The Theory of Heliocentrism

The comet of 1577 wound up having a profound impact on the course of history, in a far more direct way than the soothsayers and mystics believed it would. For, in addition to Tycho Brahe, it was seen by a five-year-old boy who lived half a continent away from the prodigious Dane, in the southern German town of Weil der Stadt. The boy in question was none other than Tycho’s later correspondent Johannes Kepler. When the comet first appeared, the young Johannes and his mother climbed a hill just outside of town to gaze upon the celestial newcomer for the entirety of an evening. He would go on to remember that evening not just as one of the few pleasant interludes of an extremely difficult childhood, but as the precise instant when his fascination with astronomy began.

Little Johannes was the first of eight children in his family, of whom just four would survive into adulthood. He himself very nearly succumbed to smallpox at the age of three. He went on to bear the physical scars of this brush with death as surely as he did the psychic traces of his brush with the comet. His motor skills were affected, so that he moved in a jerky, scuttling way; his hands curled upon themselves and lost their dexterity, becoming more like claws. Throughout his life, even the most innocuous nicks and scrapes would take an inordinate amount of time to heal, oozing blood and putrid puss in the meantime. Worst of all for a would-be astronomer, his eyes were left watery and weak. In a different era, those around him might have said that he looked rather like a character from a B-grade horror movie — a little Igor seeking his Dr. Frankenstein. In this one, they tended to just dismiss and scorn him.

No one was more scornful than Johannes’s own father, a mercenary who made his living fighting in wars as far away as Flanders and the Netherlands. When he wasn’t out campaigning, he fought in the taverns of Weil der Stadt instead, then came home to knock his wife and children about. The ugly, sickly runt Johannes was not at all the first-born son he had had in mind. Johannes would later remember his father as “a vicious man, with an inflexible nature, a quarrelsome man who was doomed to a bad end.” His mother was only a little better, being merely slatternly and neglectful rather than actively cruel.

Just to compound Johannes’s sense of alienation from his surroundings, his parents were Protestants, dwelling in a largely Catholic town. They were tolerated there, thanks to the delicate truce that was maintained between the two branches of the Christian faith in some parts of Germany at the behest of the Holy Roman Emperors, who lived in constant fear of the full-on civil war over religion that could easily splinter their realm forever. But the Kepler family were outsiders all the same, prevented from playing any sort of role in the civic life of Weil der Stadt. Small wonder that this malformed child who was shown so little love or kindness became a misanthrope, reflexively inclined to think the worst of everyone.

Yet for all his manifest physical deficiencies, there could be no denying that Johannes was smart. The same year that he saw the comet, a teacher at his local school who shall forever remain anonymous quite probably changed the course of history when he went to the boy’s parents and told them that the few years of part-time education his institution could provide, aimed at turning out minimally literate farmers and burghers, was inadequate for a lad of Johannes’s intellect. He should be sent to a grammar school to learn Latin and join the truly educated circles of Europe. One can all too easily imagine his benighted parents’ scoffing reaction to this news that they had a budding scholar in their family. But the teacher was ready with an answer to this as well: he might become a professor or a Lutheran pastor, or both, jobs which came complete with considerable prestige and reasonably good salaries. After all, his physical condition made it clear enough already that he had no future whatsoever as a soldier, a craftsman, or even just an ordinary laborer. Thanks to this rare intervention by someone who by all indications genuinely wanted the best for him, Johannes got his chance in life.

He excelled at his studies. At the age of eleven, he was selected by his teachers to travel twenty miles (32 kilometers) to Protestant Stuttgart, the capital of the Duchy of Württemberg to which Weil der Stadt belonged, to sit for an exam. If he passed, he would become one of the handful of students who were taken under the wing of the duke of Württemberg each year, given a full scholarship to a Lutheran seminary school in return for a pledge to serve the duke in whatever capacity they might be needed. Johannes did pass the exam, with flying colors.

Almost in spite of himself, he was moving rapidly up in the world, into a social stratum well out of the reach of the rest of his family. In 1588, when he was sixteen years old, Johannes enrolled at the University of Tübingen. The following year, his father went off to war yet again, this time to fight for the king of Naples (the same monarch in whose employ the father of Giordano Bruno had marched). This time he never returned. Johannes didn’t much care. By now as fluent in Latin as he was in his native German, he had moved on to studying Greek and Hebrew, as well as theology — a lot of theology — plus natural philosophy, mathematics, and astrology, the last of which Kepler believed in as unquestioningly as any of his peers. His old life back in Weil der Stadt seemed a long, long way away.

