1. The Copernican Revolution

2. “Strange” motion of the Planets
Note: outer planets are slower
Planets usually move from W to E relative to the stars, but sometimes strangely turn around in a loop, the so called retrograde motion (Explanation: next lecture!)

3. Homework: Retrograde Motion & Epicycles

4. Ptolemy (~140 AD) Puts forth a complete geocentric model
dominates scientific thought during the Middle Ages
Longest lasting (wrong) theory ever: 1000yrs
Major Work: Almagest
Had known flaws, e.g. the moon followed a path that brought it closer/farther from the earth. But the apparent size of the moon was roughly constant.

5. Epicycles Ptolemy’s explanation of retrograde motion
About 40(!) epicycles necessary to explain all observations complicated theory
After Ptolemy the only significant observations were made by the Arabs – provided continuity between ancient scholarship and that of the Renaissance
Polynesians, Mayans…

6. The Medieval Setting Dominant Church 1000 years of relative stagnation
Experimental research greatly reduced
To answer a question:
“Study the Bible or Aristotle!”

7. The Renaissance Setting
Invention of the print (1450) by Gutenberg
Books widely available!
(Think: Manuscripts vs Amazon.com)
End of Middle Age Church Domination
Back to the roots (renaissance=rebirth)
Study of Arabic astronomers
Intellectual movement

8. Nicolas Copernicus (1473–1543)
Rediscovers the heliocentric model of Aristarchus  BOOKS!
Planets on circles
needs 48(!) epicycles to explain
different speeds of planets
Not more accurate than Ptolemy
Major Work : De Revolutionibus Orbium Celestium
(published posthumously)
Published De Revolutionibus Orbium Celestium only posthumously
Unsigned preface by Andreas Osiander meant to reassure ecclesiastical authorities that divine revelation was the sole source of truth
May have subscribed to a sort of neo-Platonic sun worship (a “visible god”)
GIORDANO BRUNO (Italian; 1548) proposes that the Sun is just one star out of an infinite number. Similarly, God gives each of us an inner source of power equal to that of others. In 1600, Bruno was burnt at the stake for heresy

9. Copernicus’ heliocentric Explanation of retrograde planetary motion
See also: SkyGazer