Episode 20: The Theory of Epicycles & Deferents

In the Hellenistic Era the astronomer Apollonius of Perga (maybe) developed the model of epicycles and deferents that was to dominate Western astronomy for more than 1500 years. Around the same time, Eratosthenes, who was the head librarian at the Library of Alexandria, developed a novel technique to measure the circumference of the Earth and arrived at a suspiciously accurate result.