When it came to the more practical discipline of astronomy, that prerequisite for casting adequate horoscopes, Kepler was fortunate enough to have an instructor by the name of Michael Mästlin, himself an astronomer of some note. Kepler “listened attentively” to him. Mästlin introduced the teenager to the heliocentrism of Copernicus almost as he might an occult secret known only to initiates, after Kepler had begun to complain to his instructor about “how awkward in so many ways the customary notion of the structure of the universe had become. I was delighted, therefore, by Copernicus. I bit by bit gathered together all the mathematical advantages that Copernicus has over Ptolemy.”

As we have seen, unadulterated heliocentrism was a mental leap that Tycho Brahe, the most famous of all European astronomers at this time, had never been able or willing to make. At their university, Mästlin and Kepler were the only people who embraced heliocentrism. Knowing how controversial the theory was with theologians and natural philosophers alike, Mästlin was circumspect about his adherence to it; Kepler was not. He argued the case for heliocentrism loudly and stridently, endearing himself to no one. Much the same could be said about countless other subjects having nothing to do with astronomy.

The Johannes Kepler of Tübingen was perhaps no longer the shirking, sarcastic, supremely uncuddly child he had been in Weil der Stadt, but he wasn’t anyone’s ideal of an urbane party guest either. He was self-aware enough to recognize his own social inadequacies — a tendency to be blunt where a measure of indirectness would serve him better, a tendency to laugh where he shouldn’t and not laugh where he should, a tendency to point out minor mistakes that he could more profitably have let pass by — even as he couldn’t see his way to correcting them. If he had lived in our time, he might have been diagnosed on the autism spectrum. As it was, his own third-person evaluation of his social presentation was lacerating.

The man has in every way a dog-like nature. Even the food is the same for both: he likes gnawing on bones and chewing on dry crusts. He is content with even the cheapest food. He shudders at baths, medicinal dips, and lotions, just like a dog.

He is impatient in conversation, and those who come to the house frequently he greets as a dog would. The instant someone snatches even the smallest thing away from him, he growls, flares up, like a dog. He is tenacious. He persecutes everybody who acts badly — that is, he barks at them. He bites, and is quick with sharp derision. Therefore he is hateful to most people and is avoided by them…

Sad as it is to say, there was evidently a good deal of truth to this merciless self-evaluation. Suffice to say that Johannes Kepler was not the most popular student at his university, among his peers or his professors. No one was quite sure what to do with him; between his acerbic mode of argumentation and his thoroughgoing social awkwardness, he seemed well-suited to become neither a pastor, a diplomat, nor a civil servant, the most common career choices for a university graduate without a claim to nobility or inherited wealth.

So, when the university received a letter from a Lutheran seminary school in the Austrian town of Graz at the beginning of 1594, asking for a teacher of mathematics to replace one who had just died, the professors and administrators leaped at the chance to get this troublesome iconoclast and his uncomfortable questions and positions out of their hair. They in turn wrote to the duke of Württemberg to ask him to send this young subject who had pledged himself to his service to Graz. When the royal order duly came, Kepler had no choice but to obey, even though he was still one year short of attaining his degree from the university. In March of 1594, when he was 22 years old, he set off on the journey, first by horse to Ulm, then by barge down the Danube to Linz, and then overland once more to his new home.

Graz was a mid-sized town with a history and a contemporary importance well out of proportion to its size. It had been the seat of the Holy Roman Emperor himself for a time during the last century, and it remained the home of the archdukes who ruled Austria more directly as imperial electors. Both emperors and archdukes belonged to the house of Habsburg, the most long-lived and far-reaching locus of ancestral power in all of European history. Traditionalists by nature, the Habsburgs publicly proclaimed themselves to be staunch Catholics. That fact notwithstanding, Graz was one of those mixed-up Germanic towns that the rest of Europe found so strange, a place where Protestants and Catholics lived side by side with a degree of equanimity.

