Tycho and Kepler

by Kitty Ferguson

  Young Johannes, the eldest of the children, resembled Katharina in appearance. They were also alike in having restive, inquiring minds, but Katharina had no education, and her interests were herbs and homemade mixtures for healing. What in her son would develop into a rich intellectual curiosity was, in her, often only nosiness. When Heinrich was at home, she responded with pouting and stubbornness to his harsh, rude treatment. “She could not,” wrote Kepler with pity, “overcome the inhumanity of her husband.”

  Kepler also described aunts and uncles and some cousins who lived in the house in Weil der Stadt. Among them were Uncle Sedaldus, who was “an astrologer, a Jesuit, acquired a wife, caught the French sickness, was vicious,” and Aunt Kunigund, who was poisoned and died.

  In the spring of 1575 Katharina Kepler left three-year-old Johannes and his infant brother in the care of these relatives and went off to follow her soldier husband Heinrich. In her absence Johannes nearly died of smallpox, probably the illness that impaired his vision. The prodigal parents returned after a year.

  With both nature and nurture decidedly against the two Kepler brothers, their future looked bleak. Johannes was puny and weak-sighted. Heinrich, two years younger, was an epileptic. Johannes recalled that Heinrich was beaten roughly, and animals frequently bit him. He nearly drowned, nearly froze to death, nearly died of illness, and ran away from his apprenticeship to a baker when his father threatened to “sell him.” After that he appeared only occasionally at home, much as his father did, often returning bruised and broken, robbed of everything he had, making his way back by begging. All his life—he died at the age of forty-two—his mother considered him the bane of her existence.

  The younger Kepler children turned out better. Margarethe, a gentle, sympathetic girl, later married a clergyman, and she remained close to Johannes and loyal to her mother even through the worst of times. The youngest surviving sibling, Christoph, grew up to be an honorable, correct man, though not so unfailingly loyal as his sister. He became a respected craftsman, a pewterer.

  The little city of Weil der Stadt, surrounded on all sides by the duchy of Württemberg, nevertheless enjoyed the status of an imperial free city within the Holy Roman Empire and sent its own representative to the Imperial Diet. Though its name implied that the Holy Roman Empire was in some way the legatee of the Roman Empire, the standard and fairly accurate quip is that it was not holy, not Roman, and not an empire. Ruled in theory by the Holy Roman Emperor in Prague and the Imperial Diet, it was made up of many units—duchies like Württemberg, cities like Weil der Stadt, bishoprics, and other principalities—that today have become Germany, Austria, and the Czech Republic, as well as parts of Poland, France, and Holland and sundry other bits and pieces of Europe.

  Under the 1555 Peace of Augsburg each local leader decided whether Catholicism or Lutheranism would be practiced in his domain. An exception was made for free imperial cities like Weil der Stadt: If both religions had previously been practiced there, both were allowed to continue. The duchy of Württemberg, which surrounded Weil, was by decree of its powerful duke officially and vehemently Lutheran. Weil itself was mostly Catholic, but there were Lutherans there as well. The Keplers were part of this Lutheran minority—a not entirely comfortable situation, though grandfather Sebald seemed not to have found it an impediment to political advancement.

  In 1576 Johannes’s father renounced the right of citizenship in Weil and moved his young family to Leonberg, not far away but part of Lutheran Württemberg. It was from the hill above that town that Katharina and Johannes viewed the comet.

  TYCHO BRAHE and other scholars, though not immune to the disquiet about the comet felt by less educated people like the Keplers, undertook to study it zealously from a scientific point of view. Tycho’s first step was to write a careful description5 and make a drawing. The comet’s head was seven to eight arcminutes in diameter and bluish white, the color of Saturn. Its tail was reddish, like a flame seen through smoke. To pinpoint its position, he measured its angular distance from two prominent stars. Tycho wanted to find out how far away from Earth the comet was, and that meant, as it had for the nova, finding out whether it displayed any parallax shift.

