I get how time zones were established, and I get how people knew the earth was round thousands of years ago, so I assume that it was hypothesized that some areas of earth were darker/lighter than others at the same time. I feel like it was kind of unprovable though due to limitation. At what point did we actually confirm that it was indeed night time somewhere else when it was daytime on the opposite side of the world? And how was the found out?
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Probably when they stood on mountaintops and watched the sunrise draw its way across the land. Probably the question you don’t even realize you’re asking is when people started to understand the concept of “time” in the way you’re thinking of it – but it would have been a long, long time ago that people first knew something like “sunrise way up here on top of this hill is before sunrise for those people down in that deep valley”
I forgot how to look it up, but it was when ancient scientists compared records on eclipses from different regions of the world and found that their timing differed – for example, one record said the eclipse began when the Moon was high in the sky, and another that the same eclipse started just after moonrise.
Unfortunately, we don’t know. Much like ancient people figuring out the shape of the earth, with these ideas just suddenly showing up in writing as already established, if not fully understood, ideas.
Its likely these sorts of ideas originated earlier than written language, meaning we will never know the ultimate source of the idea.
There were a lot of early observations.
Like u/Xemylixa says, the “proof” is that a solar eclipse would occur nearly simultaneously in Anatolia and India, but one would report it at sunset and the other says it happened at noon.
But you dont need rare events to make an educated guess. The ancients had calculated that the earth was round by measuring shadows at noon in Egypt and Greece on the same day and getting different angles. They also knew that the days were much longer in the winter in Egypt than they were in the barbarian lands to the far north.
From this they correctly guessed that the Earth was a sphere illuminated from a distant light source and even attempted to calculate the “height” of the sun by triangulation of the sun’s rays at different locations, but it’s so unfathomably far that they could never measure angles accurately enough to estimate the distance beyond “really, really high”
>*”darker/lighter on other parts … at the same time?”.*
The phases of the moon give the game away. There are lunar calendars from the stone-age.
Carl Sagan did a visual example of how Eratosthenes created an experiment that figured out a few things about how big the Earth was, and it’s position revolving around the sun.
Even before it was widely accepted that the Earth is round, people knew that the Sun was the source of light. They could also observe the lunar day on the Moon and see how it was never truly fully illuminated. So if you know there is a single light source, you know the Earth is round and you also have a visual example of how a round body is illuminated by a single light source, the rest kinda just falls into place.
This question has been asked here before.
The answer is “basically among learned people if they ever thought about it, they knew”
People knew the earth was round and that the sun shone down.
There was VERY little need for this information, it is almost impossible to leverage in any way in the ancient world.
But the ancient Greeks were trying to measure it. You can be sure pre historical societies simply implicitly knew this fact if they cared to think about it.
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