ASTRO-110 Lecture Notes - Lecture 19: Ptolemy, Zodiac, Deferent And Epicycle
18 Sep 2020
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The geocentric system (ptolemy): that lasted for 2000 years. The greeks constructed a geo-centric (earth centered) model of the solar system. The geo-centric (or ptolemaic) model was constructed to explain (among other. In late 2009, mars moves across the constellations gemini and cancer. Mars"s things) the retrograde motion of the planets. Notice that the speed with which mars moves relative to the stars is not constant. March 1, 2010 mars seems to almost stop moving. From october 2011 through august 2012, mars will move across the zodiacal constellations cancer, leo, and virgo. Mars"s apparent motion will be direct (from west to east) most of the time but will be retrograde (from east to west) during february and march 2011. Notice that the speed of mars relative to the stars is not constant: the planet travels farther across the sky from october 1 to. December 1 than it does from december 1 to february 1.
