A More Perfect Heaven: How Copernicus Revolutionized the Cosmos - Dava Sobel (2011)
Part I. Prelude
Chapter 2. The Brief Sketch
The center of the earth is not the center of the universe, but only the center towards which heavy things move and the center of the lunar sphere.
—FROM THE Commentariolus, OR Brief Sketch,
BY COPERNICUS, CA. 1510
In 1510, when Copernicus, at thirty-seven, assumed his position in residence as a canon of Varmia in Frauenburg, the Cathedral Chapter assigned him a house, or curia, outside the fortification walls, plus two servants and three horses as perquisites of office. The influential chapter governed the lives of its member canons, as well as the residents of hamlets for hundreds of miles around, not to mention the numerous peasants who worked the thousands of acres of Church-owned lands that yielded the canons’ livelihood. Copernicus also took possession of his own designated altar in the cathedral nave. It was the fourth from the chancel, on the right—the one dedicated to St. Wenceslaus. Lacking Holy Orders, Copernicus could not celebrate Mass there himself, but then, neither could his brother or the majority of the other canons, who were also political appointees, not priests.
Copernicus encountered an ordained exception in Tiedemann Giese, a fellow canon seven years younger than he. Giese came from a well-known family in Danzig, where he had presided at the Church of Peter and Paul. He shared with Copernicus an abiding interest in astronomy, perhaps acquired when they befriended each other. Giese was almost certainly the first to hear Copernicus confess his secret knowledge of the cosmos. One imagines the priest’s initial reaction to those unorthodox ideas as skeptical at best, but in time he concurred, even encouraged Copernicus, and urged him to disseminate his theory.
By 1510, Copernicus had leapt to his Sun-centered conclusion via intuition and mathematics. No astronomical observations were required. He wrote out a short overview of his new heavenly arrangement, also probably in 1510, and sent it off to at least one correspondent beyond Varmia. That person in turn copied the document for further circulation, and presumably the new recipients did, too, because by May of 1514, when the Krakow physician and medical professor called Matthew of Miechow inventoried his private library, it contained “A manuscript of six leaves containing a Theorica [astronomy essay] in which the author asserts that the Earth moves while the Sun stands still.”
Copernicus had no idea that Aristarchus of Samos had proposed much the same thing in the third century B.C. The only work by Aristarchus known to Copernicus—a treatise called On the Sizes and Distances of the Sun and Moon—made no mention of a heliocentric plan. Copernicus stood alone, for the time being, on his moving Earth.
Tiedemann Giese, canon of Varmia.
The heavens challenge the astronomer, he noted in the opening paragraph of his Brief Sketch, to describe all the disparate motions of the divine bodies. His earliest predecessors in cosmology—here he saluted Calippus and Eudoxus from the fourth century B.C.—had embedded the Sun, Moon, and planets in a series of concentric spheres surrounding the Earth. The first astronomers envisioned these spheres as solid, invisible structures, each carrying a single planet. But these simple concentric spheres could not account for the planets’ periodic brightening in the sky, as though they were drawing nigh. Later sages favored eccentric spheres, with centers near but not at the Earth, to make up the difference in brightness, and they tipped each sphere’s axis at a slightly different angle, to allow the planets to bob up and down within the band of the zodiac. No single sphere, however, could embrace a planet’s periodic reversals in direction. Anyone who watched the wanderers night after night saw them now and again slow down, stop, then backtrack with respect to the background stars for weeks or months on end, only to stop and start up again the way they had gone before—fluctuating in brightness all the while. To accommodate this loop-the-loop behavior, some astronomers imagined the heavenly spheres as clearly defined lanes, within each of which a single planet reigned. Inside the sphere of Mars, for example, the planet rode around on one or more subsidiary spheres, called epicycles, whose combined motions accounted for its constantly changing position in the sky. The undisputed master of this balancing act, Claudius Ptolemy, flourished in Alexandria around A.D. 150.
Ptolemy coped so effectively with heavenly complexity in the second century that he remained the reigning authority in the sixteenth. By following Ptolemy’s instructions and using his tables, an astronomer could approximate the position of any planet at any time, past or future. As though to commemorate Ptolemy’s magnificent achievement, his book came to be called by the first word of its title in Arabic translation, Almagest—“The Greatest”—instead of the more modest Greek name the author gave it, Mathematike syntaxis, or “Mathematical Treatise.”
