1-16-2008 Lecture 6 - -Yet he believed circular motion-De...

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Plato (428 – 348 BC) - All natural motion is circular - Reason is more important than observation - Mathematics Aristotle (384 – 322 BC) - Physics (sort of) - Elements o Earth o Water o Air o Fire o Quintessence Eratosthenes (276 – 195 BC) - He measured the circumference of the Earth. - His result of 42000 km is very close to the actual number: 40000km Claudius Ptolemy (AD 100 – 170) - Almagest (book) o Star catalogue o Instruments o Motions & model of planets, Sun, Moon - His model fit the data, made accurate predictions, but was very complicated. - Ptolemy’s Geocentric Model o Earth is at center o Sun orbits Earth o Planets move at different rates – some never get far from Sun (Venus, Mercury) o Complicated – can’t have just one celestial sphere – differing motions. o Planets orbit on small circles whose centers orbit the Earth on large circles – small circles are called epicycles – Explained retrograde motion 3.4 The Copernican Revolution Nicolaus Copernicus (1473 – 1543) - He thought Ptolemy’s model was contrived.
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Unformatted text preview: -Yet he believed circular motion-De Revolutionibus Orbium Coelestium-Copernicus’ Heliocentric Model o Sun is at center o Earth orbits like any other planet o Inferior planet orbits are smaller o Retrograde motion occurs when we “lap” Mars & the other superior planets o Simpler model than Ptolemy – but not better at predicting positions, since it assumed circular motion. Tycho Brahe (1546 – 1601)-Greatest observer of his day-Uraniborg (an astronomical/astrological observatory operated by Tycho Brahe)-Charted accurate positions of planets-Observed a supernova in 1572-Espoused a hybrid universe with Sun orbiting earth and the other planets orbiting the Sun. Johannes Kepler (1571 – 16300-Greatest theorist of his day-A mystic-There were no heavenly spheres-Forces made the planets move Kepler’s Laws 1. Each planet’s orbit around the Sun is an ellipse, with the Sun at one focus....
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