re: Why America Was Discovered
Eratosthenes made a very accurate estimate of the size of Earth, for his time, but...
"Eratosthenes wasn’t the only Greek who tried to measure the Earth. About a century later, Posidonius copied this feat, using the star Canopus as his light source and the cities of Rhodes and Alexandria as his baseline. Although his technique was sound, he had the wrong value for the distance between Rhodes and Alexandria, so his circumference came out too small. Ptolemy recorded this smaller figure in his geography treatise, where it was seized upon by Renaissance explorers looking for a quicker way to the Indies. Had Ptolemy used Eratosthenes’ larger figure instead, Columbus might never have sailed west."
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