Copernicus revered Ptolemy as “that most outstanding of astronomers.” At the same time, he objected to the way Ptolemy violated the basic axiom of astronomy, which held that all planetary motions must be circular and uniform, or composed of circular and uniform parts. Ptolemy conformed his Earth-centered ideology with his accumulated data on planetary speeds and positions by allotting each heavenly sphere a so-called equant—in effect a second axis of rotation, off-center from the true axis. Although astronomers deemed it impossible for any sphere to rotate uniformly about an off-center axis, they overlooked the infelicity because Ptolemy’s technique worked on paper to give good predictive results. Copernicus’s mind, however, “shuddered” at the thought.
Clinging to a purer ideal, as he explained in the Brief Sketch, Copernicus had sought a new route to Ptolemy’s results, without committing Ptolemy’s crime of violating the principle of perfect circular motion. Along the way to his new solution, for reasons Copernicus chose not to elaborate, he had nudged the Earth from its accustomed resting place at the hub of the universe, to put the Sun there in its stead. He could well have restored the heavens to uniform circular motion without this drastic reordering of the heavenly bodies, but once the new configuration occurred to him, the configuration itself became paramount.
“All spheres surround the Sun as though it were in the middle of all of them, and therefore the center of the universe is near the Sun,” he wrote. “What appear to us as motions of the Sun arise not from its motion but from the motion of the Earth and our sphere, with which we revolve about the Sun like any other planet.”
THE HEAVENLY SPHERES
Each planet traveled in its own sphere, or region of the heavens. As depicted in this image from Theoricae novae planetarum, published in Nuremberg in the year of Copernicus’s birth, the sphere has a three-dimensional quality, high and wide enough to embrace a planet’s wanderings. Within the sphere, the principal path of the planet’s motion traces a thin circle centered on a point labeled c. deferentis. It is an eccentric circle, since the Earth (the center of the universe) is located at the point just below, c. mundi. The top label, c. aequantis, indicates the equant point, from which the planet’s motion appears uniform.
With a wave of his hand, he had made the Earth a planet and set it spinning. In fact he saw it propelled in three ways, on three circular routes. The first spirited the planet around the Sun every year. The second twirled it daily, producing the heavenly fireworks of sunrise, sunset, and what he called the “headlong whirl” of stars through the night. The third motion slowly wobbled the poles over the course of the year, to account for the direction of tilt for the Earth’s axis.
“Whatever motion appears in the sphere of the fixed stars belongs not to it but to the Earth,” he continued. “Thus the entire Earth, along with the nearby elements”—meaning the oceans and the air—“rotates with a daily motion on its fixed poles, while the sphere of the fixed stars remains immovable and the outermost heaven.”
Even Ptolemy had once conceded it might be easier in theory to let the Earth spin than to expect the whole firmament to wheel fully about every twenty-four hours—except that the idea of the Earth’s turning was “utterly ridiculous even to think of.”
As soon as Copernicus called for the Sun and the Earth to swap places, the planets snapped into a logical new order. They arrayed themselves outward from the Sun according to their speed of revolution, so that Mercury, long observed to be the fastest, was also the closest, followed by Venus, then Earth, Mars, Jupiter, and finally Saturn, the slowest. In the Earth-centric view, neither observation nor theory had ever settled the question as to which planet lay just past the Moon—whether Venus or Mercury—or whether the Sun orbited before, between, or beyond those two. Now he knew. Everything fit. No wonder the beauty of the system prevailed over the absurdity of the Earth’s motion. He hoped his own conviction would convince others to see the spheres his way, but offered no proofs at this point. He had decided, he said, “for the sake of brevity to leave the mathematical demonstrations out of this treatise, as they are intended for a larger book.” Then he proceeded to count and clarify all the individual planetary motions, arriving, in the final paragraph of the Commentariolus, at the grand total: “Mercury runs on seven circles in all; Venus on five; the earth on three, and round it the moon on four; finally Mars, Jupiter, and Saturn on five each. Altogether, therefore, thirty-four circles suffice to explain the entire structure of the universe and the entire ballet of the planets.”
