The Theory of Heliocentrism

On the evening of November 11, 1572, a Danish nobleman and natural philosopher by the name of Tycho Brahe was walking home in Scania, a province at the southern tip of modern-day Sweden which was then a part of Denmark. The 25-year-old Tycho was tired and dirty, having worked all day in an alchemical laboratory, experimenting with Venetian glass-blowing techniques and dreaming of discovering the mythical philosopher’s stone that could turn base metals into gold. At this point in time, he had in mind only a hot supper and a warm bed. And then he looked up and gasped.

Tycho was a seasoned observer of the night sky, who had nursed a passionate interest in astronomy and its then equally respectable partner discipline of astrology ever since witnessing a partial eclipse of the Sun at age thirteen. By now, he knew the constellations as well as he did his own face in a mirror. Like almost all of the other natural philosophers of his time, he was highly invested in the notion of a clockwork universe of God-given regularity, order, and permanence. In fact, this belief was precisely what made the sight he saw above him now so shocking: not far from the familiar constellation of Cassiopeia, he saw a bright new star where none had been before.

His vision of the cosmos had no place for a new heavenly body that simply appeared out of nowhere from one day to the next. His first instinct was to wonder if he was hallucinating, perhaps as a result of all of the alchemical fumes he had breathed in that day. He rushed home to ask his servants to look up and tell him if they too could see the bright new star. They could. He would later write how

when I pointed out the location and learned that others could see it, I no longer doubted that a star actually appeared there. This was truly the greatest miracle in the whole of nature since the beginning of the world. All philosophers agree, and reality itself declares unambiguously, that no alternation of generation or corruption occurs in the ethereal regions of the heavenly world, but that the heavens and the ethereal bodies therein neither increase nor decrease in number, magnitude, luminosity, nor in any other way, but are always the same and always will be the same, never worn down by the years, permanent.

All of that, it seemed, had just been thrown out the window. Alchemy was forgotten; the life of Tycho Brahe would be consumed by this bright new star for the next year and a half, until it disappeared again as inexplicably as it had appeared.

He was not alone in his fascination. All of the people of Europe, from kings to peasants, were preconditioned to read divine signs and portents in the sky. A development as singular as this had to have an earthshaking meaning. Catholics saw it as a sign of God’s displeasure toward the Protestants who had chosen to deny the holy authority of the pope; Protestants saw it as a sign of his displeasure at the venality and corruption of the all too earthly man and institution that presumed to speak in God’s name. All wondered whether it was a harbinger of the long-delayed Apocalypse of the Book of Revelation.

Tycho, however, was uniquely positioned to do something more than look up and speculate. For he had already made important strides toward returning astronomy to its ancient roots as an observational, empirical discipline. Most of his peers of the present and immediate past — including one Nicolaus Copernicus — spent surprisingly little time taking the measure of the heavens for themselves. They were content to work from the observational data provided by ancient demigods like Hipparchus and Claudius Ptolemy, using mathematics alone to try to draw new connections and spin up new models on the abstract canvas of the imagination. Tycho Brahe, by contrast, was a hands-on man, whose instinct was always to see and verify for himself. He had started to keep a meticulous journal of his astronomical observations in 1563, when he was just seventeen years old. He would continue to do so for the rest of his life.

Almost as soon as he began to look up for himself in earnest, the teenager had noticed discrepancies between where his books said the heavenly bodies ought to be on any given night and where they really were. On August 23, 1563, he saw Jupiter and Saturn reach a conjunction with one another, meaning that they crossed one another’s paths in such a way that they briefly looked like one planet, spectacularly bright. This was exciting, but also dismaying for the precocious young Tycho, for this event occurred in reality a day before when his books said it should. Many an astronomer might have been inclined to forgive his ancient forebears an error of one day across a gap of well over 1000 years, but not Tycho Brahe. He concluded that the extant books of astronomy “suffered from intolerable errors.” The only solution was to roll up his sleeves and take measurements for himself.

He built his first astronomical instrument the following year, a handheld gadget called a Jacob’s staff that he used for measuring the altitude of stellar objects above the horizon in degrees. Seeking greater accuracy, he then moved on to quadrants. His early masterpiece came in the form of his massive Quadrans Maximus (“Great Quadrant”), which had a radius of eighteen feet (5.5 meters) and was, so he claimed, accurate to within .003 degrees.

