ASTRONOMY 9: HISTORY OF COSMOLOGY

Handout #13

J. E. Baker
UC Berkeley, Spring 2000

Copernicus: A Reluctant Revolutionary

1.

Nicolas Copernicus (1473-1543, Poland)

• Moves Sun back to (well, near) center
• Revolutionary implications:
  • Earth is just another planet going round the sun
  • Demolishes Aristotelian spheres and walled-in medieval Christian universe
  • Universe becomes vast (lack of parallax)
  • Erases division of earthly vs. celestial realms
  • Aristotelian physics unsatisfactory: where is the center?
  • Breaks the close link between man, god, and universe
  • Loss of stability, rest, order
  • The Greeks did not discover all scientific knowledge
• Idea that our place in universe is not special: still called the Copernican Principle
• But these revolutionary ideas were not trumpeted (or even consciously recognized) by Copernicus! Merely implied by his work
• Heliocentric idea at first welcomed by relatively open-minded Church! Big trouble only decades after death of Copernicus, around 1600
• Copernicus was conservative, backward-looking, unwitting instigator of his revolution
• Last Aristotelian of the great scientists, at home in the medieval cosmos
• By standards of his day, Copernicus was a relic of an earlier world view!
  • Aristotelian physics long called into question by Bacon, Oresme, Cusa, ...
  • Aristarchus' heliocentric ideas never really forgotten, and were discussed openly prior to Copernicus
  • Winds of humanist Renaissance blowing from Italy, little effect on Copernicus despite his studies at Bologna
  • Still answering Plato's challenge to ``save the phenomena'', not trying to revolutionize cosmology
• Blind faith in ancient authority
  • Data mostly from Ptolemy
  • Only 27 recorded observations of his own, didn't bother to get modern instruments
  • Spent a lot of energy accounting for variation (not really there) in precession of equinoxes
• Other important revolutions going on
  • Luther's 95 Theses and Reformation
  • Invention of printing press--rise of vernacular
  • Journey of Columbus--Europe is not the center of the world?
• Caged in almost Pythagorean secrecy, little courage of conviction, plagued by doubts and fears of ridicule (but little threat of religious persecution)
• The Copernican system
  • Introduces even more epicylces than Ptolemy! (About 48 vs. 40)
  • No real observational improvement over Ptolemy
  • Only circular motions
  • Sun is displaced from center of orbits--as bad as the despised equants!
• Born of wealthy merchant parents, influenced by overbearing uncle Lucas and scandalous brother Andreas
• Studies some astronomy at Univ of Cracow (1490s)
• Studies Canon law at Bologna (1496)
• Studies medicine at Padua (1501)
• Cushy job as Canon of Frauenburg cathedral, few responsibilities
• Unsocial life largely spent locked away in lonely tower at Frauenburg
• Few human relationships: lived with housekeeper Anna Schillings until ordered by Church to get rid of her (Counter Reformation), one close friend (Giese), one disciple (Rheticus)
• Motivation for heliocentric idea: Ptolemy's equants not in accord with Aristotelian physics!
• Commentariolus (Little Commentary): preliminary announcement of heliocentric idea, manuscript only, 1510-1514
• Seven axioms:

  (a)

  Heavenly bodies do not all move round same center

  (b)

  Earth is center of moon's orbit and terrestrial gravity, but not universe

  (c)

  Sun is the center of the universe

  (d)

  Earth's distance from Sun much smaller than to stars

  (e)

  Earth's rotation causes daily rising and setting

  (f)

  Annual motion of Sun against fixed stars due to Earth's orbit

  (g)

  Retrograde motion also due to heliocentric orbits

• First Account: written by Rheticus, no mention of Copernicus by name, 1539
• On the Revolutions of the Heavenly Spheres, 1543, one of the worst-selling books in history!
• Not placed on Index of forbidden books for 73 years
• Copernicus delays publication for decades, finally gives in to pressure from Rheticus and Giese
• In dedication to Pope, Copernicus mentions Giese and others who influenced him, but not Rheticus!
• Rheticus demoted from Dean at Wittenburg to mere cushy Prof at Leipzig due to his homosexuality
• Leaves publication of Revolutions to pal Osiander
• Osiander views heliocentric idea as mere calculating hypothesis, does not believe in its truth
• Anonymously adds preface which goes too far in appeasing theologians: Copernicus merely ``saving the phenomena''
• Died of cerebral hemorrhage 1543, may have just seen published copy of Revolutions with Osiander's preface
• Hit on idea of ellipse for planetary motions, but for the wrong reasons and by faulty logic! Crossed out in manuscript
• Given Copernicus' trepidation and lack of originality and courage, why wasn't heliocentric model hit on earlier?
  • Physics wasn't there yet--deficiencies in Aristotle recognized, but no replacement yet
  • Copernicus was really interpreting Ptolemy, not nature; waste of time to humanist scientists
• Why does Copernicus get all the attention?
  • He systematized the heliocentric idea into a cosmological model (though one rooted in the past)
  • Writings attract notoriety (mostly heresay) at the right time

2.

Thomas Digges (1546-1595, England)

• Translated part of Copernicus' Revolutions
• Leader of English Copernicans
• Precise observations of Tycho's (1572) SN
• Lack of parallax implied very large distance
• Added a new idea to Copernican model: infinite space, with stars at varying distances

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