For all that Kepler was no one’s idea of a socially astute young man, he could hardly have been socially oblivious enough not to recognize that he had been shunted off down south because the University of Tübingen wanted to be rid of him. Still, he found that life in Graz wasn’t as bad as it might have been. His reputation as a stern and demanding teacher preceded him, such that there were usually only a few students enrolled in his courses. He made a decent salary despite this fact, and supplemented his income by casting horoscopes. The rest of his time he used on writing a book, a grand metaphysical theory of the heavens drenched in the Christian religion and other, more ancient sorts of mysticism. He positively burned to be accepted by — and then to debate with — the foremost minds of Europe. While he was trying to make inroads with Nicolaus Reimers and Tycho Brahe, the alpha and omega of European astronomy, he also continued to correspond with Michael Mästlin. One subject which the two men discussed — in fact, one on which they strongly disagreed — is worth delving into in some detail here, both for its own sake and for what it has to tell us about the tenor of Kepler’s era and Johannes Kepler himself.

There are two obvious ways to mark the passage of time by making reference to the heavens. The Sun, of course, rises and sets in cycles that we have chosen to call days. And the Moon waxes and wanes in cycles that themselves last about 28 of these days, the original length of a month. (There is a reason that “Moon” and “month” are such similar words, not only in English but in most Western languages.) Yet there is one other incredibly important earthly cycle that cannot be so easily tracked in the sky: the cycle of a year. Frustratingly, a year corresponds to neither an integral number of solar days nor an integral number of lunar months. In light of this, any system of timekeeping on an annual scale was doomed to be messy.

The ancient Egyptians looked beyond the heavens to come up with the best system of anyone during the dawning millennia of human civilization, by taking advantage of the most unique single attribute of the land in which they lived. From the building of the first sedentary communities in Egypt in 5000 BC or earlier until the construction of the Aswan Dam in the 1960s of our era, the rhythm of life in Egypt was that of the benevolent Nile River, which every year began to increase its flow of water in early June by our modern reckoning, until it burst its banks entirely in early August. The flooding reached its maximum extent a month later and then ebbed away again a month after that, leaving behind fecund soil that was primed for agriculture, thus making a sophisticated civilization possible in this otherwise harsh and inhospitable desert land; not for nothing did the ancient father of history Herodotus call Egypt “The Gift of the Nile.” In fact, the annual flooding of the Nile was so astonishingly regular that it provided the Egyptians with another gift beyond the obvious one of food to eat: by carefully measuring the depth of its water using devices that came to be known as “nilometers,” they could use the river as a non-celestial point on which to anchor a calendar. Through this method, the Egyptians determined that there were 365 days — or thirteen cycles of the Moon, plus one extra day — in a single year. But eventually the Egyptians chose  to decouple their calendar entirely from the Moon, because thirteen months were impossible to divide neatly into seasons. Thus they adopted a calendar consisting of twelve months of 30 rather than 28 days each, with five days tacked onto the end of each year, a time for feasting and celebration of auld lang syne.

The Egyptians later found another, even more reliable linchpin to which to anchor a year, one that did make use of the heavens. In mid-summer by our reckoning — the exact date has slowly changed over the millennia — Sirius, the brightest star of all, stands over Egypt in a direct line with the rising Sun only one time per year. Over the course of decades or centuries of careful observation, the Egyptians deduced from this celestial cycle that the real length of a year was more like 365 and one-quarter days. Thus was born a quadrennial leap year, in which the period of partying was extended one day more. (Presumably no one complained.)

Even in 46 BC, long after the heyday of ancient Egypt, its calendar remained the best ever invented. That year Julius Caesar of Rome, needing an official, standardized calendar by which to administrate a burgeoning empire, asked some of his cleverest bureaucrats to come up with such a thing. The so-called Julian calendar that was introduced a year later borrowed heavily from the Egyptian one, but moved its starting point half a year away and dispensed with the extra days that didn’t belong to any month in favor of the twelve asymmetrical months, with lengths ranging from 28 to 31 days, that we still know today. Every fourth year continued to be a leap year, when the shortest month of February was given an extra day.

