ASTR 100 Lecture Notes - Lecture 4: Retrograde And Prograde Motion, Geocentric Model, Ellipse
26 Sep 2016
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Document Summary
Planets and the zodiac the planets do not follow the same cycle behavior of the stars. They move relative to the stars in a very narrow band centered about the ecliptic and called the zodiac. Occasionally a planet will move from east to west relative to the stars. Explaining retrograde motion was one of the one of the main reasons astronomers ultimately rejected the idea of the earth being the center of the solar system. Heliocentric models explain retrograde motion as a natural consequence of two planets passing each other. Copernicus could derive the relative distance of planets from the sun and explain why venus and mercury were always close to each other. Problems: could not predict planet positions any more accurately than the model of. Could not explain lack of parallax motion of stars. Designed and built instruments of far greater accuracy that any yet devised.
