# ASTR 1101-001 Spring 2008 Joel E. Tohline, Alumni

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 scalemodel 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 'Exam #1 Grades'

D's F's C's A's

B's Example: g1 = 17/25; g2 = 23/27 grade = 25*g1 + 75*g2 = 89 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) 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 Galileos discoveries 4-5) 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 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) 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 Earths

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 Earths

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 Earths 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 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

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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