The Julian calendar did indeed become the standard of the Roman Empire, then remained the standard for all of Europe and adjacent lands after said empire fell. It was still the standard in Nicolaus Copernicus’s day, still the standard when Giordano Bruno and Tycho Brahe and Johannes Kepler were born. It stands today as the most successful single bureaucratic initiative in all of Western history, by far the most enduring single achievement of all of the legendary figure who lent it his name. By giving Europe a way to talk to itself about time, it made commerce, culture, and the very concept of a shared past, present, and future possible.

But for all its utility, the Julian calendar wasn’t perfect. It assumed that the exact length of a year was 365 days and six hours. In actuality, however, it takes the Earth 365 days, five hours, 48 minutes, and 46 seconds to complete one orbit around the Sun. This discrepancy of a little over eleven minutes was trivial on the scale of individual years and even decades, but began to add up as decades became centuries. By the late 1500s, ten “extra” days had been added to the calendar, with the result that it had fallen out of sync with the lived reality of the annual seasons: what used to be the first week and a half of one season had become the last week and a half of the one before. The equinoxes and solstices were now occurring on the eleventh instead of the 21st day of their respective months. The rhythms of agriculture, as important to contemporary Europe as they had been to ancient Egypt, were no longer in tune with the calendar. Clearly something needed to be done to make the calendar correspond once again with nature. But a fragmented Europe had no Julius Caesar who was capable of pushing through a change of such magnitude.

Or did it? In 1582 — when Giordano Bruno was living the life of an itinerant intellectual rebel, Tycho Brahe was holding court on Ven, and Johannes Kepler was preparing to sit for an all-important exam in Stuttgart — Pope Gregory XIII followed the advice of some of his more enlightened functionaries and introduced a new calendar. There would be no October 5 through October 14 in this year of 1582, he declared. Instead all good Catholics would go to sleep on the evening of October 4, only to wake up on the morning of October 15. To prevent the calendar from falling out of sync again in the future, the first year of each century would no longer be given an extra day, unless it happened to be divisible by 400. This Gregorian calendar, the one by which we still live today, isn’t perfectly in sync with the length of a solar year, but it is close enough that it shouldn’t need even slight tinkering for at least another 3000 years.

In addition to being a landmark event in the history of science and timekeeping, Gregory’s bold decree marks a more melancholy milestone in the history of the Catholic Church. Gregory XIII was by no stretch of the imagination a progressive in most respects; this was the same pope who led the people of Rome in song to celebrate the massacre of tens of thousands of French Protestants, who urged Catholic monarchs to launch military assaults against their Protestant peers, who actively plotted murder against Queen Elizabeth I of Protestant England, who gave his full-throated support to the tortures and executions perpetrated by the Inquisition all over Europe. Nevertheless, the Gregorian calendar which he initiated has gone down in history as the last gasp of the old free- and forward-thinking wing of the Catholic Church that had once been so ably personified by the towering figure of Erasmus. Not only was it the last time that an increasingly hidebound Church would dare to make such a dramatic break with the past, but it came near the end of the epoch when the pope had enough intrinsic authority for the whole question not to be moot anyway.

As it was, the erasure of ten days from the lives of the people by papal fiat brought with it no small degree of angst. The lower classes in some places rioted to demand that they be paid a full month’s wages for that October, and the French philosopher Michel de Montaigne wrote how “the eclipsing or bridging of ten days, which the pope hath lately caused, hath taken me so low that I can hardly recover myself.” Yet in the end, Catholic Europe sucked it up and went along with Gregory’s disorienting decree.

But whereas the Gregorian calendar was accepted in Catholic Europe, albeit in some cases grudgingly, it was rejected as a matter of course in the Protestant lands. Kepler’s mentor Michael Mästlin was one of the most vocal among the naysayers, publishing no fewer than four separate diatribes condemning the new calendar itself and the sheer arrogance of the pope who dared to try to impose it. Why, he asked, should this antichrist who falsely claimed to speak for God be accorded the right to erase ten days from the lives of those people who had been wise enough to reject his hypocrisy? Mästlin’s tone was perchance so strident because he was learned enough to know deep down that the Gregorian calendar really was better, that it was a smart, relatively painless, enduring solution to what really had become a serious problem. Few things are harder for most of us to do than to acknowledge it when our enemies have right and logic on their side.

