The History and Philosophyof Astronomy (Lecture 5: Middle Ages II)Instructor: Volker BrommTA: Amanda BauerThe University of Texas at AustinAstronomy 350L (Spring 2005)Medieval Astronomy and Cosmology• Middle Ages I (Jan. 27)- Decline of Western (Mediteranean) Civilization- Early Middle Ages (“Dark Ages”): 500 – 1000 AD- Ascendancy of Islamic Astronomy (800 – 1400 AD)- Preservation and transformation of ancient knowledge• Middle Ages II (Feb. 1)- Recovery of European Civilization- High and Late Middle Ages (c. 1000 – 1450 AD)- Setting the Stage for the Copernican Revolution - Recasting of the Ancient TraditionEurope Recovers: Later Middle Ages (c. 1000 – 1450)• Romanesque: e.g., Dome in Speyer (1030-1061)• Gothic: e.g., Chartres cathedral (1145-1220)Europe Recovers: Later Middle Ages (c. 1000 – 1450)• Art in the Age of ChivalryEurope Recovers: New Spirit of ExplorationMarco Polo(1254-1324)Journey to China: 1271-95Rediscovery of Ancient Knowledge: Arabic Transmission • multiple sources: e.g., Spain, CrusadesRediscovery of Ancient Knowledge: - via Moorish Spain• Translations:Arabic Latin• Later: directlyGreek Latin• Transfer of know-how:- computation- astrolabesAlhambra, GranadaRediscovery of Ancient Knowledge: - via CrusadesSiege of Antioch, 1098 AD• Europe becomes aware of high level of IslamiccivilizationRediscovery of Ancient Knowledge: Emergence of the UniversityOxford University• Universities: A European Invention (12thand 13thcent.)• Objective: Understand ancient, rediscovered texts!Structure of Medieval University Seven liberal Arts (Septes Artes Liberales): TriviumLogic (Dialectic)GrammarRhetoricStructure of Medieval University Seven liberal Arts (Septes Artes Liberales): QuadriviumarithmeticgeometrymusicastronomyScholasticism: inconsistencies in ancient astronomy • Aristotle and Ptolemy:- 500 years apart in real time- scholastics rediscover it at same instant Fiction of unified body of “ancient wisdom”• But: two systems are inconsistent!- Aristotelian concentric spheres vsPtolemy’s deferent/epicycle system- Aristotle wants to explain real mechanism behindplanetary motion (“physics’)- Ptolemy (“mathematical astronomy”) wantsto predict motions, but does not claim that planetsreally move according to his constructions!Adopting Ptolemy’s Almagest: Sacrobosco• John of Holywood (d. 1256)Sacrobosco• taught in Paris• wrote De Sphaera (Sphere)• standard textbook for 400 yrs• simplified version of AlmagestThe Christian Universe: Thomas Aquinas • St. Thomas (1225-74)• Dominican monk• Reconciled Aristotlewith Christian Theology• Summa TheologiaeThe Christian Universe: Thomas Aquinas Aristotelian cosmologyChristian cosmologyThe Christian Universe: Dante’s Divine Comedy• Astronomy = Theology• Central Earth becomesessential ingredient ofChristian TheologyThe Empyrean: Dante and Beatrice behold ParadiseScholastic Critique of Aristotle: Motion of Projectile (Impetus Theory)Buridan’s Ass• Jean Buridan (14thcent.)• taught in Paris• member of Nominalists• Buridan’s ass: The Tyranny of ChoiceProjectile Motion: Aristotle’s Theory• Basic principle: heavy bodies (elements earth or water) are at rest or move straight to center of Earth (= center of universe)sling???airpush• To deviate from Aristoteliannatural motion: need externalinfluence!• For projectile: influence comes from pushed-aside air bubble!Center ofuniverseProjectile Motion: Buridan’s Theory• Basic principle: heavy bodies are at rest or continue to move according to impetus initially imparted to them slingimpetusgravity• impetus = (modern) momentum (Galileo, Newton)(mass x speed)• crucial step in allowing Earth to move!Scholastic Critique of Aristotle: Demonstrating Possibility of Earth’s MotionNicole Oresme• Nicole Oresme (14thcent.)• taught in Paris• pupil of Buridan• demonstrates logicalpossibility of Earth’s motionMotion of Earth is possible: Nicole Oresme• Idea 1: Earth could move in circles around center of universe!then Earth would be a planet, one among many!Q: What would happen? center ofuniverse1stEarth2ndEarthAristotle:Two Earth’s would collide:Earth is unique!Motion of Earth is possible: Nicole Oresme• Idea 1: Earth could move in circles around center of universe!then Earth would be a planet, one among many!Q: What would happen? 1stEarth2ndEarthOresme:Each heavy body (e.g., planet) has its own center of attraction: Earth could be a planet!two differentcenters of gravity!Aristotelian Argument against Earth’s Rotation: Aristotle argued: Stone would be left behind if Earthrotated! Stone/arrowObserver• Basic principle: heavy bodies follow natural motiontowards center of Earth = cent. of universeOresme’s Argument for Earth’s Rotation: Oresme argued: Stone would not be left behind if Earth rotated! Stone/arrowObserver• Basic principle: impetus theory!- stone or arrow has sideways impetus stone follows EarthNo rotation:With rotation:Oresme’s Argument for Earth’s Rotation: - Optical relativity: both models can explain appearance• two equivalent ways to understand daily motionof fixed stars! Fixed starsEarthA: Earth rotates!B: Fixed stars rotate!A Universe without limit: Nicolaus of Cusa• Cusanus (1401-64 AD)• lived in Southern Germany• was a Cardinal ofRoman Catholic Church• Of Learned Ignorance(De Docta Ignorantia)A Universe without limit: Nicolaus of Cusa• Basic principle: Opposites coincide (become the same)in the process of going to infinity (coincidential oppositorum)- E.g., curve and straight line• But also: Center and circumference- Coincide in the limit of the absolute smallest• The realm of the absolute is God!- material universe cannot attain this!Universe has no center and no edge!Astronomy in the Middle Ages (Scholastic Period)• Rebirth of intellectual, scientific activity• Rediscovery of ancient texts (via Arabic transmission)• Founding of Universities (Scholastic Philosophy)• Recasting of tradition at Dawn of Copernican Revol.:- Aristotelian-Ptolemaic system incorporated into Christian theology opposes Copernicus!- New theory of motion establishes plausibilty ofEarth’s motion crucial precondition for