But the young Tycho’s life wasn’t all astronomy. He was also experimenting with alchemy, becoming fluent in Latin and several other languages, reading the law, writing horoscopes and poetry, and drawing up architectural plans. A true Renaissance man, he was well on his way to becoming Scandinavia’s nearest answer to Leonardo da Vinci. He was the farthest thing from a cloistered recluse like Copernicus; Tycho was a big, robust man who loved a good party and never shirked from a brawl. When he was twenty, he had most of his nose sliced off in a drunken midnight sword fight in the German town of Rostock. He would wear a painted brass or silver prosthesis on his face, held in place by glue, for the rest of his life. Adhesives not being terribly advanced at this time, it had a tendency to fall off when he laughed too heartily — a disconcerting sight indeed for his fellow party-goers.

Yet all that had come before in Tycho’s life now seemed to him like mere preparation for the arrival of this new star. It was at its brightest on the night when Tycho first saw it, then proceeded to very slowly fade away over the seventeen months that followed, until it disappeared entirely in March of 1574. Sensing from the start that time was limited, Tycho studied it endlessly, obsessively,  using every instrument his clever mind could come up with and his skillful hands could build. In particular, he looked for the slightest sign of motion, in order to know whether the new star should be classified as one of the fixed stars of the heavenly sphere or as an addition to the seven wandering heavenly bodies. He concluded that it was stationary.

The new star was still slightly visible when Tycho published a book about it, entitled simply De Nova Stella (“On the New Star”). It’s an odd book, not at all what we expect a scientific text to look like today. It opens with a lengthy dialog between Tycho and Jason Pratensis, a Dutch scholar and friend, over whether he should be writing the book at all; in many European circles, authorship was still considered beneath the dignity of the nobility. There follow poems from some of Tycho’s other friends and a lengthy “Elegy on Urania” by Tycho himself, betraying the heavy influence of his favorite ancient poet Ovid. There is also much discussion of the potential astrological significance of the new star, which is compared to the Star of Bethlehem foretelling the birth of Jesus. Plopped down amidst it all is the reason we remember the book today: 27 pages of “hard, obstinate facts,” as Tycho described them, detailing his measurements and observations of the new star. This was fresh empirical data, something there had been shockingly little of in European astronomy for a shockingly long time.

We now know that the “new” star Tycho saw was really the death of an old one in an inconceivably gigantic explosion. Borrowing from the Latin title of his book, we still call this rare event a “supernova.”

A supernova is a fascinating topic in itself, but for our purposes today, Tycho’s new star is most important for the way it made his name as the premier astronomer of his time, and how this in turn enabled him to begin to place astronomy itself on a whole new, empirical footing. The beautifully printed and illustrated volume became a sensation — far more of one than Copernicus’s had ever been — and Tycho embarked on the sixteenth-century equivalent of a book tour, lecturing and reveling in the approbation of his various hosts; he was never averse to having his ego stroked. He went to Frankfurt, Basel, Augsburg, Wittenberg, even Catholic Venice (where he had a blessedly better experience than Giordano Bruno later would).

His fame grew so great that King Frederick II of Denmark, fearful of losing him forever to some foreign court or university, made him an extraordinary offer in February of 1576.

I was staying recently at the castle I am building in Helsingør, and when I looked out one of the windows, I saw the little island of Ven, lying in the Sound in the direction of Landskrona. No nobleman lives there. It occurred to me that it would be very well suited to your experiments in astronomy, because it is high and has an isolated location. If you want to live on the island, I would gladly grant it to you. There you can live peacefully and carry out without disturbance the studies that interest you. I see it as my duty to support and promote things like this appropriately. What good would it do for you to return to Germany and live as a stranger in order to accomplish that which you can do just as easily in your native land? We should assure instead that Germans and people of other countries who want to know about such things should come here to see and learn that which they can hardly find elsewhere.

So, Tycho Brahe became the ruler of his own private island, one that would come to seem to its visitors as much a place of magic and mystery as Prospero’s island in The Tempest.

