (see below) exactly except for an integral number of seconds, presently 32. These leap seconds are inserted on the advice of the International Earth Rotation Service (IERS) ([http://hpiers.obspm.fr](http://hpiers.obspm.fr)) to ensure that, on average over the years, the Sun is overhead within 0.9 seconds of 12:00:00 UTC on the meridian of Greenwich. UTC is thus the modern successor of Greenwich Mean Time, GMT, which was used when the unit of time was the mean solar day. I am glad to know there is an “Earth Rotation Service” to keep the world going around. I assume they use money to do this. ---
**Author:** ![RedNaxela](https://avatars.discourse-cdn.com/v4/letter/r/ad7895/32.png) [@RedNaxela](https://boards.straightdope.com/u/RedNaxela)\ **Post date:** [August 5, 2002, 2:12pm UTC](https://boards.straightdope.com/t/who-decided-what-time-it-is/122343/13 "2002-08-05T14:12:51Z")
**Sailor** : Nah, they probably use love.