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  Copernicus delayed publication of his work for many years, though he circulated a few manuscripts. Some of his friends, including the cardinal of Capua and the bishop of Culm, encouraged him to publish, but he resisted. By 1539, the “evangelical” leader Martin Luther had heard of Copernicus's theory. There is a story that Luther complained, “The fool will overturn the whole art of astronomy.”19 But that claim was made by someone who did not hear Luther's words. Someone who did hear Luther firsthand reported instead that Luther said “the new astrologer” wished to turn astronomy upside down, while “I believe the Holy Scriptures, for Joshua commanded the Sun to stand still, and not the Earth.”20

  In 1541, the sixty-eight-year-old Copernicus finally agreed to publish his book, the labor of three decades. He dedicated it to Pope Paul III, expressing his prior fears of scorn and slander from “idle talkers wholly ignorant of mathematics,” those whose “inherent stupidity among philosophers holds as drones among bees.”21 Late in 1542, Copernicus suffered a stroke that paralyzed his right side. While he was convalescing, a Lutheran theologian who helped to oversee the printing of his book added an anonymous disclaimer, a foreword arguing that there is no certainty in astronomy and that hence the work consisted essentially of“hypotheses” convenient for mathematical calculations.22 Ill and confined to his bed, Copernicus finally received a copy of his book on 24 May 1543. He died a few hours later.

  The idea of Earth's motion was generally unwelcome. The “Reformed” Christian leader, John Calvin, denounced those who “pervert the order of nature. We shall see some who are so deranged, not only in religion but who show in all that they have a monstrous nature, that they say the sun does not move, and that it is the earth that moves and turns. When we see such persons, it must be said that the devil has possessed them.”23 Calvin was not necessarily referring to Copernicus, whom he might not have read, but to anyone who made such claims.

  The bestselling writer Arthur Koestler famously described On the Revolutions as “the book that nobody read,” but historian Owen Gingerich spent decades tracking copies of the book and concluded that Copernicus's work found plenty of readers. One was the prominent astronomer Erasmus Reinhold, who used it to calculate tables giving the positions of the heavenly bodies in time, which later served to revise the calendar. In his heavily annotated copy of Copernicus's book, Reinhold exulted, “Celestial motions are circular and uniform or composed of circular and uniform parts.”24

  Another who came to believe in the theory was the English mathematician Thomas Digges. In 1572, a bright new light was seen in the heavens. Digges inferred that it was a star, and he concluded that for ages astronomers had been wrong: the heavens were not unchanging. The region beneath the moon remained “the Empire of Death,” in his words, but there was change in the heavens, too. He thus thought it prudent to consider alternative accounts of the heavens, and so he adopted the “perfect description of the celestial orbs” which he attributed to the ancient Pythagoreans and to Copernicus.25

  Also in 1572, a Danish astronomer, Tycho Brahe, was likewise impressed by the bright new light in the heavens. Brahe was a wealthy nobleman who wore a lump of silver and gold in a hole in the center of his face, since a chunk of his nose, the bridge, had been cut off in a duel.26 This man with a golden nose devised instruments for measuring the positions of the stars and planets with great accuracy. And he found that the new bright light did not shift relative to the other stars, so it wasn't an atmospheric effect beneath the moon. It was indeed another star. Again, this meant that Aristotle had been wrong about the nature of the heavens.

  Since there was change in the heavens, as in Earth, then Earth might conceivably be in the heavens. Thomas Digges published a summary of the Copernican scheme in English, and he added the notion that the stars are not embedded in a sphere, but instead are spread throughout an infinite space beyond the planets. For Digges, the spherical and infinite orb of the stars was “the very court of coelestiall angels devoid of greefe and replenished with perfite endlesse joye the habitacle of the elect.”27

  If Earth were truly moving, astronomers expected to see some observable proof of this. So, throughout the years, Digges expected that the new star would become periodically brighter or dimmer as Earth presumably moved toward it or away from it. But no such effect was observed.

  Meanwhile, Catholic astronomers reformulated the calendar to fix the dates of religious events, such as Easter. In 1582, Pope Gregory XIII decreed that 4 October be followed immediately by 15 October, to bring the calendar into accord with the astronomical phenomena. Ten days were zapped out of existence. What happened on 5 October 1582? Nothing happened: that day did not exist (that is, in the few Catholic countries that immediately adopted the calendar, such as Italy and Spain). Tycho Brahe, a Lutheran, appreciated the value of the new Gregorian calendar.

