A More Perfect Heaven (29 page)

Tycho took his homeland’s far northern latitudes (worse than those bemoaned by Copernicus) as a proud birthright, and dedicated an early work to King Frederick of Denmark. While Tycho did allow that the extreme cold of the climate could disturb an astronomer’s serenity, it seems never to have deterred him. Five years after his nova discovery, in the early dark of another November night, Tycho stood fishing at a pond when a comet appeared to him. Its bright bluishwhite head and long ruddy tail—like a flame seen through smoke, he said—persisted through autumn into winter. That lengthy visitation gave Tycho time to prove that comets, though generally assumed to be quirks of the Earth’s atmosphere, actually traced paths among the planets. In contrast to contemporaries who feared the comet augured famine and pestilence, maybe even the death of a leader, Tycho confined its wrath to the heavens themselves. The Great Comet of 1577 condemned the ancient notion that solid celestial spheres carried the planets on their eternal rounds. Tycho saw plainly that no such structures impeded the comet’s free travel, and therefore concluded that no such structures existed. When he delivered this thunderbolt, one could almost hear the tinkle of shattering crystal.
⁵

Tycho Brahe, Lord of Uraniborg.

Tycho’s admittedly nonacademic achievements soon gained him an adjunct faculty position at the University of Copenhagen, where he lectured briefly on Copernicus’s ideas and distributed the
Prutenic Tables
to his students. In addition to having read
On the Revolutions
, Tycho also acquired a handwritten copy of the
Brief Sketch
from a friend who had known Rheticus. Recognizing the mathematical importance of the document, Tycho made additional copies to distribute among other mathematicians, though he refused to accept the reality of the Earth’s motion. Bold as he was, and openly admiring of Copernicus, he stood firm on the stationary Earth. For, if the Earth truly pursued a great circle around the Sun, Tycho reasoned, then an Earthly observer would see the spaces between certain stars widen and narrow over the course of the year. He estimated the expected change, called parallax, at 7°, or about fifteen times the diameter of the full Moon. Tycho’s failure to perceive any parallax, even a tiny one, convinced him that no Earthly revolution took place. Copernicus’s explanation—that the stars’ tremendous distance precluded the perception of parallax—rang hollow to Tycho. Why, he asked, should the distance to the stars mushroom from Ptolemy’s ten thousand Earth diameters to the several million required by Copernicus? What purpose would all that emptiness serve? What’s more, stars visible across such immense gulfs would need to be absurdly large, perhaps bigger than the entire expanse of Copernicus’s great circle. Incredulous, Tycho sought alternative means to realize the best of Copernicus’s ideas without moving the Earth, and came up with the compromise that bears his name. In the Tychonic system, Mercury, Venus, Mars, Jupiter, and Saturn all orbit the Sun, while the Sun, in turn, carries them along as it orbits the central, immobile Earth.

In order to prove the superiority of his system, published in 1588, over the Ptolemaic or the Copernican, Tycho needed reliable data—such data as had never before been available—regarding the planets’ motions. He single-handedly set new standards for accuracy and precision in observation, first by expanding the sizes of his custommade instruments to giant proportions. In place of a handheld cross-staff or pair of compasses, for example, Tycho substituted a mammoth quadrant that stood twenty feet high and required a crew of servants to operate. Later he fashioned other devices—still grand but not quite so unwieldy—that yielded good readings on large, legible scales, where each degree of arc divided into its full complement of sixty minutes (and in some cases further subdivided into multiples of arc-seconds). With the cooperation of his prestigious family, he built his country’s first astronomical observatory. King Frederick then provided the land and funding for a second one, equipped with more and still grander tools of Tycho’s design, which proved, by all accounts, the finest instruments in the world for pinpointing planetary positions. Both Tycho and his magnificent observatory, Uraniborg, on the island of Hven, drew income from canonries and other Church benefices assigned to them by the king. Here Tycho ruled a staff of talented assistants, a workforce of disgruntled peasants, and the whole of the night sky for more than twenty years.

THE TYCHONIC SYSTEM
Tycho set the planets in orbit around the Sun, but left the Earth immobile at the center of the universe. Although Tycho’s observations demonstrated the heavens’ solid spheres to be a fiction, Tycho could not bring himself to believe the Earth rotated and revolved.

After Frederick died, Tycho fell out of favor with Christian, the heir to the Danish throne, and felt forced to abandon Uraniborg. The search for a new patron led him to Prague in 1599, to the court of the Holy Roman Emperor, Rudolf II. Although Catholic, Rudolf acted liberally toward Lutherans in general, and smiled with special warmth on one so skilled in the art of astrology as Tycho Brahe. The emperor gave him his choice of castles and put him to work prognosticating affairs of state.

