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ASTR 1101-001 Spring 2008

ASTR 1101-001 Spring 2008. Joel E. Tohline, Alumni Professor 247 Nicholson Hall [Slides from Lecture11]. Exam #1 Results. Total score composed of two parts: (g1) score on scale-model homework assignment is 25% (g2) score on in-class exam is 75% Where to find scores: g1 at bottom of exam

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ASTR 1101-001 Spring 2008

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  1. ASTR 1101-001Spring 2008 Joel E. Tohline, Alumni Professor 247 Nicholson Hall [Slides from Lecture11]

  2. Exam #1 Results • Total score composed of two parts: • (g1) score on scale-model homework assignment is 25% • (g2) score on in-class exam is 75% • Where to find scores: • g1 at bottom of exam • g2 at top-left of exam Example: g1 = 17/25; g2 = 23/27  grade = 25*g1 + 75*g2 = 89

  3. Contrasting Models of Planetary Motions • Greek Geocentric Model (Ptolemaic System) – §4-1 • Originated by Apollonius of Perga & Hipparchus in 2nd century B.C. • Expanded upon by Ptolemy in 2nd century A.D. • Copernican Heliocentric Model – §4-2 • Proposed in 1543 by Nicolaus Copernicus • (Also considered in 3rd century B.C. by Aristarchus)

  4. Contrasting Models of Planetary Motions • Geocentric Model • Underlying hypothesis: Earth is unmoving and at “center of the universe” • Heliocentric Model • Preferred (by Copernicus) initially because of its relative simplicity • Eventually proven correct by new observations made possible by the aid of telescopes (see Galileo’s discoveries §4-5)

  5. Observation/Explanation • OBSERVATION #1: Stars (and Sun, Moon, etc.) rise in east and set in west once every 24 hours • EXPLANATION (Ptolemy): Celestial sphere spinning east-to-west about a stationary Earth every 24 hours • EXPLANATION (Copernicus): Earth spins west-to-east once on its axis every 24 hours

  6. Observation/Explanation • OBSERVATION #2: Remove 24-hr diurnal motion; Sun and Moon both move steadily west-to-east at different rates (Moon = month period; Sun = year period) • EXPLANATION (Ptolemy): Sun and Moon both orbit the Earth • EXPLANATION (Copernicus): Moon orbits Earth (monthly) but Earth orbits Sun (yearly)

  7. Observation/Explanation • OBSERVATION #3: Superior planets [Mars, Jupiter, Saturn] usually wander slowly east-to-west (observed periods greater than 1 year) but periodically display retrograde (west-to-east) motion • EXPLANATION (Ptolemy): Planets orbit Earth via a combination of circular motions (deferent + epicycle) • EXPLANATION (Copernicus): Planets orbit the Sun at distances greater than 1 AU and with velocities less than the Earth’s

  8. Observation/Explanation • OBSERVATION #3: Superior planets [Mars, Jupiter, Saturn] usually wander slowly east-to-west (observed periods greater than 1 year) but periodically display retrograde (west-to-east) motion • EXPLANATION (Ptolemy): Planets orbit Earth via a combination of circular motions (deferent + epicycle) • EXPLANATION (Copernicus): Planets orbit the Sun at distances greater than 1 AU and with velocities less than the Earth’s

  9. Observation/Explanation • OBSERVATION #3: Superior planets [Mars, Jupiter, Saturn] usually wander slowly east-to-west (observed periods greater than 1 year) but periodically display retrograde (west-to-east) motion • EXPLANATION (Ptolemy): Planets orbit Earth via a combination of circular motions (deferent + epicycle) • EXPLANATION (Copernicus): Planets orbit the Sun at distances greater than 1 AU and with velocities less than the Earth’s

  10. Observation/Explanation • OBSERVATION #4: Inferior planets [Mercury, Venus] never wander very far (in angular separation) from the Sun; only seen shortly before or shortly after sunrise/sunset • EXPLANATION (Ptolemy): Planet deferents rotate together with the Sun • EXPLANATION (Copernicus): Planets orbit the Sun at distances less than 1 AU

  11. Observation/Explanation • OBSERVATION #4: Inferior planets [Mercury, Venus] never wander very far (in angular separation) from the Sun; only seen shortly before or shortly after sunrise/sunset • EXPLANATION (Ptolemy): Planet deferents rotate together with the Sun • EXPLANATION (Copernicus): Planets orbit the Sun at distances less than 1 AU

  12. Observation/Explanation • OBSERVATION #4: Inferior planets [Mercury, Venus] never wander very far (in angular separation) from the Sun; only seen shortly before or shortly after sunrise/sunset • EXPLANATION (Ptolemy): Planet deferents rotate together with the Sun • EXPLANATION (Copernicus): Planets orbit the Sun at distances less than 1 AU

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