  Like Copernicus, Brahe disliked some of Ptolemy's geometrical devices. Brahe appreciated the work of Copernicus, but only as a mathematical contrivance, he did not believe that Earth moves. Astronomers expected that if Earth moves, we should be able to observe some relative shifting of the stars: parallax. Copernicus knew that his hypothesis would entail parallax, but since no such effect was known, he had argued, like Aristarchus, that the stars were extraordinarily far away and far apart from one another. Apparently Brahe did not look for stellar parallax as a way to test Copernicus, but in 1583 he did try to detect parallax in the orbit of Mars, to test whether Mars is ever closer to Earth than Ptolemy expected.28 He found no such effect, so he rejected Earth's motion, which he also ridiculed as contrary to Scripture.

  But a few clergymen appreciated the idea of Earth's motion. In 1584, the Spanish theologian Diego de Zuñiga published a commentary on the book of Job, in which he noted that the characterization of God in Job 9:6 as “He who moves the Earth from its place, and its pillars are shaken,” seemed to say that Earth moves.29 Zuñiga claimed that this passage could be explained by “the opinion of the Pythagoreans” and of Copernicus. Seemingly contrary passages, such as Ecclesiastes 1:4, “Generations will come, and generations will pass away, but the Earth remains forever,” argued Zuñiga, referred not to any motion of Earth but to its durability.

  Meanwhile, Tycho Brahe also observed comets. According to Aristotle and Ptolemy, comets were not celestial phenomena, because comets exhibited change: they appeared and disappeared, and they did not travel in circles. So, astronomers and philosophers said that comets transpire beneath the orbit of the moon, as just another effect of Earth's atmosphere. But in 1577, Brahe observed a comet and carefully measured its parallax relative to the stars. He found that it exhibited too little parallax to lie beneath the orbit of the moon. He concluded that the comet was far above. This meant that Aristotle was mistaken: comets were not atmospheric phenomena. The ancient accounts turned out to be wrong—there could be change in the heavens along with noncircular motions.

  Some writers—who were not astronomers—had misconstrued Aristotle and Ptolemy, as if the ancient accounts claimed that the planets are embedded in crystalline material orbs, harder than diamond, “absolutely solid.”30 Brahe believed such misinterpretations. But by analyzing a comet in 1585, Christopher Rothman found that it traveled across the orbits of the planets, proving that no solid orbs separate them. In letters to Rothman, Brahe later appropriated this discovery to himself. He claimed to have refuted the common opinion of Pythagoras, Aristotle, and even Copernicus. Actually, there is no evidence that any of them ever held such an opinion about celestial orbs. Unfortunately, Brahe had little historical acumen, he “would not spare the time to scrutinize the writings of his predecessors to inquire who said what or when.”31 Accordingly, later historians wrongly echoed that the crystalline spheres were an ancient belief, propagating grandiose generalizations, reiterating mistakes.

  Since Brahe found inaccuracies in Ptolemy's theory, he formulated his own account of the heavens. The man with the golden nose argued that experience compels us to accept that Earth st
ays at the center of the universe while the moon, the sun, and the stars circle around it. And, he claimed, the planets circle the sun. Brahe's system made sense: it matched physical perceptions and it echoed some of the mathematical convenience of Copernicus's system. Brahe's system required the same phenomena entailed by the Copernican scheme, including a slight parallax for Mars. In 1587, Brahe detected that parallax and interpreted it as evidence in favor of his own system.