The move to Prague also put Tycho in proximity to Johannes Kepler, thereby facilitating their fateful collaboration. Kepler, not yet well known to most astronomers and living in modest circumstances, could never have afforded a visit to Tycho’s island. He welcomed Tycho’s presence in Bohemia as an act of God. By further provision of Providence, Kepler found Tycho’s chief assistant engaged in Mars studies when he joined the team at Benatky Castle in the spring of 1600.
“I consider it a divine decree,”
reflected Kepler, “that I came at exactly the time when he was intent upon Mars, whose motions provide the only possible access to the hidden secrets of astronomy.”

Kepler had been an infant in arms in Weil der Stadt in southwest Germany the year of Tycho’s nova, but when he was five, his mother took his hand and led him up a hill outside town to see the Great Comet of 1577. By then, Kepler’s eyesight had already begun to fail him. Likewise the noble standing that once elevated the Kepler family name had eroded before his birth, so that the myopic young genius inherited little more than a coat of arms. By dint of his intellect, however, he won scholarships that carried him all the way through seminary and university. He focused his self-professed
“burning eagerness”
on studies of astronomy that convinced him of the correctness of the Copernican hypothesis.

Although Kepler prepared himself for a career as a Lutheran pastor, he accepted the first job offer he received—that of a secondary school teacher and district mathematician in a provincial outpost. One day in 1595 while at the blackboard, sketching the repetition pattern of Jupiter-Saturn conjunctions for his class, he experienced an epiphany. Geometry and divinity combined in his mind, helping him intuit the solution to three cosmic mysteries: why the planets assumed their specific distances from one another, why God had created only six of them, and why they revolved at different speeds around the Sun. In the first moments of excitement, Kepler envisioned the spheres of the planets as though each were inscribed inside a particular form of regular polygon—from triangle to square, pentagon, hexagon, and so on. But, since there were any number of regular polygons and only six planets, Kepler soon scrapped them for their rarer three-dimensional counterparts, called regular solids. The simplest of these, the tetrahedron, with four faces made by four identical equilateral triangles, fitted handily between the spheres of Mars and Jupiter. The cube (comprising six equal squares) accounted for the distance between Jupiter and Saturn, and the dodecahedron (consisting of twelve cloned pentagons) accommodated the Earth within the orbit of Mars. The glorious confluence of the five regular solids with the five interplanetary interstices flooded Kepler’s soul. It brought him to tears and redirected all his efforts.

“Days and nights I passed in calculating,”
he reported in his 1596 book,
Mysterium cosmographicum
, “to see whether this idea would agree with the Copernican orbits, or if my happiness would be carried away by the wind.” At length he made everything fit. But he craved further confirmation, and that, Kepler knew, could come only from Tycho—from the trove of observational data collected over decades with scrupulous attention to detail.

Tycho had need of Kepler, too—of the German mathematician’s superlative ability to mine the data for its hidden wealth. If, as Tycho believed, his data verified his version of cosmic order, then his life work would surpass that of Ptolemy and reward his every sacrifice. But Tycho worried that Kepler, a confessed Copernican who had reprinted Rheticus’s
First Account
as an appendix to his own
Mysterium
, might uncover incontrovertible evidence for the rival theory—or that he might twist evidence that favored the Tychonic system to feign support for the Copernican. Thus the distrustful Tycho dallied, making Kepler pant for every bit of data he deigned to release. Only after Tycho’s sudden death, in October 1601, and the inevitable struggle with Tycho’s heirs over access to the data, did Kepler finally take possession of Tycho’s treasure and lay it at Copernicus’s feet.

Johannes Kepler, imperial mathematician to Rudolf II.

“I build my whole astronomy upon Copernicus’s hypotheses concerning the world,”
Kepler proclaimed in his
Epitome of Copernican Astronomy
. He thanked Tycho for his observations, but dismissed the Tychonic system as inferior. The Earth, he averred, most assuredly moved among the planets, around the Sun, just as Copernicus maintained. But Copernicus had centered the planets’ revolutions on a point near the Sun, rather than on the Sun itself. Kepler found this notion physically implausible, so he corrected it. He relocated the center of all planetary motions in the body of the Sun, and imbued the Sun with a force that spread like light through the universe, pushing the planets now faster, now slower, depending on their distance. Not only did the planets nearest the Sun outpace the farther ones, as Copernicus had remarked, but each planet periodically altered its own distance from the Sun, and changed its speed accordingly. Kepler proved the path of a planet was not a perfect circle, or any combination of perfect circles, but the slightly flattened and double-centered circle known as an ellipse, with the Sun at one focus.

Kepler’s ever-so-slightly squashed Martian orbit barely deviated from perfect roundness, even though it proved more elliptical than that of any other planet. For this reason, Kepler considered Mars’s path—the one most closely trailed, most richly documented by Tycho—the “only possible” route to the truths of a “New Astronomy,” rooted in the laws of physics. Had he tackled Jupiter or Saturn, for example, the subtleties of the ellipse would have escaped his notice and caused insuperable problems.