Islamic Innovators and Copernicus

Transcription

1 Islamic Innovators and Copernicus

2 Problems with Ptolemy Equant violates Plato s rule (uniform, circular motion) No absolute distances, i.e., not a physical picture of the cosmos Predicted change in lunar apparent size not observed (if mechanisms are real ) Ad hoc links of all models to Sun

3 Task of lecture Arabic and Latin medieval critiques of Ptolemaic astronomy Geocentrism vs heliocentrism not a simple choice from observations Does physics rule astronomy? How radical or novel was Copernicus? Problems with the Copernican heliocentric cosmos

4 Moving Earth stellar parallax? Earth Earth Sun Sun Geocentric Expect no parallax Heliocentric Expect parallax, not observed until 1837

5 Moving Earth Venus parallax? Earth S Parallax angle Venus E V S E V Geocentric Par (Ven) > Par (Sun) Heliocentric Par (Ven) > or < Par (Sun) Not observed until 1930s

6 Moving Earth birds left behind? r e = 6400 km Equator V equat = 1700 km/hr

7 Arabic astronomy, Islam and the need for astronomy Prayer Times Direction of Mecca Qibbla for mosques Typical astrological/medical concerns Court translations of Ptolemy, Aristotle Filosofa ( foreign philosophy) Large observatories and professionals

8 Arabic critiques of Ptolemy Improve predictive accuracy Correct Ptolemaic parameters with obs. Add trepidation to Ptolemy s precession Produce new tables to find positions (zijs) Fix the physics (hay a=real, physical cosmology in Platonic-Aristotelian tradition) Ibn al-haytham (d. 1040) defines hay a as a problem to be solved al-bitruji (1200) replaces epicycles & equants with homocentric spheres (model does not work) al-tusi (1250): replace equant with Tusi-Couple al-shatir (1350): replace equant with double epicycles

9 Tusi Couple 2a a Uniform circular motion makes linear harmonic motion!

10 Medieval Latin astronomy Scholastics synthesize Aristotle and Christian theology (Thomas Aquinas) Angels move celestial spheres Astrology accepted for everything but human will Medieval universities Trivium (grammar, logic, rhetoric) Quadrivium (astronomy, music, geometry, arithmetic) Attempted reforms in Latin West (Arabic influence)? Peurbach/Angelus & Tusi (1460)? Regiomontanus & homocentrism (1460)

11 Copernicus, the isolated canon Born in Torin, merchant s son Studied law, medicine in Cracow and Italy, acquired best Latin astronomy books in print Time of printing, Columbus, fall of Constaninople To Poland as Fromberg canon in 1503 The closet astronomer Observations begin 1503 Commentariolus, manuscript written ca De revolutionibus orbium coelestium [On the revolutions of the heavenly spheres], 1543 (Copernicus s only published book)

12 A Copernican Revolution? The traditional view Moving earth from Greeks (Philolaos, Heraclides) Explained solar links, retrograde motion naturally Osiander s instrumentalist preface Better predictive accuracy than Ptolemy New view: A conservative revolutionary Employed Tusi s mathematics to eliminate equant Sought hay a goal of restoring Plato s uniform, circular motion Predicted Ptolemy s positions, not improved accuracy But did add novel aesthetic considerations ( common measure ) Created problems for Aristotelian physics? Refuted by lack of observed stellar parallax?

13 Coeprnican advantages >>Explains retrograde as Earth passing outer planet >>Explains links of inner planets to Sun as their orbits around Sun

14 Steps to heliocentrism: 1 Sun Mars r R Earth Ptolemaic Superior Planet r = epicycle radius R = deferent radius

15 Steps to heliocentrism: 2 Sun Mars Earth Complete the parallelogram

16 Steps to heliocentrism: 3 Sun Mars Earth Add circle around Earth, circle around Sun = Tycho s model for Superior Planet

17 Steps to heliocentrism: 4 Sun Mars Earth Let Earth orbit Sun rather than Sun orbit Earth, i.e., shift from Tychonic to Copernican model

18 Steps to heliocentrism: 5 Copernican Sun r Earth Mars R r = Earth s distance = AU = common measure of solar system R = Mars distance From Ptolemy, R=60, r=39.5, thus R/r=1.52 or Mars is 1.52 AU from Sun!

19 Aesthetics of new cosmology in this arrangement we discover a marvelous commensurability [common measure] and an established harmonious linkage between the motion of the spheres and their sizes, such as can be found in no other way. De revolutionibus, Book 1 AU is common measure of planetary distances from Sun Planetary periods proportional to their distances from Sun Mer.24 yrs, Ven.62, Ear 1, Mars 1.9, Jup 11.9, Sat 29.4

20 Heliostatic not heliocentric! Earth Center of Earth s Orbit Sun Sun fixed Center of Earth s orbit moves Requires 3 circles

21 Copernican cosmology Eliminates equant with Tusi Couples (Arabic influence) Provides common measure for distances and harmonious linkage of period-distance Aesthetic contribution Heliostatic rather than heliocentric Retains small epicycles for each planet (not for retrograde motion) Same number of circles as Ptolemy Same format as Almagest Saves Ptolemy s predictions, not the heavens Creates crisis for Aristotle s physics What is the status of Copernican model (physical reality or astronomical hypothesis)?