Astronomy Lecture 9:17

Astronomy Lecture 9:17 - motions Kepler first tried to...

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9/17/10 Chap 3 Notes from Lecture Underpinnings of the Greek geocentric model: Earth at the center of the universe Heavens must be “perfect”: Objects moving on perfect spheres or in perfect circles. This made it difficult to explain the apparent retrograde motion of planets. Over a period of 10 weeks, Mars appears to stop, back up, and then go forward again. How did Copernicus, Tycho, and Kepler challenge the Earth-centered model? Proposed a Sun-centered model Used model to determine layout of solar system The model was no more accurate than the Ptolemaic model in predicting planetary positions, because it still used perfect circles. Compiled the most accurate naked eye measurements ever made of planetary positions Still could not detect stellar parallax, and thus still thought Earth must be a center of the solar system. Hired Kepler, who used Tycho’s observations to discover the truth about planetary
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Unformatted text preview: motions Kepler first tried to match Tychos observations with circular orbits But an 8-arcminute discrepancy led him eventually to ellipses Keplers Three Laws of Planetary Motion: Keplers 1 st Law The orbit of each planet about the Sun is an ellipse with the Sun at one focus. Keplers 2 nd Law As a planet moves around its orbit, it sweeps out equal areas in equal times. Keplers 3 rd Law More distant planets orbit the Sun at slower average speeds, obeying the precise mathematical relationship p 2 = a 3 ; p = orbital period in years and a = average distance from the sun in AU Newtons Three Laws of Motion: 1 st Law of Motion An object moves at constant velocity unless a net force acts to change its speed or direction. 2 nd Law of Motion Force = mass x acceleration 3 rd Law of Motion For any force, there is always an equal or opposite reaction force....
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This note was uploaded on 01/25/2012 for the course 750 110 taught by Professor Ericgawaiser during the Fall '10 term at Rutgers.

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