by Dan Falk
Thomas Digges was twenty-six when the new star of 1572 lit up the skies over England (the same star observed in Denmark by Tycho Brahe). Digges first noticed the star on November 17—six days after Tycho—and began to study the object carefully. The following year he wrote a short treatise on it. His opinion was in great demand; even the queen sought out his views on the new star. Astrological prognostications aside, Digges believed his observations could be used to test the Copernican theory. His own book about the star, Alae seu scalae mathematicae (Mathematical Wings or Ladders), appeared in 1573, before the star had faded from view. Like Tycho, Digges had managed to measure the parallax of the new star, or, more precisely, to determine that it displayed so little parallax that it must lie much farther away than the moon.
For Digges, measurements of parallax were more than just a clever substitute for a celestial yardstick. The data could also reveal which view of the cosmos—the Ptolemaic or the Copernican—was correct. That’s because the distance between the Earth and the other planets (especially Mars) varied by a much larger amount in the sun-centered scheme than in the geocentric picture. With precise enough observations, one ought to be able to settle the matter. Digges was lucky to have access to the best instruments in England, including a ten-foot cross-staff, for measuring celestial angles, devised by a man named Richard Chancellor; when Digges was a young man, he and Dee used the instrument together. We know that Digges was leaning toward the Copernican theory, and certainly admired Copernicus as the greatest observer of his age. Along with his own measurements of the new star, Digges included a data table with the positions of thirteen reference stars in the constellation Cassiopeia, “taken from Copernicus (with the printer’s errors corrected).” He also confessed to working quickly in case “by order of the Most Powerful, it [the star] should recede again.” The star did indeed fade in intensity over the next few months. By February 1574 it had finally disappeared from view. Yet interest in the strange apparition continued. Like Tycho, Digges was keen to read everything that astronomers throughout Europe had written about the wondrous new star.
“A LETTER SENT BY A GENTLEMAN OF ENGLAND”
Given that this was nearly four and a half centuries ago, one might imagine that fresh evidence concerning Digges and the new star would be rather unlikely to turn up. A few years ago, however, a British historian named Stephen Pumfrey stumbled across a published letter, apparently written by Digges, on the subject of this very star. The document, which does not give the author’s name, is titled “A letter sent by a gentleman of England, to his frende, containing a confutacion of a French mans errors, in the report of the miraculous starre now shyning.” Only one copy of the letter, published in 1573, seems to have survived. It had been dwelling, virtually forgotten, in the library in Lambeth Palace in London. In a journal article published in 2010, Pumfrey presents a compelling case for Digges being the author.
The letter was written in response to another letter, written by another anonymous individual—how much simpler life would be if people signed their names!—living in France.* The Frenchman is identified only by his (presumably Latin) initials, I.G.D.V. Pumfrey suspects this was the work of an astronomer named Jean Gosselin, who worked in the library of the French king, Charles IX. (As Pumfrey admits, the whole business is a mystery “fit for an Umberto Eco novel.”) We know that the French publication dates from 1572. Obviously rushed into print, it has several pages of observations of the new star, as well as a diagram showing its location. But it is deeply flawed: The author identifies the object as a comet, and states that it displayed a significant parallax.
The Frenchman’s letter also provides one of many indications of the profound astrological significance associated with the new star. Although some saw it as a good omen, many feared it was a sign that something ominous was on the horizon—perhaps war, an ever-present danger. That was certainly true in France, a nation already torn by religious strife. Gosselin saw the new star as a sign that God would soon seek out and punish the sinful. He prayed that it would lead people to “mend their bad ways, and in the times to come to live in accordance with the holy law, in the Catholic faith.” Both Tycho and Digges were similarly concerned with the star’s astrological significance, which was widely debated in the royal courts of Europe. Were it truly a new star, it would (they believed) be the first since the birth of Christ, when a bright “star” was said to have led the Wise Men to Bethlehem; another such star, it was imagined, might be a sign of the coming Apocalypse. Such beliefs were widespread at the time, particularly by English Puritans, and were likely shared by Digges himself. As late as 1638—more than sixty-five years after the star had faded from view—an English poet named Francis Quarles was still describing the event from a biblical perspective. In one of his epigrams, he draws a parallel between Tycho’s nova and the Star of Bethlehem:
Both showed them light, and showed their blindness too.
