The History and Philosophyof Astronomy (Lecture 8: Copernicus)Instructor: Volker BrommTA: Jarrett JohnsonThe University of Texas at AustinAstronomy 350L (Fall 2006)Astronomy during the Renaissance (c. 1450 – 1600)• Rebirth of cultural activity in Europe!Intellectual Climate: Reformation (1517 onwards)• Restore lost original (pure) state of Church! Martin LutherIntellectual Climate: Humanism • Anti-Aristotelian strain, desire for classics! Erasmus of RotterdamPico della MirandolaIntellectual Climate: Neoplatonism• Search for underlying (mathematical) structureof reality! Marsilio Ficino• mathematical harmony• Sun worshipIntellectual Climate: Voyages of DiscoveryColumbus(1451-1506)Spanish and Portuguese exploration• New spirit of discovery!Intellectual Climate: Fall of Constantinople 1453• Escape of Greek scholars and texts to Italy!Intellectual Climate: Invention of Printing Press• Rapid dissemination of knowledge!Johannes GutenbergNicolausCopernicus • 1473 – 1543• De RevolutionibusOrbium Coelestium(1543, On the Revolutionof the Heavenly Spheres)• What was he:-first modern astronomer?- last ancient astronomer?NicolausCopernicus: Geography of his LifeCopernicus: Studies in Italy Bologna• Bologna and Padua: astronomy, mathematics, medicine, law• Eventually: Doctorate in church law (Ferrara)PaduaCopernicus: Canon at FromborkCathedral • Q: What is a canon?Copernicus: War in Varmia (1519-1521) • Poland vs Teutonic Knights, Copernicus involved in defenceCopernicus: De Revolutionibus(1543) • heliocentric model• Q: What motivated him?• Q: Structure of book?• Q: In which way was itrevolutionary?De Revolutionibus: Basic Structure • Book 1: Popular justification for Earth’s motion• Book 2-6: Mathematical details to account forcelestial (planetary) motions• Book 1: not original, not really convincing• Book 2-6: highly specialized(“Mathematics is for mathematicians”)De Revolutionibus: Basic Principles (Book 1) • Sun-centered• Earth is planet (3rd from Sun)•Earth’s motions:- daily rotation- annual revolution around Sun• Celestial motions uniform and circular• finite universeDe Revolutionibus: Basic Principles (Book 1) • daily rotation of celestial (fixed star) sphere• yearly motionof Sun alongecliptic (zodiac)Big Problem: Missing Stellar Parallax• Not observed (too small) until 1838 (Bessel)!Big Problem: Missing Stellar Parallax• Copernicus (correct) idea: Stars are at immensedistance (same idea as suggested by Aristarchus)• Copernican universe (although still finite) much larger than Ptolemaic oneDe Revolutionibus: Aesthetic Appeal PtolemyCopernicus• Conceptually simpler explanation for retrogrademotion (7 spheres vs 12)• Retrograde motion of planets natural outcome ofEarth’s motion!Copernicus vsPtolemy: Elongation of Venus • Observational fact: Venus and Mercury neverstray much (in angular distance) from Sun• Q: How to explain?Copernicus vsPtolemy: Elongation of Venus PtolemyCopernicus• Copernican system: Maximum elongationnatural consequence• Ptolemy: Need to make ad-hoc assumptionSunEarthVenusDe Revolutionibus: Final Result (Books 2-6) PtolemyCopernicus• As messy as Ptolemy, not more accurate:- a failure really (according to original claim)Principle of Perfect Uniformity• Same device as used by Arabs: Did he know?• eliminate un-Platonic equant with double epicycle!equantdouble-epicycleHarmony of Copernican System • No clear-cut proof possiblefor heliocentric model- actually: problem with missingfix-star parallax• But Copernicus claims thathis system is more elegant(“harmonious”) than Ptolemy’s, e.g.:- retrogression of planetary motion- ordering of planets- maximum elongation of Venus andMercury- correlation of opposition andbrightness (Mars, Jupiter, Saturn)De Revolutionibus: The Long Road to Publication • appeared in print 1543- year of Copernicus death• Q: Why did it take so long?• Commentariolus (basic ideas): - already ~1510• First (hand-written) draft:- already ~1530De Revolutionibus: Reasons for Procrastination • Copernicus was a busy man (canon, war,…)• He was afraid of ridicule because ofseemingly counter-intutive notion of Earth’s motion- attempt to perfectionize his new system• Anticipation of counter-reaction from Church - Earth’s motion contradicted by Scripture• Doubts whether he got it right:- it never quite fitsEnter Joachim Rheticus (1514-76)• professor of mathematicsin Wittenberg• visits Copernicus in Frauenburg• prods Copernicus toward publication• Narratio Prima(1540, first report):- summary of full De Rev.Early Reception of De RevolutionibusImportant Early Role of Wittenberg • Birthplace of Protestant Reformation! Martin Luther: 1517Enter Erasmus Reinhold (1511-53)• professor of astronomyin Wittenberg• uses De Rev. to calculatenew tables of celestial motions• Prutenic Tables (1551)widely used• Indirect fame for CopernicusCopernicus fame as “Second Ptolemy”Strasbourg Cathedral: Astronomical Clock (1574)Copernicus: Victory by Infiltration • Practical value of Reinhold’s Prutenic TablesEarly Reception: Need for better calendar (Pope Gregory XIII)• Uses De Revolutionibus!Copernicus: Victory by Infiltration • Astronomers got used to De Rev. as practicaltool for predicting celestial motions• Use despite, not because of, idea of Earth’s motion• Thus: De Rev. never went away (starting point forKepler and Galileo)• Copernicus in-built defence: Make book unreadablefor nonastronomers(“mathematics is for mathematicians”)•Osiander’s introduction: Heliocentric hypothesisjust convenient device of mathematical astronomy, not real!Copernican Revolution: A New Generation • Next generation of astronomers (Kepler, Galileo,…, Newton)• Address problems of New Astronomy(E.g., consequences of Earth’s motion…)• Copernicus addressed problems of