I wonder when was the concept equivalent to our modern 'time zones' discovered, or at least that the time at one place is not the same as everywhere else.

Meaning that people became aware of differences for 'local true high noon', or in other words that the local time for the zenith of the sun would systematically differ from place to place on a line from East to West — depending on what we now call the meridian.

I'm guessing that that discovery came at about the time where instant communication was created (Telegraph/radio) or when at least people could move fast enough around the globe to not take days to cross what would be an hour time difference today.

So is there any recorded moment in history where that time difference was discovered? Am I right to think that this was unknown before information could travel fast enough that it would be known that when you type something from Paris to Moscow, even if for you its the evening the person you are writing to might be already gone to bed?

EDIT: To rectify: I'm not asking for when was latitude figured out. I'm asking when was the realisation made that the time where you are is not the same as everywhere else on earth.

  • 31
    Time zones aren't some kind of mysterious law of nature. They are something we humans dreamt up to deal with the fact that we insist on keeping our time relative to overhead sun position even though we are capable of traveling far enough across the earth in a day to make that a very poor method of timekeeping. (Not to mention traveling away from the earth entirely, or any of the myriad of other reasons).
    – T.E.D.
    Commented Jul 13, 2021 at 17:23
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    @MCW I think the answers are a bit mislead by this slightly too modern modern/anachronistic word choice/reading of 'timezone'. My best guess for now, based on my understanding of the Q, is that QP looks for an ancient ~'Greek/Sumerian' source noticing that ~'true local high noon/'Sun's Zenith' comes later if you get further West'? Commented Jul 13, 2021 at 18:00
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    I think you need to distinguish between discovered and the need to have a common time in a wider area. The railways brought the latter into focus. In Prussia this started on the 18th of January 1848 with the introduction of the Berlin time for the railways (6 minutes 24 seconds differnce to CET) and lasted until 1893 when CET replaced all local times. Commented Jul 13, 2021 at 21:23
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    Note that the (late 18th century) chronometric answer to the longitude problem pretty much by definition implies this knowledge. So it has to be at least that old. I always assumed that it was the ancient Greeks (or even Mesopotamians) who figured it out, but wasn't sure how they could manage it at the time; in retrospect using lunar eclipses makes sense. (Columbus famously did exactly this in 1504.) Commented Jul 14, 2021 at 9:21
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    The amount of people here that apparently only read the subject and not the body is astounding. Is the subject worded poorly? Sure. Does the body of the post make it clear? Definitely. Commented Jul 14, 2021 at 14:36

6 Answers 6


The concept of longitude was first developed by ancient Greek astronomers. Hipparchus (2nd century BCE) used a coordinate system that assumed a spherical earth, and divided it into 360° as we still do today. His prime meridian passed through Alexandria. He also proposed a method of determining longitude by comparing the local time of a lunar eclipse at two different places, thus demonstrating an understanding of the relationship between longitude and time.

Longitude: History.

Eratosthenes in the 3rd century BCE first proposed a system of latitude and longitude for a map of the world. His prime meridian (line of longitude) passed through Alexandria and Rhodes, while his parallels (lines of latitude) were not regularly spaced, but passed through known locations, often at the expense of being straight lines.

By the 2nd century BCE Hipparchus was using a systematic coordinate system, based on dividing the circle into 360°, to uniquely specify places on Earth. So longitudes could be expressed as degrees east or west of the primary meridian, as we do today (though the primary meridian is different). He also proposed a method of determining longitude by comparing the local time of a lunar eclipse at two different places, to obtain the difference in longitude between them. This method was not very accurate, given the limitations of the available clocks, and it was seldom done – possibly only once, using the Arbela eclipse of 330 BCE. But the method is sound, and this is the first recognition that longitude can be determined by accurate knowledge of time.

History of longitude: Longitude before the telescope.

Eratosthenes created the first global projection of the world, incorporating parallels and meridians based on the available geographic knowledge of his era.


His third book of the Geography contained political geography. He cited countries and used parallel lines to divide the map into sections, to give accurate descriptions of the realms. This was a breakthrough and can be considered the beginning of geography. For this, Eratosthenes was named the "Father of Modern Geography."

Eratosthenes: Geography.

One of the earliest known descriptions of standard time in India appeared in the 4th century CE astronomical treatise Surya Siddhanta. Postulating a spherical earth, the book described the thousands years old customs of the prime meridian, or zero longitude, as passing through Avanti, the ancient name for the historic city of Ujjain, and Rohitaka, the ancient name for Rohtak (28°54′N 76°38′E), a city near the Kurukshetra.

The notion of longitude for Greeks was developed by the Greek Eratosthenes (c. 276 BC – c. 195 BC) in Alexandria, and Hipparchus (c. 190 BC – c. 120 BC) in Rhodes, and applied to a large number of cities by the geographer Strabo (64/63 BC – c. 24 AD). But it was Ptolemy (c. AD 90 – c. AD 168) who first used a consistent meridian for a world map in his Geographia.

