The Copernican Revolution

“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!)

Homework: Retrograde Motion & Epicycles

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.

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…

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

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

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

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