Copernicus surely anticipated ridicule from his contemporaries. If the Earth rotated and revolved at great speed, they could argue, then anything not nailed down would go flying. Clouds and birds would be left behind. Moreover, his fellow astronomers could insist the Earth truly belonged at the center—not because humanity’s home deserved any special importance in the cosmic scheme, but because heavy, earthy things fell to rest there, and because change and death befell Earth’s inhabitants. The Earth represented the pit, not the pinnacle, of Creation. Therefore one dare not shove the Sun—“the lamp of Heaven,” as many called it—into the Hell hole at the center of the universe.
Several Islamic astronomers of the thirteenth and fourteenth centuries had found fault with Ptolemy for the same reasons Copernicus did. Nasir al-Din al-Tusi and Ibn al-Shatir, for example, managed to adjust Ptolemy’s circle violations without requiring the Earth to turn or abandon its central place. Copernicus used some of the same mathematical devices in his revision of Ptolemy, but reached his own singular conclusions about the Sun’s centrality, the Earth’s mobility, and the grandiose inflation of the cosmos required by his design.
If the Earth trekked all the way around the Sun, as he maintained, then two neighboring stars should appear now slightly closer together, now farther apart over the course of the year. Yet the stars never displayed any such displacement, or “parallax.” Copernicus got around the absence of parallax by supposing the stars too far away to reveal it. He increased their distance more than a hundredfold—so remote that the Earth-Sun separation shrank by comparison to the point of insignificance. “Compared to the great height of the sphere of the fixed stars,” he averred, “the distance between the Sun and the Earth is imperceptible.” The enormous chasm that suddenly yawned open between Saturn and the stars did not trouble Copernicus, as he had a ready explanation for it in the Creator’s omnipotence: “So vast, without any question, is the divine handiwork of the most excellent Almighty.” Beyond the periphery of the stars, God and His Angels hovered in the invisible heavens of the Empyrean.
After completing the Commentariolus around 1510, Copernicus began the slow work of elaborating his theory. The thirty-four circles of the planetary ballet now required exact design specifications, such as the radius of each one, its rate of rotation, and its spatial relationship to the other thirty-three. He could calculate many of these hundred-plus parameters using time-honored methods and tables. Then he would test the values by making his own observations.
The chapter, however, had other expectations of him.
In November 1510 Copernicus and fellow canon Fabian Luzjanski, who had studied with him in Bologna, went on an important mission to the chapter’s southern provinces. There they accepted the large sum of 238 marks—a full year’s revenue from the labor of peasants on Church land—for safe transport back to Frauenburg. Given that the Teutonic Knights were regularly and ruthlessly robbing the population of Varmia, the two couriers traversed the wooded, hundred-mile route home in constant danger of being waylaid and relieved of their cargo of coins. (Paper money had not yet come into circulation in Europe.) When they reached Frauenburg without incident, they distributed the funds among the canons according to custom.
The next November, in 1511, the chapter named Copernicus its chancellor, charged with overseeing the financial accounts and composing all official correspondence. The pace and volume of that correspondence quickened at the sudden death of his uncle the bishop on March 29, 1512. A week after Lukasz Watzenrode’s passing, the canons met on April 5 to elect his successor. They voted unanimously for their own Fabian Luzjanski—all except Luzjanski himself, who wrote another’s name on the ballot. The next day the canons gathered again and chose Tiedemann Giese to conduct the necessary confirmation negotiations with the Vatican. By June 1 the chapter needed two more spokesmen to contend against the king’s objections to their designated bishop. King Sigismund found no particular fault with Luzjanski; he simply preferred to install his own candidates in such positions. The Rome-Krakow-Varmia wrangle over the bishopric wore on through the summer and fall. On December 7, under a new agreement, Sigismund at last accepted Luzjanski, in exchange for the right of final approval over all future bishop selections. In addition, he insisted the entire chapter must pledge an oath of allegiance to the Crown, which they did on December 28, confident the king would honor, in return, his promise of royal protection.
Between Frauenburg and Rome—the northern and southern limits of his lifetime travel—Copernicus could see most of the same thousand stars that earlier astronomers of Egypt, Babylon, Greece, and Persia had observed. He measured each star’s celestial latitude and longitude to create a stellar catalog, which he published in On the Revolutions, Book II, chapter 14. He also tracked the positions of the planets against the background of the stars. With his wooden triquetrum, like the one pictured here, he could gauge a body’s altitude by sliding the hinged bar until its peepholes framed the planet or star, and then reading its elevation from the calibrated lower scale.
