Chapters 3 and 4

Chapters 3 and 4 - Motions of Planets and Gravity (Chapters...

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“Geocentric View” Aristotle and ~2,000 yrs after him! Orbits of planets were thought to be circular If this were true, how would the brightness of planets appear--would it stay constant or would it vary with time? Motions of Planets and Gravity (Chapters 3, 4)
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planets vary in brightness and apparent size! So they can’t be at fixed distances (as in circular orbits) from Earth! But in real life,
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In fact, some planets even show retrograde motion!
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How could one allow a planet to go backward and have variable brightness with circular orbits?
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The Greeks devised epicycles and deferents to vary distances of planets from Earth and to explain retrograde motion!
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Ptolemy’s model (AD 140) Most successful geocentric model, but needed a huge number of circles/spheres Too complicated to be “elegant”! Still survived for 13 centuries!
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So what killed the Geocentric Theory? Galileo’s observations, popularized by him Kepler’s laws: Fits to planetary orbits Measurements of stellar parallax (and of course modern space probes)
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How would we explain retrograde motion in the heliocentric theory?
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Understanding Retrograde Motion in terms of Heliocentric Model
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Venus Phases Venus shows phases from full Venus to new Venus. Could this be explained if Venus and the Sun revolved around the Earth?
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Who revived the helio-centric model? Did it agree with the data?
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Chapters 3 and 4 - Motions of Planets and Gravity (Chapters...

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