Ptolemy used as his basis the "Fortunate Isles", a group of islands in the Atlantic, which are usually associated with the Canary Islands (13° to 18°W), although his maps correspond more closely to the Cape Verde islands (22° to 25° W). The main point is to be comfortably west of the western tip of Africa (17.5° W) as negative numbers were not yet in use. His prime meridian corresponds to 18° 40' west of Winchester (about 20°W) today. At that time the chief method of determining longitude was by using the reported times of lunar eclipses in different countries.

Prime meridian: History.

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    So basically the ancient greeks, when they figured out the earth was round they also figured out that if the earth is round and spinning on its axis, then well people on the other side of the world must be living at a different time than them.
    – Fredy31
    Commented Jul 13, 2021 at 20:14
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    @Fredy31, more or less. We know that Hipparchus made the connection between longitude and time; we don't know if anyone earlier did, while we do know that the concept of a spherical Earth is about 300 years older than him.
    – Mark
    Commented Jul 14, 2021 at 2:47
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    @Fredy31 They didn't know Earth was spinning, they thought the rest of the universe was revolving around it, but the difference is not significant. All that matters is that the Sun couldn't be directly over all places at the same time.
    – Barmar
    Commented Jul 14, 2021 at 14:36
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    You should include a lede (summary), in your own words, at the top of this answer.
    – Spencer
    Commented Jul 14, 2021 at 19:11
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    @DanM. Even if they didn't need it, they might have known about it. The Babylonians were very interested in recording and predicting eclipses (recorded as early as 1375 BCE) and certainly if people were recording eclipses always taking place earlier in the west and later in the east, that would be interesting. Especially with travelers going further away, so it would be more obvious that it was definitely earlier and later. Commented Jul 15, 2021 at 16:09

Time zones were not discovered, they were defined. Without time zones, you have the concept of solar noon. A time zone is an area where the solar noon of a central place (like a royal observatory) is applied in a wider area.

This became relevant with railway timetables. A train leaves at 12:00, travels for 60 minutes, and the clock at the destination should show 13:00. The opposite of this is used for navigation at sea. The time of noon is compared to a clock on the ship and the difference is used to calculate the longitude.

Different time zones happen when it is no longer feasible to apply central time to outlying areas, and a line gets drawn -- often in one hour increments, so that at least the minutes match. At times, in half-hour or different increments. Compare the Russian and Chinese decisions in this regard.

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    Please expand on the science history of true/local 'solar noon', as I guess that's what's really asked about? Where was that first noticed, how, and who wrote that observation down, explained it etc? Commented Jul 13, 2021 at 18:03
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    @LаngLаngС, you edited the OP's question and now ask me to answer your edit. I think I had answered the original.
    – o.m.
    Commented Jul 13, 2021 at 19:01
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    Maybe. I hope the edit better captures QPs intentions. We'll see that. Even for the first version I think your emphasis on solar noon is exactly right— but could use expansion anyways. Feel free to ignore this heads up, it's your A after all. Commented Jul 13, 2021 at 19:18
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    The Wikipedia article on railway time addresses the 2nd para, which probably describes when it became relevant to ordinary people. The UK's Network Rail has a little more. Living in one of the cities that first experienced railway time, it's local history for me, and I have used the time difference in solar navigation
    – Chris H
    Commented Jul 14, 2021 at 8:29
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    I think this answer doesn't grasp the original question. In focusing on the facts of "time zone," it omits the fact that the OP says, "time zones, or at least that the time at one place is not the same as everywhere else." I interpret this to mean something more basic than our modern concepts of time zones. When did people anywhere on the planet first realize that there are people living so far away that their time of day differed much from their own? Now, maybe that realization didn't ever occur until the concept of Longitude wa understood. But if it did occur, when did it occur?
    – ttonon
    Commented Jul 14, 2021 at 19:36

I point out that the survivors of the Magellan expedition were startled by a date discrepancy.

Twenty crewmen died of starvation by 9 July 1522, when Elcano put into Portuguese Cape Verde for provisions. The crew was surprised to learn that the date was actually 10 July 1522,[104] as they had recorded every day of the three-year journey without omission.


The full extent of the globe was realised, since their voyage was 14,460 Spanish leagues (60,440 km or 37,560 mi). The global expedition showed the need for an International Date Line to be established. Upon arrival at Cape Verde, the crew was surprised to learn that the ship's date of 9 July 1522 was one day behind the local date of 10 July 1522, even though they had recorded every day of the three-year journey without omission. They lost one day because they travelled west during their circumnavigation of the globe, in the same direction as the apparent motion of the sun across the sky.[150] Although the Kurdish geographer Abu'l-Fida (1273–1331) had predicted that circumnavigators would accumulate a one-day offset,[151] Cardinal Gasparo Contarini was the first European to give a correct explanation of the discrepancy.[152]


Andhere is a link to a similar question and its answers:


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    And of course fictional Phileas Fogg had the opposite surprise in 1872 (though of course one wonders how you could miss the date change while crossing the US mainland at the very least)
    – jcaron
    Commented Jul 15, 2021 at 14:18
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    I was once there when someone (otherwise an ordinary person) was started to realize that "Cinnabon" was called that because ... cinnamon... buns... So "someone didn't realize this before now" can be more of a reflection on the individual than the state of known technology at the time. Commented Jul 15, 2021 at 14:20
  • I was once there when someone figured out that "Tums" are so-called because they make your tummy feel better. (It was me, and I am otherwise an intelligent person, I like to think.) Commented Mar 4, 2022 at 16:49

There is no recorded moment, but the time difference in places with different longitude was discovered as soon as people realized that the Earth is round, and that Sun rotates about it (or vice versa, which does not matter for this question). We do not know when exactly did this happen, since almost all astronomic and geographic literature from the ancient Greece is lost. But we know that this was a common knowledge in the Hellenistic Greece. Hellenistic historians of science probably already did not remember who exactly discovered this and when, so they tended to attribute this to Pythagoras, one of the two earliest scientists they knew (the other was Thales).

Modern time zones were formally decided in the Anglo-French Conference on Time keeping at sea in 1917.

Before that people just used local time at some given location, or in large countries like the US and Russia, established their own time zones. The necessity of doing this came with the spread of railroads.

  • so the time difference has been known for so long that the person that discovered it, or first theorised it is lost to history? Like the fact that water is wet?
    – Fredy31
    Commented Jul 13, 2021 at 16:19
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    I was unaware that latitude was relevant. I thought time zones were defined from longitude when trains made them relevant.
    – MCW
    Commented Jul 13, 2021 at 16:29
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    This is wrong. Latitude is the angle north or south of the equator, and has nothing to do with time. It was important in Eratosthenes' calculation of the Earth's circumference, which he did by measuring the sun's angle at two places on a north/south line. So he must have deduced the time difference (as defined by solar noon) from the fact that the Earth is a sphere, even if he couldn't have experienced it directly. en.wikipedia.org/wiki/…
    – jamesqf
    Commented Jul 13, 2021 at 16:43
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    This was a misprint: I wrote lattitude instead of longitude:-) I corrected.
    – Alex
    Commented Jul 13, 2021 at 18:59
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    By 1900, most standard time zones in Europe and North America had already been established by the railroads. For most countries the formal adoption (per law) came later. So 1917 is misleading (at least on land). Commented Jul 13, 2021 at 20:50

Before high precision clocks and coordinated clock synchronization procedures, local times differed not just because of a different latitude, but also randomly, due to inaccuracy of clocks. But the same inaccuracy of clocks was mostly hiding the differences.

Without a coordinated synchronization mechanism, each authoritative clock (without an even more authoritative "parent" clock) forms its own time zone. It is roughly dependent on an astronomical source, but in a way that's not necessarily terribly precise, or scientifically defined, or consistently maintained.

The clock may or may not travel and so does its time zone (sphere of authority).


At least over 4000 years ago probably much longer. The 3000-4000 year 'discovery' times given above was due to archeological and written proof, but as at that point it was already a well known and developed idea (just as spherical earth). An educated guess, would for the earliest date, would probably be at least 100,000 years ago. As the first person to travel far enough and looked up would easily realize that the suns position at noon was no longer the same. As 100,000 years ago humans first left Africa, by that point enough humans would have traveled far enough to make times of day change by travelling (i.e. time zones) to be recognized. But deciding to need the use of time zones on land started with the speed of the railroads. As for at sea, the sun changing position was used for navigation at the latest during the late bronze age, so at least 3500 years ago (and sun changing position at same time of day = time zones).

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    -1 Skeptical. 100K years ago how would someone keep time accurately enough to determine "the suns position at [another location's] noon"? If you have a citation and edit your answer, maybe that could be improved. Commented Jul 14, 2021 at 14:45
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    The problem here is, in the absence of clocks or some globally-constant-time events (eg lunar eclipses), "sun changing position at same time of day" isn't possible because "time of day" is defined with reference to the sun!
    – AakashM
    Commented Jul 14, 2021 at 15:28
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    Before the invention of timekeeping devices, noon was whenever the sun was highest in the sky - there was no such thing as "clock noon". By definition, you could not observe the sun in any other position at noon, since if the sun is elsewhere, it is not noon. You'd need a method to accurately time the duration between noons and then notice that the duration changed when moving east or west a significant distance, but no one had such devices 100k years ago. Commented Jul 14, 2021 at 15:44
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    So how would this 100K year old human know when it was supposed to be noon, look at his watch? Commented Jul 14, 2021 at 21:48
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    Personally I've travelled through multiple time zones in one go via slow methods (i.e. not a plane) which I guess is the idea behind this theory and I have no idea how I would notice the time difference without a watch.
    – Voo
    Commented Jul 15, 2021 at 15:57

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