Only one canon failed to sign the new agreement and swear his loyalty to the Polish king. This was Copernicus’s brother, Andreas. The chapter had released him from all responsibilities in Frauenburg when he developed leprosy and, fearful of contagion, forced him to quit the region before Bishop Fabian’s formal investiture. They could not strip him of his canonry, which carried a lifetime tenure, but death would do that soon enough. Not even Doctor Nicolaus could cure the biblical curse of this painful and disfiguring disease. Already, eager contenders vied to become Andreas’s “coadjutor”—the person legally empowered to discharge his duties so long as he lived, and assume all his entitlements later, after his death. To a man, every canon could name some deserving relative qualified to fill this post. Naturally King Sigismund also had nominees in mind.
As Andreas left for Italy, in search of whatever solace he might find, Copernicus accepted a new line of duty as overseer of the chapter’s mill, bakery, and brewery. These establishments provided bread and beer to the canons—and also served the peasants, for the price of dues, which Copernicus would need to collect from them.
On March 31, 1513, according to the Varmia ledger of accounts, “Doctor Nicolaus has paid into the treasury of the Chapter for 800 bricks and a barrel of chlorinated lime from the Cathedral work-yard.” With these materials he built a level platform in a garden near his curia. By now he had traded the first residence he had been given for this new one, which must have been better situated for his purposes. The large paved patio, or “pavimentum,” as he called his construction, provided an unobstructed view of the sky and a solid footing for his astronomical instruments. He owned three with which he took the heavens’ measure: a triquetrum, a quadrant, and an armillary sphere. None of these devices contained lenses or sharpened his vision in any way. Rather, they functioned as surveyor’s tools, to help him map the stars and trace the paths of the Moon and planets.
In the spring of 1514, taking advantage of a redistribution of the chapter’s property, Copernicus purchased living quarters inside the cathedral complex. While holding fast to his estate and pavimentum on the outside, he paid 175 marks for a spacious, three-story tower at the northwest corner of the fortification wall, complete with kitchen and servant’s room. The top floor let in light through nine windows and gave out on a gallery, but he still preferred to observe from his patio platform. He stole hours from his sleep to stand watch out there, perched above 54° north latitude, on a forested hillside where the air hung heavy with mists off the Vistula Bay.
“The ancients had the advantage of a clearer sky,” he wrote in his own defense. “The Nile, so they say, does not exhale such misty vapors as those we get from the Vistula.” At the site of Ptolemy’s fabled observatory on the Nile, with its near-tropical climate, the planets climbed almost straight up from the horizon, instead of loitering along the tree line, and rode high in the sky, easily sighted through countless cloudless nights.
Everything Copernicus knew about Ptolemy when he prepared the Commentariolus, he learned from an abridged interpretation of Ptolemy’s work, called the Epitome of Ptolemy’s Almagest, published in Venice in 1496. Now, as he launched his own serious research project to revise astronomy, the full text of Ptolemy’s Almagest became available for the first time in a printed Latin translation. Copernicus consumed his copy, covering its margins with notes and diagrams.1
Copernicus found in the Almagest a model for the book he wanted to write, in which he would rebuild astronomy in a framework as impressive and enduring as Ptolemy’s. Meanwhile the Commentariolus, his prequel to On the Revolutions, was already making his name as an astronomer. This growing recognition no doubt accounted for the invitation Copernicus received from Rome to consult on calendar reform. The Julian calendar then in use, established by Julius Caesar in 45 B.C., had overestimated the length of the year by several minutes. Over time, the small founding error amounted to a gain of almost a day per century. Easter was on its way to becoming a summer holiday, and the Church’s other movable feasts were falling similarly out of step with the seasons. Therefore Pope Leo X, as part of his agenda for the Fifth Lateran Council, called on theologians and astronomers of all nations to help correct the flaw. Copernicus duly submitted his comments to Paul of Middleburg, the Bishop of Fossombrone, who coordinated the calendar effort for the duration of the council, from 1512 to 1517. The bishop listed the contribution from the Polish canon in his official report. Unfortunately he did not describe even the gist of Copernicus’s suggestion, and later, even more unfortunately, Copernicus’s original letter was lost.