Now a possession of Sweden rather than Denmark, Ven rises dramatically out of the waters of the Øresund, the strait that separates Danish Zealand from the Swedish mainland. Its vertiginous yellow cliffs reach up to a fertile plateau of three square miles (7.5 square kilometers) that was home in Tycho’s day to just one small village, its church, and the villagers’ fields. Tycho moved there with his mistress, Kirsten Jørgensdatter, a commoner whom he adored but was unable to marry due to her low birth; he already had two daughters with her when they made the move. He set about building a home and observatory — a small castle, really — at the very center of the island.

He called this complex Uraniborg. It was partially a villa done in the Italian Renaissance style — a first for Scandinavia — and partially an entirely unique creation. In addition to quarters for Tycho’s family and servants, it included guestrooms of various levels of luxury, a huge library, a private printing press, a paper mill, an alchemical laboratory, an orchard, a game preserve, an aviary, and a fish pond. “Life at Uraniborg was not exactly what one would expect to be the routine of a scholar’s family, but rather that of a Renaissance court,” writes Arthur Koestler. “There was a steady succession of banquets for distinguished visitors, presided over by the indefatigable, hard-drinking, gargantuan host, holding forth on the variations in the eccentricities of Mars, rubbing ointment on his silver nose, and throwing casual tidbits to his fool Jepp, who sat at the master’s feet under the table, chattering incessantly amidst the general noise.” Clearly Tycho Brahe enjoyed being the king of his own private kingdom. As if the court jester wasn’t enough, he also had his own little dungeon built in the basement, into which he cast any of the local peasants who annoyed him. (His relations with the previous residents of Ven were, shall we say, less than harmonious.)

One early evening in November of 1577, Tycho was fishing in his pond, when he looked up at the sky and was stunned to see something completely unexpected there for the second time in his life. Another new star hung in the dusk, brighter even than the last one he had seen, this time seeming to drag a long luminescent tail behind it. He dropped everything else to study it for the next two months, until it disappeared. His observations told him that this tail-dragging star was markedly different from the last new star he had seen in one more way: it was moving across the sky.

What he was seeing this time was a comet, a frozen visitor from deep space that had begun to melt and shed luminescent gas as it was heated by the Sun, until it looped around that body and returned to the empty blackness whence it had come. Such things have shown up from time to time throughout recorded history, usually to be received as messengers sent by the gods or God, harbingers or memorials of some momentous event. In ancient times, comets were believed to have marked the death of Julius Caesar and the defeat of Attila the Hun. Tycho the astrologer postulated that this comet meant that “in the following years will take place great changes and reformation, both in spiritual and worldly affairs, which perhaps will be more to the good than the worse for Christendom,” all leading up to the year 1603, when, so his numerology told him, “the eternal Sabbath of all creatures is at hand.”

Tycho the astronomer, however, made waves by claiming that the comet was a physical object in space, just like the planets, rather than an ineffable  manifestation of divine light, which was the consensus view on the subject at the time. This was a huge can of worms to be opening. For if the cosmos really was an enclosed sphere, the fixed stars points of light imprinted on the inner surface of that sphere, then where had the comet come from? How could it get inside this closed system, and how could it get outside it once more when it disappeared from view, never to be seen again? Tycho didn’t know; he could only report what his observations indicated to be true. As for the rest, “our limited and earthly understanding [provides] no real grounds and knowledge.”

In insisting on the primacy of empirical observation and inductive logic over abstract philosophizing, Tycho was making a bold break with the Aristotelian astronomers, who, he scoffed, picked up their “knowledge and opinions not from experience of any mathematical observation done with assiduous methods, but they have it from subtle arguments of reason alone. However embellished it might be with subtle arguments, [it] is still only a good thought taken from human reason, which can be refuted by other arguments from human reason.” Hard observational data of the sort that Tycho attempted to provide, on the other hand, was irrefutable. It marked the start of a shift in the way that astronomy was done — in what astronomy was in a quite fundamental sense — that would come to full fruition only after Tycho’s death.

