I heard time zones were invented in order to deal with the issue of transcontinental railway schedules. But before the need of such time table, I assume people realized solar noon was earlier in some places and later in other places. If anything, it follows from the idea that the earth is round and that the sun revolves around the earth. Were there practical implications for that knowledge? (Say, religious rituals needing to be performed at the same time throughout a large empire?) Who are the people who discovered this fact? How did they do so? (Astronomical models? "precise" clocks? Something else?)
Thanks.
I've actually answered this question before. With the idea that the earth is spherical(ish)^1, which was known in antiquity, comes the idea that the sun illuminates the globe at different times. To shamelessly steal from this older answer.
Hipparchus of Nicaea (c. ~190-120 BCE) seems to have been the first person to propose using a grid system to find the position of cities (and other places) on a globe, which implies an understanding of longitude. He built on earlier work by Eratosthenes of Cyrene (c. 276-194 BCE), who had mapped the known Earth, including finding its circumference. Hipparchus' method of finding the longitude of places was to use the differences in timing of lunar eclipses at different points on the globe to calculate the difference between local time of those points; the drawback is that there was no accurate-enough method of timekeeping to lead to useful calculations. Edit to clarify: The difference in local time between observed beginning and end of the eclipses would serve, essentially, as a way to understand the longitude between places.
The knowledge that local time would be different at different points on the globe is what led eventually to what's called "the discovery of the longitude" in around 1760 or so, when two methods of reliably finding longitude using time were discovered and implemented.
1: The earth isn't a perfect sphere, some Reddit pedants have taken me to task over this before.