But why a star? When God doth mean to woo us,
He useth means that are familiar to us.
Back to 1572, and Gosselin’s letter: The English ambassador in Paris, Sir Francis Walsingham, obtained a copy and forwarded it to Sir Thomas Smith, one of the queen’s senior advisors. Smith consulted with various Englishmen, including Digges, and wrote back to Walsingham, noting that “your astronomers and ours differ exceedingly” in the observation and interpretation of the new star. Because of the similarities between Smith’s letter and the (presumed) Digges letter, Pumfrey concludes that Smith’s letter was based on conversations with Digges.
Digges’s response in the “Letter sent by a gentleman” is significant, Pumfrey argues, because it is the earliest document clearly revealing his support for the Copernican system, including the Earth’s annual motion around the sun. However, Digges was not the first English scientist to take note of Copernicus’s theory; as mentioned in the introduction, that honor belongs to Robert Recorde, and we’ll take a closer look at his work in the next chapter. But Digges was the first Englishman to have been convinced of the validity of the Copernican model, a conviction that we now know he held as early as 1573. The “Letter sent by a gentleman” reveals something else: It highlights Digges’s religious views, and once again illuminates the complex relationship between faith and “science.” The letter also shows Digges’s interest in the biblical “end times,” believed by many to be close at hand. (For a true believer, of course, this was something to be welcomed rather than feared.) While criticizing the Frenchman’s science, Digges agrees with the conclusion; the new star was “a forewarning of Gods inscrutable pleasure” and a “rare and supernaturall” sign.
The new star eventually receded from view; the apocalypse, if one was expected, failed to materialize. Life went on. But our picture of the universe would never be the same. No wonder the appearance of “Tycho’s star” is often described as a pivotal moment in the history of astronomy. Breaking glass seems to be the metaphor of choice: Timothy Ferris says that the shock it dealt to the established worldview “could not have been greater had the stars bent down and whispered in the astronomers’ ears”; Dava Sobel writes that “one could almost hear the tinkle of shattering crystal”; Dennis Danielson says that “we can almost hear the cracking of the foundations of medieval cosmology.” Those who wanted to cling to the universe of Aristotle and Ptolemy may have dismissed the Copernican model of the solar system as a mathematical convenience, but there was no escape from the implications of Tycho’s new star, observed by skywatchers across Europe and now proven to lie in the supposedly immutable heavens.
* * *
As the learned astronomers of Europe struggled to understand the new star, yet another cosmic surprise appeared, once again in November—a celestial sight now known as the Great Comet of 1577. (Tycho is said to have been fishing when he first caught sight of it.) The comet remained visible throughout the fall and into winter. Because most astronomers of the time were also astrologers, its appearance, like that of the new star, was seen as a
portent. Indeed, comets had a long track record for disturbing the peace. They were often linked to disasters; the word “disaster” comes to us from the Latin dis-astra, “against the stars.” The comet, like the new star, was too far away to be a terrestrial phenomenon. Tycho’s keen observations showed that it was at least as far away as the planet Venus.
Thanks to his work on the new star, Tycho had become famous—and was recognized by the king of Denmark, Frederick II, as a national treasure. The king approached Tycho with a remarkably generous offer: He could have his very own island from which he could conduct his observations. (He would also have the tenant farmers’ rent as his income, adding to his already substantial personal fortune.) The island, Hven (now known as Ven), lies in the channel between present-day Denmark and Sweden. On Hven, Frederick assured Tycho, “you can live peacefully and carry out the studies that interest you, without anyone disturbing you.… I will sail over to the island from time to time and see your work in astronomy and chemistry, and gladly support your investigations.” Tycho gratefully accepted.
