Class Note for PTYS 206 at UA
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This 15 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Arizona taught by a professor in Fall. Since its upload, it has received 15 views.
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Date Created: 02/06/15
History of Theories for Motion of the Planets Ancients Thought planets orbited Earth geocentrism Copernicus Suggested that planets orbit Sun heliocentrism Brahe Tracked planets extremely carefully creating an amazing dataset Galileo Took telescopic observations that supported heliocentrism Kepler Using Brahe s data came up with 3 fundamental rules governing planetary motions Heliocentrism wins Geocentrism The view held until the mid 15003 All the planets as well as the Sun and Moon orbit Earth Each planet has an epicycle to explain retrograde motion But unsatisfying no prediction about relative locations of planet orbits No single nor simple relation governs how fast the epicycles rotate Each planet is a special case Celestial sphere rotates 0 the west Stars fixcd 0n celestial sphere b The Greek geocentric cosmogony H N Dtvcmhcr tru1 j H mm quotInn s r pldl39 cl I39d Ilnng cp39 Izpic C 39mnv s A c ward along dul39urulll A well mm Earth pluml muwx cu a rd rclrugmdc Inulium Heliocentrism Copernicus realized that if planets orbit the Sun retrograde motion is naturally explained The model allowed him to predict which planets were closer to the Sun and which were further He also realized that a trend exists planets that are further move slower and have longer periods This hinted at underlying simplicity and was more appealing than geocentrism But he couldn t grove geocentrism wrong Venus is never Far 39Fom he Sun The GeocewEric Modal exrlqineA L1is obsewa m as Fnllole Dc rcmulxun 5quotquot Ep dc or lnu d n 039u u mmc rare as chcnm nl39 Sunl Galileo Using telescope discovered that Venus has phases This proved geocentrism wrong He also discovered four moons around Jupiter proof that objects can orbit other celestial bodies This supported heliocentrism But circular orbits didn t quite fit the observations Brahe Took extremely careful observations of the positions of planets Phases o F Venus a 58 a 42 u 24quot u 1quotquot 110 Hehocenhism ensil exPlains bow 1116 fad Hm Venus Shays chase 0 We Su Venus Ms phases mama 9m New 0 Full lrcsccnl u 42quot Galileo discovered ka metfer has moons quot 39 I4 0 u 171 1 O HHC i C jTeSw r GWV VQHOM Pmm 620 Kepler Used Brahe s observations to deduce 3 fundamental laws of planetary motion 1 Planets orbit the sun and their orbits are ellipses rather than circles with the Sun at one focus heresy 2 A line joining a planet and the Sun sweeps out equal areas in equal times 3 The square of the siderial period of a planet is proportional to the cube of the semimajor axis of the orbit That is P2kA3 Major axis Minor axis mm 41 Rnym r mmymmummy v k A nmvwhl mu m n Inahw mm mm Mn N I nrw mrmhuuu
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