There appeared no more totally unexpected sights in the sky to wonder at in the years after the comet, but life and work went on apace at Uraniborg. Tycho was possessed of a titanic ego that manifested itself in such forms as a giant mural that covered one entire wall of his castle, showing the genius surrounded by his many instruments. Everywhere one looked at Uraniborg were clever gadgets, such as a statue of Pegasus that rotated on its own, an automatic sprinkler system to water the gardens, and a system of bells in every room that Tycho could ring at any time from his study; small wonder that many people considered him to be a sorcerer. King Frederick was a regular at his table, and King James VI of Scotland — later to become King James I of England as well — visited on at least one occasion. Tycho entertained all comers in lavish fashion.

Yet this garrulous man of prodigious appetites was capable of the most patient, methodical labor when he stood behind one of his instruments. The historian of science K.P. Moesgaard credits him with “setting a new standard of objectivity in empirical science.” He understood not only the value of accuracy but also that of reproducibility; no measurement was worth anything, he knew, until it had been double- and triple- and quadruple-checked. No person of his own time, and vanishingly few of any other, looked longer and harder at the sky than him.

His most concrete achievement of the two decades he spent at Uraniborg took shape under a great dome that he had constructed there. Here he had painted 777 different stars, each in its proper position, each shining with its proper magnitude. The data he collected on the stars put even Hipparchus to shame — and all of it was collected without benefit of any form of magnification. The tragedy of his life was that he lived just a little too early to have access to the telescope, that most important invention of all in the history of astronomy. Skilled inventor that Tycho Brahe was, what might have happened if he had turned his mind to the study of optics? Alas, the idea seems never to have occurred to him.

Like many of his contemporaries, Tycho praised Copernicus for “restoring the science of celestial motion,” but deemed his heliocentrism to be “contrary to the principles of physics”: “it ascribes to the Earth, that hulking, lazy body, unfit for motion, a motion as quick as that of the aethereal torches.” As a dyed-in-the-wool empiricist, he judged the bulk of his observational data as well — most tellingly, the absence of stellar parallax — still to point to a stationary Earth. And yet, again like many of his contemporaries, he was dogged by a sneaking suspicion that Claudius Ptolemy hadn’t had it right either. The model of the cosmos that he eventually arrived at hearkened back even further than Ptolemy, to the fourth century BC and the ideas of the Greek philosopher Heraclides Ponticus. This system had the Sun and Moon only orbiting the Earth, the five planets orbiting the Sun. It had the virtue of conforming far better to the sixteenth century’s version of political correctness than did Copernicus’s heliocentrism.  Arthur Koestler calls it “a compromise between the Copernican universe and the traditional one. It automatically recommended itself to all those who were reluctant to antagonize academic science, and yet desirous to ‘save the phenomena.'”

But if the model itself was less controversial than full-on heliocentrism, the circumstances of its dissemination came complete with plenty of controversy of their own.

In 1584, well before Tycho publicized his modified geocentric cosmos, he was visited on Ven by Erik Lange, a fellow member of the Danish nobility with a strong interest in natural philosophy, who brought along with him an eager young German mathematician and astronomer named Nicolaus Reimers. For reasons that shall forever remain unknown, Tycho took an immediate dislike to Reimers, whom he referred to only as “Erik’s boy.” When the talked turned to models of the universe, Tycho refused to elaborate on his theories unless Reimers was sent away. Once this was duly done,

I sketched and explained in broad lines the [model] I had worked out myself. Afterward, I wiped it out again as well as I could; I had sketched it on the green cloth that covered the table. But this nosy busybody [Reimers] got a whiff of what we had hidden from him. He sniffed around and gained information about many other things of mine.

This unbecoming curiosity did not please Tycho, who went so far as to send a servant in to search Reimers’s possessions while he was sleeping. This servant allegedly found “four whole handfuls of tracings and writings” that had been copied verbatim from Tycho’s own notebooks. Incensed, Tycho ordered Reimers confined to his quarters for the rest of his stay on Ven.

