How did ancient people know that the earth was round?
In: 37
So it all starts with the Greeks, though there is evidence it’s even further back from that. They looked up at the sky, particularly the moon, and said “That sure looks round to me… and so does the sun, while we’re at it… why WOULDN’T the Earth be?”
Along comes a smart guy we’ll call Eratosthenes because, well, that was his name. He learned that at midday, during the summer solstice in Syene, a stick stuck in the ground didn’t cast much of a shadow. So he asked himself “Eratosthenes, do you think this might be the case here in Alexandria where I am?” So he did the only sensible thing and stuck a stick in the ground at the same day and time. Lo and behold… there was a shadow. Well.. that’s not supposed to happen… So let’s look at that shadow… around 7 degrees or so. Interesting.
The Greeks had already figured out that however far away the sun was, it was a long freaking way, and shouldn’t have much effect on shadows of sticks. So if the shadow is 7 degrees, and I know how far it is from Syene to Alexandira, then I’ve got myself a sphere and I can work out how big it is with those numbers.
That’s exactly what he did, and he came up with a number that was less than 50 miles of what we now know to be the diameter of the Earth.
Latest Answers