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Chapter 4

ASTR 1101 The Solar System Chapter 4.docx

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Louisiana State University
ASTR 1101

Chapter 4Motions of the PlanetsGeocentric model Earth is center of everything Everything orbits usAristotle built and used for centuriesatomic modelPrograde motion movement in the normal directionRetrograde motion moving backwardsEx of mars in 2003Geocentric model cannot explain this phenomenon Can do loops or zig zagsEpicycle around a deferentWas used for 1200 yearsTo fix itEverything still orbits the earthNow everything still on epicycles that slide on deferentslook on slides of geocentric model used for 1200 yearsdeferent movement around the earthepicycle the spinning of the planet on the epicycleCopernicusbelieved that the geocentric model shown motions that were too complicated to be realitygeocentric model does not explain retrograde motionbuild the first mathematical heliocentric systemwanted perfectly circular orbits Couldnt fix why some planets moved faster than othersHeliocentric Modelinferior planets planets who are closer than the sun than uslie within the earths orbitmercury and venushave 4 positions of interestinferior conjunction conjunctionplanetsun are ina linesuperior conjunctionplanet in line with sun but farthest away it can gettwo on outsides greatest eastern elongation greatest western elongationjust means east and west of sunto observe the eastern look sundownto observe western look sun risegreatest distance between planet and sun it can besuperior planets outside the earth orbitonly two positions of interestconjunction planets on opposite side of sunopposition plants on opposite side of earth from the sundo not go through a full set of phases like with inferiorthis helps explain the retrograde of mars bc mars has longer way to travel around the sun earth is inferior so earth catches up and passes mars Therefore mars appears to be in retrogradeheliocentric model contCopernicus insisted that the heavens were perfect therefore the planets
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