  Looking for the comet’s parallax presented new challenges. It was positioned too near the Sun to be visible except for an hour or so just after sunset, and that was too short an interval for Tycho’s position on Earth to change sufficiently to provide any perspective on it. Furthermore, it was known that comets were in motion. With the nova, Tycho had been able to assume that any movement it displayed against the background was a manifestation of parallax. He could assume no such thing for a comet. Its change of position against the background would be partly, maybe totally, attributable to its own motion. Without knowledge of what that motion was, any attempt to measure parallax would be futile.

  Partly due to cloudy weather and the wait for longer evening visibility as the autumn days grew shorter, it took Tycho ten days after he first saw the comet to determine that it moved an average of about three degrees of arc per twenty-four hours. Because every twenty-four hours brought Tycho back to the same viewing position, that motion could not be attributable to parallax: It had to be the comet’s own motion. Three degrees of arc per twenty-four hours is about seven and a half minutes of arc per hour. Tycho next made observations three hours and five minutes apart, during which interval the comet’s own motion—the seven and a half minutes of arc per hour—should have moved it, he calculated, about twenty-three minutes of arc. If it appeared to move more or less than that, the difference would be attributable to a parallax shift. Tycho found that the comet appeared to move only twelve minutes of arc. Parallax shift, he concluded, had to account for the other eleven minutes of arc

  That result was disappointing. It was a borderline case whether this amount of parallax indicated that the comet was above or below the Moon. Further study soon yielded something more decisive. Tycho reconsidered the comet’s daily intrinsic motion and found it closer to two degrees than three. He did the calculations again, and this time he discovered almost no motion left over to be accounted for by parallax. Additional observations near the end of December bolstered the case for the comet having virtually no parallax at all. Tycho saw the fading comet for the last time on the twenty-sixth of January, when the Moon, which had drowned out the comet’s light for two weeks, had waned enough to allow him one last glimpse. He had already begun to write his conclusions.

  Tycho felt he had settled the question of whether comets are closer than the Moon or farther away. Aristotle had been wrong about the “unchanging” heavens. This comet was a change, and it was indisputably beyond the Moon, though Tycho could not specify precisely how far beyond.

  Tycho reached a second conclusion. The comet moved in the same direction the planets move, and this movement had for the first week carried it out very rapidly in front of the Sun, but after that it had moved more slowly and become dimmer, suggesting it was moving farther away from Earth. Then the Sun had begun to catch up again. Tycho concluded that the comet was orbiting the Sun.

  He began to plan a book. He knew from previous experience that it was difficult to change the views of his colleagues and the public that followed them blindly. His new book needed to be more rigorous, more detailed, longer, than its competitors. While the comet was still visible, Tycho started a notebook of star observations so that he could use his own coordinates for reference stars to locate the comet rather than rely on the old catalogs.

  The first order of business, however, was to file a private report to the king. It was only a little embarrassing that Frederick had seen the comet two days earlier than Tycho. Someone at Sorø Abbey, where the court was lodged at the time, had pointed it out. Tycho had also been preempted in his royal reporting by one Jørgen Dybvad, an open-minded man when it came to Copernican astronomy but preoccupied in the present case with what the comet portended. His pamphlet predicted bad weather, crop failure, religious troubles, pestilence, war, ev
en that “the day of the Lord . . . is at hand.” Dybvad was an ambitious and powerful figure at court and in the university and a potential competitor. Tycho saw an opportunity to best him.

  His report to Frederick began with a description of the comet, including technical details that he promised to expand on in a later, more formal publication. This material could not have been of enormous interest to Frederick, but Tycho saw it as a way of reinforcing his image as an expert and giving greater credence to his interpretations as an astrologer. The next part of the report obviously referred to poor Dybvad: “Pseudoprophets6 who have thought [that comets might presage the apocalypse] and have mounted too high in their arrogance and not walked in divine wisdom will be punished.” Tycho was not, however, ready to say there was nothing to worry about. Historically, he reminded the king, comets had always meant “great scarcity . . . many fiery illnesses and pestilence and also poisonings of the air by which many people lose their lives quickly . . . great disunity among reigning potentates, violent warfare and bloodshed and sometimes the demise of certain mighty chieftains and secular rulers.” Because of its position in the sky and other characteristics, this comet was worse than usual and augured “an exceptionally great mortality among mankind.”

