If the Earth really was a sphere, Eratosthenes could use his observations to estimate the circumference of the entire planet. The idea of a spherical Earth was floated around by Pythagoras around 500 BC and validated by Aristotle a couple centuries later. And Eratosthenes probably already knew that. Now, if the sun's rays are coming in at the same angle at the same time of day, and a stick in Alexandria is casting a shadow while a stick in Syene is not, it must mean that the Earth's surface is curved. So, on June 21 he planted a stick directly in the ground and waited to see if a shadow would be cast at noon. He wondered if this were also true in Alexandria. A Greek mathematician and the head of the library at Alexandria.Įratosthenes had heard that in Syene, a city south of Alexandria, no vertical shadows were cast at noon on the summer solstice. In the mid-20th century, we began launching satellites into space that would help us determine the exact circumference of the Earth, 40,030 km.īut over 2,000 years earlier in ancient Greece, a man arrived at nearly that exact same figure by putting a stick in the ground. How an ancient Greek mathematician calculated the Earth's circumference. But over 2000 years earlier, a man in Ancient Greece came up with nearly the exact same figure using just a stick and his brain. In the mid-20th century, we began launching satellites into space that would help us determine the exact circumference of the Earth: 40,030 km. Account icon An icon in the shape of a person's head and shoulders.
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