Mästlin certainly wasn’t alone in cutting off his nose to spite his face in this matter. All of Protestant Europe initially dismissed the Gregorian calendar with similar knee-jerk indignation. Protestant Germany, Scandinavia, and the Netherlands wouldn’t accept it until 1700, England not until 1752. Off to the east, it took the out-with-the-old, in-with-the-new Bolshevik Revolution of 1918 to finally break the ability of the Russian Orthodox Church to resist it. In the meantime, to the other infelicities of the Julian calendar could now be added the headache of constantly needing to convert the date in one part of Europe to the date in the other part, the very problem Julius Caesar had originally set out to solve. (Needless to say, this annoyance is doomed to dog historians of the era of dueling calendars forever.)

And yet there was an exception to the Protestant world’s vehement rejection of Pope Gregory’s calendar, in the person of none other than Johannes Kepler. “It is 150 years since astronomers demanded legislation for some correction,” he wrote in a letter to Mästlin. “Now one correction has been made. No one can easily introduce another into a small part of Europe without great disturbance. Therefore either the old form must be retained or the Gregorian accepted. It is a disgrace to Germany that they who discovered the art of reformation should remain unreformed.” This argument that cast the change of calendars in the same moral light as the Protestant Reformation itself did not go down well with his old professor. At the same time, Mästlin must surely have known that he had no logical argument to make for retaining the Julian calendar, only emotional ones of the sort that Kepler would demolish contemptuously.

This argument  may seem trivial in light of what Kepler would go on to achieve, but it illustrates, I think, something extremely important about the man’s character. Unlike the other minds we have met thus far, he had the rare quality of being absolutely uncompromising in his pursuit of truth. Emotion, tradition, intimidation, even friendship… none held any weight in comparison. Even the great empiricist Tycho Brahe was prepared to twist himself into knots in order to retain some vestige of the Earth-centered universe with which he had grown up. Not so Johannes Kepler.

That said, Kepler definitely wasn’t immune to scurrying down blind alleys overenthusiastically in the midst of his pursuit of truth. In December of 1596, with the help of Michael Mästlin, he got his Mysterium Cosmographicum published — or, to use its full translated title, Collection of Cosmological Dissertations, Containing the Cosmological Mysteries, the Forerunner of the Cosmological Essays Which Contain the Secrets of the Universe on the Marvelous Proportions of the Celestial Spheres and on the True and Particular Causes of the Number, Size, and Periodic Motions of the Heavens, Established by Means of the Five Regular Geometric Solids. The rest of the muddled book was exactly as readable as its title, the epitome of a neophyte scholar trying way, way too hard.

Nonetheless, as we saw in our last chapter, the book raised Kepler’s stature enough to make him a regular correspondent with Tycho Brahe. He was soon trying his awkward best to backpedal on his earlier overtures to Nicolaus Reimers, as we likewise saw. For his part, Tycho seems to have recognized Kepler’s book for the nonsense it mostly was, but he was intrigued enough by the young man’s turn of mind to keep answering his letters.

In the meanwhile, life went on in Graz. In April of 1597, following a long and sometimes fraught courtship, Kepler got married to one Barbara Müller, the daughter of a local Protestant miller. She was a pretty woman of 25 years, just one year younger than Kepler, but she had already lost one husband through death — she had had a daughter named Regina with this man, who also joined Kepler’s household — and another through a scandalous divorce. This made her damaged goods by the standards of the time, and is probably the only reason she and her fairly prosperous family were willing to accept this hunched, crooked-looking scholar of modest income and scant social grace. Inveterate watcher of the heavens that he was, Kepler couldn’t help but notice that the day of their wedding was marked by “pernicious” skies. And indeed, their marriage would prove loveless; Kepler would come to describe his wife as “stupid” and “sulking.” She would spend much of her time in bed, in the grip of an endless series of illnesses real, feigned, or imagined; who can possibly say from this remove in time?

But the disappointments of Kepler’s home life would shortly be eclipsed by other problems. He was about to learn how fragile religious freedom could be under a monarchical government where tolerance and intolerance were balanced on the whims of a single man.