  With his reader now brought to the point of despair, Tycho advanced the more soothing and optimistic theme of the arguments he had made in his first university lecture—that heavenly events do not determine the future. Resorting to anguished prayer was not the proper course, he advised, for rational exercise of free will and appropriate action could change the effects of the comet. The king might even prepare in advance to reap the benefits if the prediction about the “demise of certain mighty chieftains and secular rulers” should turn out to apply to Ivan the Terrible of Russia. And Frederick would be wise to get ready for “Spanish treachery” if the comet had special “significance over the Spanish lands and their reigning lords.” Tycho continued in this vein, knowing that these interpretations in terms of political policy would appeal to Frederick. When it came to demonstrating the value of astronomy and astrology to the king—and implying that it was an extraordinary advantage to have Tycho himself at the king’s right hand rather than a defeatist like Dybvad—Tycho was playing it to the hilt.

  The report also revealed a trend in Tycho’s thinking—or perhaps it was merely rhetoric—that the king may not completely have shared. Tycho painted himself as a man who not only abhorred the politics of court life but also longed for peace and justice on a wider than personal scale. The comet, he wrote, might mean “well-deserved punishment for inhumane tyranny,” and for “those who were associated with [violence and warfare], those who are always on the prowl [causing] great injury to others.”

  If the peasants on Hven had been able to read their master’s hyperbole about “well-deserved punishment for inhumane tyranny,” they might well have responded with rude noises, for during the same visit Tycho asked Frederick for assistance in dealing with the peasants who were fleeing Hven. These deserters, Tycho pointed out correctly but also self-righteously, were violating the law of villeinage and thus placing a greater burden on those who remained. The king’s reply made it clear that the law that applied elsewhere also applied on Hven: Tenants could leave an estate only with the permission of their lord.

  It was possibly also on this occasion that Frederick reiterated his promise to Tycho of the canonry at Roskilde Cathedral on the death of an incumbent. He could look forward to the incomes from endowments of the Chapel of the Magi there.

  Tycho’s ties to the king grew even stronger in the summer of 1578 as the construction progressed at both Uraniborg and Kronborg, the new palace at Elsinore. Craftsmen, materials, and architectural ideas moved swiftly back and forth across the sound.

  For his “architect” Tycho had made an unlikely but inspired choice. Hans van Steenwinkel was a Dutch master mason who came to work for King Frederick at Kronborg. Tycho brought him across to Hven, hoping he might be trainable as a master builder. He gave Steenwinkel some instruction in astronomy and geometry, explained the symmetrical scheme of the building and grounds, and set him to work drawing more detailed plans. Steenwinkel was a quick study. Before long he had mastered classical and Italian Renaissance architectural theory as well as perspective drawing and was producing designs for windows, spires, domes, and other architectural details that pleased even the exacting Tycho. So great was Tycho’s confidence in Steenwinkel that he put him fully in charge of the construction.

  A few months after Steenwinkel came, Tycho engaged a twenty-three-year-old university graduate named Peter Jacobsen Flemløse to assist him in astronomy, alchemy, and other work—the first of a long procession of assistants and students that would finally end with Johannes Kepler. Flemløse, like Steenwinkel, was able and quick-witted. Tycho taught him to use the cross staff and the sextant and delegated to him the task of compiling a new catalog of reference stars for the comet. Flemløse also liked to draw, and from this time forward whimsical pictures adorned Tycho’s star catalogs and observational journals.