Four years later, in 1588, the ever-meticulous Tycho had still not published his model of the cosmos; he was still collecting observational data so as to fine-tune its every aspect. That year Nicolaus Reimers, who had by now taken to referring to himself as Reimarus Ursus (“Reimers the Bear”), came out with a book called Fundaments of Astronomy, detailing a cosmic model of his own where only the Sun and the Moon orbited the Earth. In fairness to Reimers, it should be noted that there were significant differences between his cosmos and that of Tycho. In fact, Reimers’s system was actually closer to being accurate than that of Tycho in at least one respect: Reimers said that the Earth rotates as it otherwise stands still, while Tycho believed that it doesn’t move at all.

Nevertheless, Tycho was absolutely convinced that Reimers was nothing but a shameless plagiarist, and didn’t hesitate to share this opinion with the world after he had rushed his own version of the model into print. These two outsized egos would remain fierce, vocal enemies for the rest of their lives, as Reimers became the first man in years to challenge Tycho for the status of the preeminent astronomer in Europe. Holy Roman Emperor Rudolf II named Reimers his “Imperial Mathematician” and invited him to join his court in Prague. It was an amazing leap for a man who had been a lowly swineherd until age eighteen, a tribute both to his talents and to his sheer, brazen chutzpah. A shrinking violet he was not; nor was he a man afraid to mix his martial metaphors. Of Tycho and his boosters, Reimers the Bear wrote that “I will meet them as a bear that is deprived of her whelps, and will rend the caul of their heart, and there will I devour them like a lion. The wild beast shall tear them.” He knew how to hit below the belt — or below the eyes. He wrote that Tycho was equipped to “discern double stars through the triple holes in his nose.”

An aspiring astronomer/astrologer named Johannes Kepler, a teacher at a Protestant school in Graz, Austria,unwittingly wandered into the middle of this minefield of a feud.

In November of 1595, the 23-year-old Kepler, being eager to curry favor with the leading astronomical minds of the day, wrote a fawning letter to Reimers, hailing “the bright glory of thy fame which makes thee rank first among the mathematicians of our time like the Sun among the minor stars.” Reimers didn’t even bother to answer this missive from an unknown striver. But the following year, Kepler published a book of his own, called the Mysterium Cosmographicum (“The Mystery of the Cosmos”). The text was drenched in the hermetic mysticism that was so fashionable at the time, obsessed with Platonic solids and the music of the spheres and taking it as a given that the configuration of the heavens can be read for insights into the mind of God. Still, some of the mathematics attached to all this mystical gilding were clever and interesting. The book raised Kepler’s profile enough that, when Reimers published his latest screed against Tycho in 1597, he pulled Kepler’s old unanswered letter out of his files and included it among a collection of citations that were meant to illustrate how respected the Bear was among his peers.

This was decidedly awkward for Kepler, who, having not received any personal response to his fan letter to Reimers, had in the meantime written a similar letter to Tycho, from whom he had received a polite reply, the beginning of a regular correspondence. Now he seemed to have inadvertently joined Team Reimers, which he no longer wished to be a part of. There are two possible explanations for his preference for Tycho. The less charitable to Kepler is that Reimers’s star was by now descending almost as quickly as it had risen; he had been dismissed from the court of Rudolf II, possibly in response to Tycho’s continued accusations of plagiarism against him, possibly because of his overweening endemic arrogance, possibly for both reasons. The more charitable explanation is that Kepler simply realized for himself that Tycho would be the more practically useful friend when it came to his own studies of the heavens, being possessed of a mass of observational data that was second to none and still largely unpublished; if this is the truth, the decision was still predicated on who could do the most for Johannes Kepler, but in a way that transcended mere careerism. It’s entirely possible, of course, that both explanations were to some extent correct in Kepler’s case as well.

At any rate, Kepler wrote again to Tycho, prostrating himself before his learned better.

How come? Why does [Reimers] set such value on my flatteries? If he were a man he would despise them, if he were wise he would not display them in the marketplace. The nonentity which I then was searched for a famous man who would praise [me]. I begged him for a gift, and behold, it was he who extorted a gift from the beggar. If, in the selfish desire to flatter him I blurted out words which exceeded my opinion of him, this is to be explained by the impulsiveness of youth.

Tycho Brahe was not always one to forgive an insult quickly, but in this case he behaved with admirable graciousness. He accepted Kepler’s explanation and apology, and the old and young astronomer continued their correspondence. Clearly Tycho was impressed by Kepler, perhaps saw something in him that reminded him of his own younger self.