THE LORD OF URANIBORG
Tycho would soon transform the three-mile-long island into Europe’s foremost center of astronomical learning. Within a few months, Tycho and his assistants were observing the sun, moon, planets, comets, and stars. They invented new tools for astronomy and mapmaking, and used their own printing press to share their findings with the world. Learned young men from across the Continent descended on Tycho’s laboratory, known as Uraniborg (“heavenly castle”); he referred to these young assistants as his familia. They were eager for a chance to work with the famous observer, even if they snickered behind his back at his deformity (as a twenty-year-old student, he had lost a good part of his nose in a duel; he wore a silver prosthetic, and was continually adjusting it and applying ointments to it). Among his visitors, incidentally, was King James VI of Scotland, who would eventually, on Elizabeth’s death, assume the crown of England as James I.
Sadly, Tycho’s castle no longer stands. But we know from numerous drawings that it was built in the grand style of an early Renaissance palace, with turrets, buttresses, and grand stone archways. As impressive as it must have been, it was not, in fact, very well suited for precision astronomy. Its platforms proved unsteady, and Tycho’s instruments shook in high winds. And so he built a second observatory just down the road. It was known as Stjerneborg (“Castle of the Stars”), and its belowground foundations provided the steady support that his quadrants and large-scale sextants required. (Stjerneborg’s foundations can still be seen today.) Tycho’s most impressive instrument was his giant “mural quadrant.” With a radius of more than six feet, it was oriented exactly north-south, and occupied an entire wall. Because of its size, it could not be turned—but as the Earth rotated, various celestial objects could be tracked. A star’s altitude could be measured to a resolution of ten seconds of arc—that’s about one-twentieth of the apparent size of the full moon. (The mural quadrant, like so many wooden instruments of the period, has not survived.)
Tycho’s island was, in a sense, the world’s first great scientific laboratory—a place where men could devote their lives to the study of nature, never wanting for expertise, equipment, or funds. The endeavor is said to have cost the king one ton of gold; historians estimate that the project absorbed between 1 and 1.5 percent of the Danish national budget. Yet it was more than just a place of scholarly learning. With its grand architecture, orchards, fish ponds, and aviary, it was also a place of sublime beauty. As historian John Robert Christianson describes it, “This was truly a microcosm, offering beauty, harmony, health, and delight to all the senses, for the abundance of the world was here: If ever it were possible to know the Creator through his Creation, this was the place.”
Tycho spent more than twenty years on Hven. During this time, he and his assistants plotted the positions of 777 stars. For historian of astronomy Owen Gingerich, the sheer magnitude of Tycho’s work became apparent during a visit to a Paris bookshop. An obscure volume, published in the mid-1600s, attempted to list all of the observations of the sun, moon, and planets recorded up to that time. The pre-Tychonic observations take up about ninety pages, and those carried out after Tycho occupy another fifty. Tycho’s own observations fill the nine hundred pages in between. Without his contribution, the hefty book would be a mere novella. “The contribution, the sheer bulk of the observations that Tycho Brahe made, is staggering,” Gingerich says. Tycho’s detailed observations of the heavens would provide the most accurate stellar and planetary measurements carried out prior to the invention of the telescope.
One of the highlights of Tycho’s tenure on Hven was the appearance of yet another comet, in 1585. Once again, it was too distant to be sublunar. How could these celestial bodies move to and fro in the heavens, seemingly passing right through Aristotle’s crystalline spheres? As he ruminated over the structure of the heavens, he began to imagine that these spheres had simply never existed in the first place: Perhaps the planets simply moved through space unsupported and untethered.
A CELESTIAL COMPROMISE
One might imagine that, having pulled the rug out from underneath medieval cosmology, Tycho would have been eager to embrace the Copernican model. He had certainly read De revolutionibus, and greatly respected Copernicus. In 1574–75, he gave a series of lectures at the University of Copenhagen in which he expounded on the Copernican system, referring to its creator as “the second Ptolemy.” But for Tycho it was too great a leap to imagine the Earth hurtling through space. Common sense showed that the Earth was stationary; he also took scriptural arguments against a moving Earth seriously. Plus, he was a committed Aristotelian; he believed that there was an unbridgeable divide between the earth and the heavens. And then there was the absence of stellar parallax, hinting, in the Copernican view, at a much larger cosmos—which Tycho was unwilling to accept.
