"Letter to the Grand Duchess Christina of Tuscany (1615)" (abridged) by Galileo Galilei; Galileo Galilei, Karl Von Gebler, trans., in Galileo Galilei and the Roman Curia ()
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As to the arrangement of the parts of the universe, I hold the sun to be situated motionless in the center of the revolution of the celestial orbs while the earth revolves about the sun. They know also that I support this position not only by refuting the arguments of Ptolemy and Aristotle, but by producing many counter-arguments; in particular, some which relate to physical effects whose causes can perhaps be assigned in no other way.