Free Coming of Age in the Milky Way by Timothy Ferris

spheres—although, like Aristotle, Copernicus never could decide whether the spheres actually existed or were but a useful abstraction.
    Copernicus also read Plato, as well as many of the Neoplatonic philosophers whose work ornaments and obfuscates medieval thought, and from them absorbed the Platonic conviction that there must be a simple underlying structure to the universe. It was just this unitary beauty that the Ptolemaic cosmology lacked. “A system of this sort seemed neither sufficiently absolute nor sufficiently pleasing to the mind,” Copernicus wrote. 3 He was after a grasp of the more central truth. He called it “the principal thing—namely the shape of the universe and the unchangeable symmetry of its parts.” 4
    Rather early on, perhaps during his student days in sunny Italy, Copernicus decided that the “principal thing” was to place the sun at the center of the universe. He may have drawn encouragement from reading, in Plutarch’s
Morals
, that Aristarchus of Samos “supposed that the heavens remained immobile and that the earth moved through an oblique circle, at the same time turning about its own axis.” 5 (He mentions Aristarchus in
De Revolutionibus
, though not in this context.) Possibly he encountered more recent speculations about the motion of the earth, as in Nicole Oresme, the fourteenth-century Parisian scholar who pointed out that
    if a man in the heavens, moved and carried along by their daily motion, could see the earth distinctly and its mountains, valleys,rivers, cities, and castles, it would appear to him that the earth was moving in daily motion, just as to us on earth it seems as though the heavens are moving…. One could then believe that the earth moves and not the heavens. 6
     
    Copernicus was influenced by Neoplatonic sun worship as well. This was a popular view at the time—even Christ was being modeled by Renaissance painters on busts of Apollo the sun god—and decades later, back in the rainy north, Copernicus remained effusive on the subject of the sun. * In
De Revolutionibus
he invokes the authority of none other than Hermes Trismegistus, “the thrice-great Hermes,” a fantastical figure in astrology and alchemy who had become the patron saint of the new sun-worshipers: “Trismegistus calls [the sun] a ‘visible god,’ Sophocles’ Electra, ‘that which gazes upon all things.’” 7 He quotes the Neoplatonist mystic Marsilio Ficino’s declaration that “the sun can signify God himself to you, and who shall dare to say the sun is false?” 8 Finally, Copernicus tries his hand at a solar paean of his own:
    In this most beautiful temple, who would place this lamp in another or better position than that from which it can light up everything at the same time? For the sun is not inappropriately called by some people the lantern of the universe, its mind by others, and its ruler by still others. 9
     
    Trouble arose not in the incentive for the Copernican cosmology, but in its execution. (The devil, like God, is in the details.) When Copernicus, after considerable toil, managed to complete a fully realized model of the universe based upon the heliocentric hypothesis—the model set forth, eventually, in
De Revolutionibus
—he found that it worked little better than the Ptolemaic model. One difficulty was that Copernicus, like Aristotle and Eudoxus before him, was enthralled by the Platonic beauty of the sphere—“The sphere,” he wrote, echoing Plato, “is the most perfect… the most capacious of figures … wherein neither beginning nor end can be found” 10 —and he assumed, accordingly, that the planets move incircular orbits at constant velocities. Actually, as Kepler would establish, the orbits of the planets are elliptical, and planets move more rapidly when close to the sun than when distant from it. Nor was the Copernican universe less intricate than Ptolemy’s: Copernicus found it necessary to introduce Ptolemaic epicycles into his model and to