No, not about the earth being round. Everybody who was anybody knew that in 1492. But, the reason Columbus got laughed out of the Portuguese court before visiting Ferdinand and Isabella of Spain was that he claimed the earth’s circumference was only about 17,000 miles, per Ptolomy.
Well, a few centuries before Ptolemy, and a couple millennia before Columbus, a Greek named Eratosthenes proved otherwise.
Yes, proved.
Depending on exactly how long you say the ancient Greek stadion was in modern units of measurement, he was either about 1.5 percent low or 3 percent high. But, he knew it was about 25,000 miles around the earth, not 17,000.
And, that’s not all this polymath did.
He was the first person to calculate the length of the year precisely enough that he knew a leap day was needed every four years.
And, he took the first serious stab at the Earth-Sun distance.
For more about his discoveries, read the story or read his read the story.
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