  In 1599, Brahe was appointed imperial mathematician to Emperor Rudolph II, in Prague, then-capital of the Holy Roman Empire. But Brahe died two years later, partly due to courtesy and gluttony. His assistant, Johannes Kepler, recounted Brahe's last days:

  On 13 October, Tycho Brahe dined with the illustrious Master Mincowitz, in the company of Mater Rosenberch. Holding his urine longer than usual, Brahe remained seated. He drank too much and felt pressure on his bladder but he valued civility. When he returned home, he could still barely urinate with the greatest pain, and nevertheless obstructed. The insomnia continued, with intense fever and gradually leading to delirium, and the food he ate, which could not be kept from him, exacerbated the evil…. On his last night, in his delirium, which was completely gentle, he repeated these words, like someone composing a verse: Not to seem to have lived in vain.32

  The man with the golden nose died on 24 October 1601. Thus ended the painstaking observations that he carried out and recorded for about thirty-eight years. Four centuries later, forensic analyses of hairs from Brahe's corpse showed that he had ingested toxic amounts of mercury, which caused or accelerated his illness and death.33

  Then, Brahe's collaborator, Kepler, became imperial mathematician, inheriting the planetary data. He was a German mathematician who was deeply religious. In the work of Copernicus, Kepler had found what he regarded as God's true design of the heavens.

  Years before Brahe's death, seeking to find the mathematical ordering of the universe, Kepler had investigated why there were only six planets, including Earth. He also wondered why the distances between the six planets had various definite sizes. Kepler had studied old writings that showed how Plato, and supposedly the early Pythagoreans, ascribed great importance to the five regular solids in the order of the universe. The regular solids are figures that are each made of only identical sides and each side has identical side-lengths: pyramid (four sides), cube (six sides), octahedron (eight sides), dodecahedron (twelve sides), and icosahedron (twenty sides). According to Proclus, Pythagoras had discovered “the structure of the cosmic figures,” though we have no evidence to support this.34 Impressed by such ideas, Kepler believed that he could explain the quantity of planets and their relative separations by inferring that their orbits were interspaced by the five regular solids.

  Consider a sphere, standing for the orbit of Saturn, and inside of it posit a cube, inside of which there would be another sphere, as large as can fit in the cube. That second sphere would be the orbit of Jupiter, and in turn, if a tetrahedron (a four-sided pyramid) were inscribed in that sphere, and another sphere were inscribed in the tetrahedron, the latter would give the orbit of Mars. Inside, there would be a dodecahedron, then the orbit of Earth, followed by an icosahedron, then the orbit of Venus, and finally an octahedron and in it the orbit of Mercury.

  Interspaced between the orbits of the six planets, the five regular solids in the sequence of six, four, twelve, twenty, eight, actually gave the relative separations between the planets. Kepler thought he had found evidence of God's divine plan of the universe.

  This geometrical scheme may seem ridiculous now. But it is remarkable in hindsight because it does replicate pretty closely the distances between the planets. Kepler published his Cosmographical Mystery in 1596. He had wanted to include an introductory chapter explaining the consistency of Copernicus's theory with the Bible, but the senate of the University of Tübingen requested that he omit that part. So Kepler quietly acquiesced: “We shall imitate the Pythagoreans also in their customs. If someone asks us for our opinion in private, then we wish to analyze our theory clearly for him. In public, though, we wish to be silent.”35

  Echoing some ancient writers, Kepler also alluded to the claim that Pythagoras could hear a universal harmony, a “music of the spheres” emitted by the motions of the planets.36 And if anything did not quite work in the supposed numerical and geometrical harmony of the universe, Kepler hoped that Pythagoras might perhaps rise from the dead to help him—which did not happen, he wrote, “unless perhaps his soul has transmigrated into me.”37

  In the meantime, Copernicus's conception had drawn the attention of a few other eccentrics. In particular, an Italian philosopher and priest, Giordano Bruno, shared similar views; he adopted and expanded the theory. Bruno despised the theory of epicycles, considering them mere crutches for Aristotle's erroneous theory.38 He claimed that no body is entirely spherical and that all natural motions deviate considerably from uniform circular motion around a center.39 Bruno denied the perfect circularity of celestial motions, claiming instead that planetary paths were more like spirals. He further reasoned that the stars are suns, that the universe is infinite, and that there exist other worlds like Earth. Centuries earlier, some Pythagoreans had allegedly claimed that the stars were worlds in the infinite space.40 Bruno studied texts that had been prohibited by the Catholic Church and attacked Aristotle's physics and his finite universe.