Four months before Kepler’s wedding, an eighteen-year-old Habsburg prince named Ferdinand had become the latest archduke of Austria. Unlike his uncle, the less than personally pious Holy Roman Emperor Rudolf II, Ferdinand was a full-blown Catholic zealot who ardently desired to return the Protestants in his realm to the One True Church, by force if necessary. He took the Lutheran steeples which he could see from the windows of his castle in Graz as a personal affront. A series of ever-stricter laws came down from on-high, making life more and more difficult for the Protestants of Graz and beyond through onerous tax regimes and countless other new restrictions and regulations. On September 20, 1598, the hammer really fell. All active Protestant evangelizers in Graz — meaning those who worked in any capacity for Protestant churches and schools — were told that they must leave the town within fourteen days. Any who chose to remain after that deadline would be subject to arrest.

Oddly, though, Johannes Kepler was spared. Even as his school was being shut down and his colleagues going into exile, he petitioned Ferdinand for an exemption, and was granted one. He was allowed this rare privilege because he was an astronomer and astrologer of growing note, who might be able to bring luster to his town and his archduke. In addition, he was known for the mildness of his rhetoric when it came to religion, a rarity on a continent where both sides loved nothing more than to accuse the other of being fully aware, fully complicit minions of Satan. As Kepler put it, “I am fair and just toward the followers of the pope and recommend this fairness to everyone.” (This stood in marked contrast to his attitude toward right and wrong in empirical disciplines like astronomy.) Kepler’s reprieve came directly from the desk of Ferdinand: “His Highness is herewith granting, out of special favor, that the petitioner, notwithstanding the General Dismissal, shall be allowed to remain here. But he shall maintain appropriate modesty everywhere, so that his exemption will not be subject to cancellation.” Ferdinand may have hoped to convince Kepler in time to convert to Catholicism, perhaps having been led to believe by his reluctance to condemn the alternative vision of Christianity that his Protestantism was only skin-deep, a coat of convenience that he could easily shed for another.

If so, this was a profound misreading of the man. For all that he was unusually tolerant of the religious choices of others, Kepler was also unshakably committed to his own Protestant faith. Life in Graz became harder and harder for him as a result. He had lost his job as teacher with the closing of his Lutheran school, leaving him dependent on his wife’s dowry as his only source of income; this did nothing to improve the harmony in his household. It was gradually becoming illegal not only to preach Protestantism but to be a Protestant, even in the privacy of one’s own home. People on the streets of Graz were subject to random searches by the royal guards, who looked always for that totem of the Protestant faith, a Bible written in German rather than Latin. Kepler holed up in his house, taking refuge in his studies and correspondence. He couldn’t bring himself to beg for help from the great Tycho Brahe, who had himself recently become an exile, but he did petition his old colleagues at the University of Tübingen for a position, only to be peremptorily informed that there were none available. His situation was becoming more and more urgent. He sensed that Ferdinand’s exemption wouldn’t last much longer, as the religious crackdown became ever more extreme and he failed to convert to Catholicism.

Then he got lucky. His stroke of luck was not, as you might be expecting to see me write, a letter from Tycho Brahe offering Kepler the opportunity to come to Benátky and become his protégé. This letter had actually not yet reached him when, in the same December of 1599 when Tycho sent it, one Johann Friedrich Hoffman, a baron in the court of Holy Roman Emperor Rudolf, passed through Graz on his way back to Prague from Rome on some imperial business. Hoffman kept up with developments in the field of astronomy, and knew something of Kepler and his book. Like his emperor, he was nominally a Catholic, but was more interested in encouraging peaceful coexistence between the two versions of Christianity in the empire than he was in enforcing dogma. Hearing of Kepler’s unfortunate situation, and knowing that Tycho Brahe, Rudolf’s new Imperial Mathematician, thought quite highly of the young astronomer, Hoffman offered to take him back to Bohemia with him in his carriage to meet the great man.

Kepler jumped at the chance. Telling his wife that he would send for her and his stepdaughter if and when he was able to settle himself in Bohemia, he prepared for the next phase of his life. On the very first day of the new century — January 1, 1600, by the new reckoning of the Gregorian calendar — he joined Hoffman in his elegant four-horse carriage, surrounded by the guards and attendants that were standard with such an imperial procession. A grimacing Archduke Ferdinand gave Kepler his hand in farewell, likely wishing he had come down much harder on him much sooner. As it was, though, Johannes Kepler was passing out of his control, toward a future which would see his name literally written in the stars.

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(A full listing of print and online sources used will follow the final article in this series.)