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| universe is perfect, stars, planets, sun and moon perfect spheres, and constant velocity in circular motion |
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| Geocentric universe (earth is at the center), earth is a sphere because of curved shadow of earth seen during lunar eclipse |
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| earth's radius and diameter |
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| geocentry hypothesis, explained retrograde motion with series of deferents and epicycles |
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| plantes following a small circle that slides around a larger circle |
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| the larger circle that planets circle around in epicycles |
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| geocentric hypothesis, explained retrograde motion with series of deferents and epicycles |
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| the sun, not earth is the center of the universe |
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| rejected ptolemy, heliocentric model, correct order of planets from the sun, correctly defined interior and superior planets, dorrectly defined the cause of apparent retrograde motion (appears when the earth passes the planet at opposition) |
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| state of the art observatory, systematically measured positions of sun, moon and planets for 20 years |
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| used Brahe's measurements, abandoned perfectly circular motion, and constant orbital velocity, elliptical orbits, uniform "change" in velocity, 3 laws of planetary motion |
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| Kepler's Laws of Planetary Motion |
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Definition
1.) the orbits of the planets are ellipses with the sun at one focus
2.) a line connecting a planet to the sun sweeps out equal areas in space over equqal intervals of time (planets move faster at Perihelion, planets more more slowly at Aphelion
3.) the time that a planet takes to travel around the sun once is its orbital period, and its average distance from the sun equals the semimajor axis of its orbit, those two quantities are related |
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