And so Tycho developed a kind of compromise, a hybrid system that had some of the advantages of the Copernican system while keeping the Earth stationary at the center of the cosmos. In Tycho’s model, the planets revolved around the sun, but the sun (along with the moon) revolved around the Earth (see figure 3.2). One might call it geoheliocentric—but that’s a bit of a mouthful; “Tychonic” will have to do. As in the ancient Ptolemaic system, the sphere of the fixed stars defined the outer periphery of the universe; and, again in keeping with the ancient model, the stars revolved around the Earth every twenty-four hours. But Ptolemy’s crystalline spheres were no more; the planets and the sun moved freely, through empty space. Mathematically, the Tychonic system is virtually identical to both the Ptolemaic and Copernican systems, but physically it is quite different.
Tycho had been considering this model for some time, but had worried about the paths that the planets appear to take. Those paths, as can be seen in the figure, intersect—which would be problematic so long as each planet was fixed to its own rigid, crystalline sphere. But his observations of comets had finally forced him to the conclusion that there were no such spheres after all. The planets were free to move through empty space, “divinely guided under a given law.” The spheres, he wrote in 1588, “which authors have invented to save the appearances, exist only in the imagination in order that the motions of the planets in their courses may be understood by the mind.”
The appeal of Tycho’s system would gain wider currency with the invention of the telescope; many of the early observations carried out by Galileo clearly supported the idea that the planets revolved around the sun rather than the Earth. Yet one could still argue that the Earth itself remained stationary while the sun, with its cohort of planets, circled the Earth—as Tycho had suggested. And so, well into the early years of the seventeenth century, Tycho’s system seemed to present a viable alternative to that of Copernicus.*
Fig. 3.2 Not quite Aristotelian, not quite Copernican: In this “hybrid” model of the cosmos, developed by Danish astronomer Tycho Brahe, the planets revolve around the sun, while the sun in tur
n revolves around the earth, which remains fixed at the center of the universe. The Granger Collection, New York
And yet for Tycho himself there was a clear distinction between the aims of astronomy and those of physics. He sought to show how the planets moved; why they did so, or what they were composed of, was another matter:
The question of celestial matter is not properly a decision of astronomers. The astronomer labours to investigate from accurate observations, not what heaven is and from what cause its splendid bodies exist, but rather especially how all these bodies move. The question of celestial matter is left to the theologians and physicists among whom now there is still not a satisfactory explanation.
In other words, Tycho saw his job as answering the “how” and “where” questions: How did celestial bodies move across the sky? Where must one look for them? The question of “why” they moved in such a manner was best left to—intriguingly, from a twenty-first-century perspective—physicists and theologians.
Tycho first put forward his model in 1588, but this work was distributed only to a small number of fellow scientists—a group that included the Englishmen Thomas Savile, John Dee, and Thomas Digges. It would reach a wider audience when formally published, posthumously, as part of his Astronomiae Instauratae Progymnasmata (Exercises for the Reform of Astronomy) in 1602.
Life on Tycho’s island began to sour when a new, budget-conscious king, Christian IV, came to power. In 1599, Tycho took a position in Prague under the patronage of Emperor Rudolf II. His career was winding down, though he was still keenly interested in matters of astronomy. He continued his astronomical observations in Prague, where he soon heard of a brilliant young German mathematician named Johannes Kepler. Tycho invited Kepler to join him, and the two men collaborated until Tycho’s untimely death, in 1601. The story, which has passed into the folklore of science, is worth repeating: One day, Tycho was invited to a dinner party hosted by one of Prague’s most important noblemen. Partway through the dinner, Tycho, who had been drinking “overgenerously,” realized he had to go to the bathroom. Rather than excuse himself from the table and risk offending his host, he held it in, showing “less concern for the state of his health than for etiquette.” (The description comes from Kepler, commenting on the final page of Tycho’s astronomical logbook.) Eleven days later, the fifty-five-year-old Tycho, who was likely already suffering from prostate problems, was dead. His ornate tomb can be seen in the Church of Our Lady before Týn in Prague’s Old Town Square.