Jan_8 - From the Earth-centered to the Sun-centered Model...

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From the Earth-centered to the Sun-centered Model Tuesday, January 8
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For 2000 years, geocentric geocentric model for the universe was widely assumed. Spherical Earth at center of universe Moon, Sun, planets, Stars affixed to celestial sphere Dante, AD
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Most famous advocate of geocentric model: the astronomer Ptolemy Ptolemy (2nd century AD). Developed elaborate model to describe motion motion of stars, Sun, Moon, & planets.
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Stars: Stars: Circular motion around north celestial pole (near the North Star, Polaris) Time to complete circle = 23 hours, 56 min. = 1 sidereal day sidereal day
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Stars look as if as if they were glued to rigid spherical shell rotating once every 23 hr, 56 min. (You can’t tell, without a telescope, that some stars are closer than others.)
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Andromeda Galaxy: 2 million light-years away Comet Hale-Bopp: 10 light-minutes away No No sense sense of depth! of depth!
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Sun: Sun: Circular motion around celestial pole: part of circle is below horizon, so we say Sun “rises” and “sets”. Time to complete circle = 24 hours.
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Observed motions of the Sun: humanity’s first clock. 1
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Jan_8 - From the Earth-centered to the Sun-centered Model...

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