Where did Ptolemy think earth was?

Answer 1

Don't get mad at him for being unsmart like everyone does. He placed the earth at the center of the celestial sphere contains 1025 fixed stars and 7 wanderers. His mathematical model is the most accurate model before Kepler. Everyone says that he used 80 or some huge number of epicycle to be accurate. No, he used 6 epicycles, 2 crank mechanisms, 6 eccenters, and 5? Equants. To compare with other, less accurate methods, Aristotle lovely homeocentric sphere had 34 or 45 components, and copernicus also used 34 rotating spheres. Some people, however thought that the eccenter and Equant violated Plato's idea of uniform circular motion, since this meant motion was not even, and not centered on the earth or a deferent. Al-Tusi, Al-Urdi and Ibn-Ash-Shatir made models based on the almagest which replaced the eccenter and Equant with epicycle, these models are also accurate, but do not comply with a physical model. One other thing is that no matter what you do with ptolemy's model, it is still geometrical, for the purpose of Astrology, and not a physical model. I spent an hour decoding the Equant, eccenter and epicycle into algebra, no matter what you do with the model, the calculating is hard.