  When the building season slowed down once again in the autumn of 1578, Tycho’s interest turned back to the comet and his book. He gathered all the observations7 he had made of distances from the comet to twelve stars, as well as descriptions of the observing conditions (the weather and other things such as moonlight that affected the observations), and put this material in the first chapter—an unusual way to begin in Tycho’s day. It was unprecedented for anyone to share so much data with his readers. The book was also unusual in its author’s willingness to admit error and his capacity to analyze why the error had occurred. On the first night of observation, the position of the comet figured from the twelve stars was at odds with the position figured from the Moon. Tycho left this discrepancy in the book, permitting his readers to see the conflict. Later, when printing was almost completed, he found the reason for the problem and added an “annotation by the author derived from later observations of the Moon.”

  With so much introductory material, it took Tycho ninety pages to get to the real crux of the matter: whether the comet was higher than the Moon. By now he was more convinced than ever that it was, and that the comet moved in a great circle, like the Sun, the Moon, and the planets, though with a less regular motion. He estimated that the comet came no nearer to Earth than six times the minimum distance of the Moon.

  In December another royal prince was born, and that meant another horoscope, but Tycho was not averse to setting his book aside. There was already a plethora of commentaries on the comet coming off the printing presses of Europe. Tycho knew that he would have to produce something extraordinary to make an impact, and, curious about what his competitors were saying, he began collecting, through friends abroad, all the publications on the comet that they could put their hands on.

  AFTER HEINRICH KEPLER moved his family, including four-year-old Johannes, away from the overcrowded house in Weil der Stadt to Leonberg in 1576, he stayed with them only about a year before leaving again to sell his services to the Belgian military. Home became a more peaceful place for Katharina and her children. But Heinrich’s Belgian adventure was a disaster. He lost what little fortune he had and nearly ended on the gallows. He trudged back to Leonberg and announced that they had to sell the house. The family moved to a rented property in Ellmendingen. After three years of near destitution, they somehow managed to acquire some property back in Leonberg and return there. It was at about this time that Johannes, reading of Jacob and Rebecca in the Bible, decided that if he should ever marry he would take them as a model. Their faithfulness was a marked contrast to his unstable and undependable parents. Five years after the move back to Leonberg, when Johannes was sixteen, Heinrich abandoned his family forever. Johannes never saw his father again.

  Johannes would grow up an ardently religious man whose life was repeatedly, tragically disrupted by the political/religious strife around him. Nevertheless, at the start, the religious establishment se
rved him well. The Lutheran Church’s commitment to education provided a singular stroke of good fortune in an otherwise hopelessly bleak childhood. The Lutheran duchy of Württemberg had established a fine free school system, and this system rescued Johannes.

  Much more information survives about Kepler’s school days than about Tycho Brahe’s. Johannes began at the German Schreibschule in Leonberg, where pupils learned to read and write the German they needed for everyday life. His teachers recognized an exceptional young mind and transferred him to a “Latin school.” The dukes of Württemberg had established such schools in all small towns like Leonberg.

  Johannes’s transfer was a significant advancement, for Latin schools were the Lutheran substitute for the monastery schools that, before the Reformation, had provided primary education for boys who would become civil administrators, clergymen, and scholars. Latin was the common language in which educated men all over Europe communicated, lectured, debated, and wrote books; and Leonberg’s Latin school set its boys firmly on this path by requiring them from the start to converse with one another day and night in Latin, or not at all. In the first year, they learned to read and write the language; in the second they endured endless grammar drills; in the third they read the classical texts.

  It took Johannes five years to complete the three-year course. The move to Ellmendingen interrupted his education when he was about eight and had been a pupil in Latin school for a year. During that period of abject poverty, his parents set him to heavy agricultural labor rather than allow him to continue in school. Those two years were hellish for Johannes, for not only was he an undersized weakling of a child, pathetically unsuited for such work, but he loved school. His one source of happiness had been snatched away. However, when the family fortunes improved, his parents reenrolled him at age ten. Two years later, in 1584, he passed the competitive examination marking the end of Latin school and moved on to the “lower seminary” at Adelberg, where his room, board, and tuition again were free, courtesy of the duchy. After two years there he advanced to the “higher seminary” at the former Cistercian monastery at Maulbronn for two more years of study. Maulbronn was a preparatory school for the University of Tübingen.