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Cosmogony

Models of the Solar System, Gravitation and the motion of the Planets – A.K.A DEAD WHITE GUYS WEEK! HW #4 – Kepler’s Laws is available now on Mastering Astronomy , Due Thursday 21 st of September. Cosmogony. A cosmogony is theory about ones place in the universe.

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Cosmogony

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  1. Models of the Solar System, Gravitation and the motion of the Planets – A.K.ADEAD WHITE GUYS WEEK!HW #4 – Kepler’s Laws is available now on Mastering Astronomy, Due Thursday 21st of September

  2. Cosmogony • A cosmogony is theory about ones place in the universe. • A geocentric cosmogony is a theory that proposes Earth to be at the center of the universe. • A heliocentric cosmogony is a theory that proposes the Sun to be at the center of the universe.

  3. geocentric (Earth-centered) heliocentric (Sun-centered) Which is the geocentric cosmogony and which is the heliocentric cosmogony?

  4. Pythagorean Universe • time: about 550 bc • first recorded attempt at rational explanation of heavens • formed foundation for Greek astronomy

  5. Philosophical Ideas • The heavens represent perfection. • The heavens are immutable. • The circle is the perfect shape. • All heavenly motions must be circular.

  6. Pythagorean Model • stars reside on stellar sphere • stellar sphere rotates about axis in 23 hours 56 minutes • Sun follows path called ecliptic going around Earth once in one year • accounts for most observations!!

  7. North Star Stellar Sphere Axis of Rotation How the Greeks modeled the heavens

  8. Polaris NORTHERN HORIZON

  9. BUT - THERE WAS A COMPLICATION …. • There were stars that appeared to move across the sky without staying in their respective constellations • WANDERING STARS • (Greek word for wanderer is planete`)

  10. Prograde and Retrograde Motion • Prograde Motion(normal motion) – The apparent West to East motion of objects (over many nights) as compared to the stationary background stars. • Retrograde Motion - The apparent East to West motion of objects (over many nights) as compared to the stationary background stars.

  11. Planets were often called wandering stars because they seem to slowly move from one constellation to the next. West East South

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