ASTRON 1F03 Lecture Notes - Lecture 1: Galilean Moons, Deferent And Epicycle, Microsoft Onenote
17 Sep 2019
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The motion of the planets: the sun and moon move simply, the planets wander on the sky along the ecliptic, mostly, west to east, occasionally they loop back retrograde motion. Geocentric system: aristotle advocated a geocentric system( everything revolves around the earth, he insisted that all orbits must be circles based on the innate perfection of spheres. Retrograde motion and epicycles: to get the planets to appear to go backwards, epicycles (or more smaller circles were needed, recall that the data was poor. Inferred by looking at the sky with the naked eye. No parallax seen(could not detect the motion of the earth) The pinnacle of epicycles: ptolemy: attempted to fit all observations to date, required 80 circles and the centers of the large circles were offset from earth slightly, not a simple theory(occam"s rasor, failed to pass future theory. Moon is not a perfect sphere but similar to earth. Not a perfect sphere, has dark regions called sunspots.
