Before you ask, no I didn’t have any encounters with people who claimed Earth was flat. I’m just curious.
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It was conclusively proven when Ferdinand Magellan’s expedition (minus Ferdinand) circumnavigated the globe in 1522.
However, it had been widely believed in the west for nearly 2000 years before that. Greek cartographers had already noted that the sun is at a steeper angle in Egypt than it is in Macedonia, and used that angle to calculate the size of the sphere with good accuracy.
Early astronomers also suspected that lunar eclipses were caused by Earth’s shadow, which is visibly round.
Contrary to popular belief, Columbus wasn’t warned he’d fall off the world – his sponsors were (correctly) worried that he had miscalculated the distance from Spain to China and would never make it. He wouldn’t have, but was saved by a previously unknown landmass that allowed a resupply.
There was once a man named Eratosthenes in Ancient Greece.
He found in some books a record of a notable occurrence in a town called Syene, in which on the summer solstice at noon, objects would not cast shadows, and you could look all the way down wells.
He realized that meant the sun would have to be EXACTLY overhead in that moment, and since he knew for a fact that on that day and time in Alexandria (where he was) shadows DID get cast, he realized that the apparent angle of the sun must be changed with the distance. The only way this would work would be if the Earth were a sphere.
Since Syene was almost directly south of Alexandria, he took the known distance between to two towns, and the length of shadows in Alexandria on the solstice, and using some Trigonometry found the size of the Earth.
He was less than 1% off modern figures with this crude method
Well, it was theorized by Eratosthenes of Cyrene around 270 b.c.
He even calculated the circumference of the earth with a really smart technique involving the sun, shadows, a stick and a camel; he got it wrong by a really small margin, which is pretty impressive
More on the experiment:
Also, any ancient people could have looked up at the moon during an eclipse and seen that the shadow was curved, so the earth must be round.
It was known at different times in different places. In the ancient near east, the world was thought to be flat. The ancient Greeks clearly knew it was round, going back even before Eratosthenes who did a good job estimating its size. The first mention comes from about 500 BC. India seems to have adopted the “spherical earth” model (thought they might have got it from Greece), but China did not until European contact became extensive.
So why did Greece get it so early and some other countries get it quite late? I’d suggest it was because Greek philosophers were quite obsessed with geometry and also relatively likely to sail around a lot. The spherical nature of the earth is easier to pick up if you are sailing around a lot and seeing different stars at different latitudes or the tips of islands appear first, and it’s easier to know what that means if you have an understanding of geometry.
The way some people learned was seeing a lunar eclipse. In a lunar eclipse, the Earth’s shadows reflects off the moon and when people saw it they figured out the Earth was round. Not sure the exact date but definitely the BC years.
While it was common knowledge by 1500, an official proof was a Spanish explorer named Magellan circumnavigated, or sailed around the Earth.
Another commonly recognized method for discovering the Earth’s roundness was a discovery in Ancient Greece around 500 BC. A scholar named Eratosthenes, he heard of a city (Syene) where on the summer solstice, when the sun was directly above the Earth, and he wanted to see if where he was the same would happen. However when he placed a stick in the center of the city, he found a 7.2 degree angle of shadow. If the Earth was flat, and the sun was directly overhead, because the sun is bigger than Earth, then the whole world would have no shadow. So he discovered that the Earth had to be round in order for the sun to have a shadow during the summer solstice.
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