When were 'time zones' (or at least time difference) discovered?

Question

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.

Answer 1

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.

— Eratosthenes.

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.

Answer 2

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.

Answer 3

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.

https://en.wikipedia.org/wiki/Magellan_expedition#Return_to_Spain[1]

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]

https://en.wikipedia.org/wiki/Magellan_expedition#Scientific_accomplishments[2]

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

https://hsm.stackexchange.com/questions/13539/at-what-time-people-relized-the-changes-in-times-between-countries/13543#13543[3]

Answer 4

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.

Answer 5

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).

Answer 6

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).