Ironically, if careerism really was first and foremost in Kepler’s mind when he wrote to Tycho to apologize, certain events that were happening in Denmark at the same time as this brouhaha might have given him cause to reconsider, had he only known about them. For the fact was that Tycho as well as Reimers had lost his royal patron. King Frederick II had actually died back in 1588. His son and successor, Christian IV, never took to Tycho like his father had. A boy just ten years old when he officially became king, Christian could do little to act on his antipathy until he came into his majority at age eighteen. When he did, however, he wasted no time in withdrawing from Tycho the royal grant of the island of Ven and the supposedly lifetime stipend that went along with it. Probably not coincidentally, the Protestant church in Denmark began for the first time to seriously complain about Tycho’s conjugal — or rather non-conjugal — state at the same time. (By now, Tycho had no fewer than eight children with Kirsten Jørgensdatter.) Feeling harried from all sides, Tycho expressed himself in verse: “Denmark, what was my offense? How did I hurt you, my native land? Was it wrong to spread your fame abroad?”

But King Christian was implacable in his hostility toward his father’s pet Prospero. So, in the summer of 1597, when he was 50 years old, Tycho Brahe packed up his household, his instruments, and even his printing press and left Ven — and Denmark — forever. Characteristically, his verse now turned defiantly triumphal: “I am no exile, but win a greater freedom. My exile was when I lived in my native land!”

And indeed, Tycho was not without resources. After all, he now overshadowed even Nicolaus Reimers once again as the most famous and respected astronomer in all of Europe. He had good reason to believe that others would be willing to subsidize him if the king of Denmark was no longer interested in doing so. He lived for a while near Hamburg, then moved on to  Magdeburg, Dresden, and Wittenberg, traveling and dwelling always in the most opulent fashion, taking advantage of a succession of generous if temporary patrons. Wherever he stopped, he conducted more observations, published more pamphlets, corresponded as widely as ever, and found the time to be the life of many a party betwixt and between it all.

One day he received a letter from none other than Holy Roman Emperor Rudolf II, asking him to come to Prague for a royal audience. Rudolf was nominally a Catholic, but he ruled amicably enough over many Protestant provinces of Germany. In his heart of hearts, he was probably an agnostic if not an atheist; he attended Mass so rarely that the pope had taken to sending him a personal congratulations whenever he did turn up. In light of this, religious differences shouldn’t prove a difficulty in his relationship with Tycho.

So, Tycho made the trip, arriving in Prague in June of 1599. “I went in to the emperor alone and saw him sitting in the room on a bench with his back against a table, completely alone in the whole room, without even an attending page,” Tycho wrote later. “He promised to support me and my research, all the while smiling in a most kindly way, so that his whole face beamed with benevolence.” Tycho agreed to become the next Imperial Mathematician, a title last held by Reimers. No appointment could have more deliciously demonstrated his return to total ascendancy over his upstart rival.

Rudolf set Tycho up in a small castle in the Bohemian town of Benátky nad Jizerou, about 25 miles (40 kilometers) outside of Prague. Thinking he had found a permanent base of operations as enduring as his castle on Ven, Tycho just as soon as he arrived commenced drawing up plans for an observatory and an alchemical laboratory, on an even more lavish scale than the ones he had built on his private island. In December of 1599, he wrote to Johannes Kepler, who was still living and teaching in Graz. In his letter, he offered this man whom he was now prepared to call his “friend” the opportunity to become his protégé.

You have no doubt already been told that I have been most graciously called here by His Imperial Majesty, and that I have been received in the most friendly and benevolent manner. I wish that you would come here, not forced by the adversity of fate, but rather on your will and desire for common study. But whatever your reason, you will find in me a friend who will not deny you his advice and help. If you come soon, we shall perhaps find ways and means so that you and your family shall be better looked after in the future.

What followed would prove the most significant meeting of astronomical minds since Nicolaus Copernicus met Georg Joachim Rheticus, with consequences that would reverberate down through the new century in precisely the way that Copernicus’s bombshell had never quite managed to do during the last one.

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