  Like the Pythagoreans, Bruno claimed that souls are repeatedly reborn, even into animals. Moreover, he entertained unorthodox ideas about Jesus Christ, whom he viewed as a clever magician: he doubted that Jesus was born from a virgin; he denied that Jesus was actually God. Bruno also behaved as if knowledge found by reason is superior to knowledge attained by faith. Because of such opinions, the Catholic Church prepared to put him on trial and excommunicate him. Bruno fled the Church and was excommunicated in absentia. He then befriended the Calvinists, but they too felt antagonized by him, and proceeded to arrest and excommunicate him. Bruno then approached the Lutheran Church, but since he argued that the various churches should coexist peacefully, the Lutherans excommunicated him in 1589. In 1592, he was taken out of his bed in the night by the Catholic Inquisition, who imprisoned him and put him on trial for years. Ultimately he refused to recant his theological and philosophical views, so they declared him guilty of heresy and sentenced him to death. On February 17, 1601, the officers of the Inquisition tied Bruno and conveyed him to the Campo dei Fiori, or Field of Flowers, where they silenced him with a gag on his tongue. Then they tied Bruno to a wooden stake, before onlookers, and burned him alive.

  Writers often claim that Bruno was executed because of his belief in Copernicus and in the infinity of worlds.41 Was Bruno a martyr for science? Actually, historians do not know for certain, because much of Bruno's file is missing from the records of the Inquisition. At least he was a martyr for the freedom of expression.

  Galileo Galilei was another Italian who adopted the Copernican scheme. In 1592 he became a professor of mathematics at the university of Padua, a position that Bruno had sought unsuccessfully. In 1609, Galileo learned that a Dutchman devised a spyglass to see distant things. So Galileo figured out how to construct and improve a telescope for seeing even farther, by grinding lenses designed according to the principles of optics. At the end of 1609, Galileo used his innovative telescope to observe several astonishing astronomical phenomena. In the words of one historian, “In about two months, December and January, he made more discoveries that changed the world than anyone has ever made before or since.”42

  In May 1610, Galileo published his observations in a book titled Message from the Stars. He described mountains on the moon and stated that the Milky Way consists of stars and that four shiny bodies orbit Jupiter. These findings were spectacular and lent support to the Copernican theory, which Galileo also believed had been the theory of Pythagoras.43 Copernicus had credited only the Pythagoreans; Galileo arbitrarily took an extra step.

  Galileo saw mountains and valleys on the moon
, which showed that, contrary to the beliefs of the Aristotelians, Ptolemy, and so many others, the moon was not a sphere. Therefore, the objects in the heavens were not all perfect. The moon resembled Earth—apparently it was another world. Since at least some heavenly bodies were like Earth, Earth too might be a heavenly body, as Copernicus seemed to require. Likewise, if the Milky Way indeed consisted of distant stars, then the universe would be much larger than most astronomers imagined.

  Galileo also saw that there were four lights wandering around Jupiter; hence, Jupiter was a center of heavenly motions. The bodies around it could be like the moon. Therefore Earth and Jupiter were alike, so Earth might be a planet. Moreover, Ptolemy's system was now wrong or incomplete: not all motion centered on Earth. If there were multiple centers of motion, then Earth might imaginably orbit the Sun. And further, Jupiter might well be another world.

  Earlier tradition alleged that some Pythagoreans believed that the moon was a world, like Earth, inhabited by large animals and beautiful plants.44 For years, Kepler had been drafting a story in which he dreamed of a journey to the moon. In the story, an old mother revealed to her son that she could converse with the moon and she showed him the secret art of conjuring spirits. Then an alien daemon quickly conveyed the boy and his mother on a dangerous voyage up to the moon to meet its inhabitants (who hid in caves), discuss their astronomy, and witness monstrous snakelike creatures that shun the sun and others who daily die by daylight and return to life at night.45

  Now Kepler heard of Galileo's findings. He immediately saw that they supported the Copernican outlook. Having learned that the moon really had mountains, Kepler inferred that, indeed, there were beings living on the moon! He speculated that they were large and spent their time building barriers with clay to protect themselves from the insufferable heat from the sun.46 But fascination was mixed with dread. At first, Kepler feared that the lights near Jupiter might actually be planets moving not around Jupiter but around a distant star. Kepler imagined life on Jupiter, but it seemed horrifying that the sun might not be the center of creation, that the countless stars might be other suns with many other worlds around them. He dreaded the views of Bruno.