AST—Jan 12 Lecture + Chapter Notes

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Astronomy & Astrophysics
Michael Reid

ASTThe History of the Cosmos Thursday January 12 201233The Copernican Revolution y Copernicuss workoverturned the Earthcentered Ptolemaic model y Copernican Revolutionled to the development of all modern science and technology How did Copernicus Tycho and Kepler challenge the EarthCentered model Nicholas Copernicusy Wealthy family y Began studying astronomy in late teens y Discovered simple geometric relationships that allowed him to calculate each planets orbital period around the sun and its relative distance from the sun in terms of the EarthSun distance o Was convinced the Suncentered idea must be correct y BookConcerning the Revolutions of the Heavenly Spheres y Problem believed that motion must occur in perfect circlesincorrect assumption forced him to add numerous complexities to his system circles on circles to get it to make decent predictions o Was no more accurate than the Ptolemaic model Tycho Brahey Kept his passion secret y Observed what he called nova meaning new star o Proved that the nova was much farther away than the moon o Today we call that supernovaexplosion of a distant star y Made similar observations of a cometsmall object that orbits a star o Proved that it too lay farther away than the moon y Tychos data remain the best set of nakedeye observationsaccurate to within a 1 acrminute thickness of a fingernaily Model o Earth must remain stationary o Sun orbits the Earth while all other planets orbit the SunJohannes Keppler y Was hired by Tycho y Religious and believed that understanding geometry of the heavens would bring him closer to God y Abandoned the idea of circular orbits y Key discover planetary orbits are not circles but instead area a special type of oval called an ellipseTwo points on the circle tacks y Focihalfaxis of ellipse y Major Axis long axis of ellipseSemimajor Axisy Eccentricity describes how much an ellipse is stretched out compared to a perfect circle
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