How did ancient people know that the earth was round?
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And then we get modern people with the power of the world intellect at their finger tips decide to use it to look at a dubious YouTube video created by a random Smurf in his basement to decide that the world is flat, and presumably on the back of giant turtles or something
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Science, specifically Observing, theorizing and testing.
Most others covered observation, so I’m skipping ahead. Ancient people observed other celestial bodies and realized they may be similar to the Earth under their feet.
So now we assume earth is round, how do we verify this? You test it! This is the easier step, we simply coordinate two people on the same day run the same experiment at different locations.
The specific test was measuring shadows at the same time. The fixed items were time of day, altitude, sticks and longitude. Latitude was the variable. So two people made measurements at two cities and used shadows to triangulate the sun and their two locations. The math showed the person further north was further from the sun, therefore you can conclude the Earth is not flat.
Additionally, if the Earth was flat, we wouldn’t have a day-night cycle. Look at flat earthers model of a disc and a sun spinning circles above. On the same plane, they say half the surface is day and half is night. How does sunlight just stop and not shine on half the planet? Hold a plate under a light bulb and try to make half lit and half shaded on the same face. Impossible.
While not a direct answer to your question, you might find it interesting to know that the Chinese name for Earth literally translates as “dirt ball” (地球）。
watch this Carl Sagan video, it answers tis question https://youtube.com/shorts/T0f6u39jlRA?feature=share
It’s time you discovered Carl Sagan’s Cosmos. It’s a brilliant piece of art, and you’ll learn the answer to this and many more questions. Enjoy!
Ancient people had the same brain power we have now. I’d actually said the average ancient was alot smarter then the average person now, being dumb then meant death, or at least great suffering.
My understanding is that they used observations of shadow length of obelisk at different locations at specific times of the day on the summer solstice. Obilisks closer to the equater would have smaller shadows than those further away. This can’t happen on a flat surface, but does happen on the surface of a sphere. Using these observations they were able to extrapolate not only the shape of the planet, but the size as well…. to within a working accuracy.
Eratosthenes of Cyrene calculated the radius of the planet pretty accurately by noting that on a given day the sun shown directly down a well in Aswan at noon, and then measured the angle of the sun’s shadow at noon on the same day in Alexandria – about 500 miles away. A bit of math gave a circumference of 25,000 miles. That was ~250 BCE.
Posidonius of Rhodes calculated it by observing the star Canopus, which when it’s on the horizon in Rhodes it was a certain distance above the horizon in Alexandria. His calculations showed a circumference of 18,000 miles.
Columbus knew about Posidonius’ estimate, but not Eratosthenes’ which is why he thought he had travelled farther than he actually had.
Define “ancient.” I don’t think Neanderthal would really travel far enough to care and by the time we were building boats if you could go far enough to not see land anymore but turn around and come back to it you could probably figure out why.
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