Eratosthenes: The Man Who Figured Out the Size of the Earth

Ah, Eratosthenes, the man who figured out the size of the Earth without leaving his office. What a guy.

Eratosthenes was a Greek mathematician, geographer, and overall smarty-pants born in Cyrene (now modern-day Libya) in 276 BC. Like many ancient Greek scholars, he studied under Plato in Athens and eventually became the chief librarian at the Library of Alexandria. But it was his work in geography that really set him apart.

Legend has it that Eratosthenes was sitting in his office one day when he happened to notice that the sun was directly overhead at noon in the city of Syene (now Aswan, Egypt), but cast a shadow in Alexandria. This got him thinking, “Hmmm, I bet I could use this information to figure out the size of the Earth.”

And that’s exactly what he did. Using some clever geometry and the distance between Syene and Alexandria, he calculated that the Earth must be about 39,375 kilometers in circumference. Pretty impressive for a guy who didn’t even have GPS, am I right?

But Eratosthenes didn’t stop there. He also made important contributions to astronomy, cartography, and even music theory. Talk about a Renaissance man (or should I say Hellenistic man?).

Unfortunately, not all of his work has stood the test of time. He famously believed that the Nile River originated from underground springs, rather than from rainfall in the mountains. Oops.

Despite this blunder, Eratosthenes remains one of the most brilliant minds of the ancient world. And if you ever find yourself in need of calculating the size of the Earth without leaving your office, just remember: WWED (What Would Eratosthenes Do)?