The Dog, the Bear, and the Nose

Written by Bryce Bonnet

The partnership of astronomers Tycho Brahe and Johannes Kepler was one of the most successful and distinguished scientific collaborations of all time. Although they only worked together for one year, Tycho’s massive data compilation and Kepler’s outstanding mathematical expertise led to several groundbreaking theories such as the Planetary Laws of Motion and the refutation of the Ptolemaic System (Christianson). However, this partnership almost never happened, thanks to a long-standing feud between Tycho and a German astronomer named Nicolaus Reimers Bär (1551 – 1600). With egos almost as grandiose as their astronomical discoveries, the relationship between the three men came to define Tycho’s final years and Kepler’s early career.

Kepler Mysterium plate 3By 1597, Johannes Kepler was a young mathematics teacher who had just made a name for himself in astronomy. He had published the Mysterium Cosmographicum just two years before, in which he proposed that the structure of the universe was geometrically composed of Platonic solids. While the theory proved to be incorrect with time, the book’s brilliant equations and philosophical simplicity earned the approval of both astronomers and theologians. Kepler, desperate for a job and money, had begun sending the book to several prominent scientists along with many letters of praise and flattery (Ferguson). One such copy fell into the hands of Nicolaus Reimers Bär, an imperial mathematician who worked under the Holy Roman Emperor Rudolf II. Bär, often referred to as the Latinized “Ursus” or “Bear,” had recently written On Astronomical Hypotheses, in which he proposed a new astronomical system in which the sun and the moon rotate around the earth with all other planets rotating around the sun. Ursus, wanting legitimize his theory with a preface of a relatively well-known author, began his book with an adulatory statement written by Kepler that praised Ursus’s genius.


Nicolaus Reimers’ 1588 geo-heliocentric planetary model. From Fundamentum Astronomicum (1588). Wikimedia Commons.

While under normal circumstances this would appear to be an incredible breakthrough for Kepler in the scientific community, he had unwittingly attached himself to a work of plagiarism. The “revolutionary” system that Ursus had proposed was almost completely identical – sans a few details – to the Tychonic System theorized by Tycho Brahe many years prior. “On Astronomical Hypotheses” was not only a work of plagiarism, however; Ursus had gone out of the way and made a “scurrilous personal assault on [Tycho] and his family” by mocking Tycho’s nasal disfigurement and his family’s commoner status (Ferguson). Tycho’s first introduction to Kepler was through this scandalous book, where he read Kepler praise Ursus as the “rank first of the mathematici of our time like the sun among minor stars.” Fortunately for Kepler, the next book Tycho happened to pick up was Kepler’s own Mysterium Cosmographicum, in which Kepler praised Tycho as the “prince of mathematicians not only of our time but of all times” (Ferguson). Tycho, who was familiar with adulation and not necessarily sincere rhetoric was most likely amused that Kepler’s ranking placed him somewhat above his rival.


Tychonic System. Wikimedia Commons.

The bitter feud between Tycho and Ursus can be traced back to 1584, when Ursus visited the Uraniborg Observatory as a young surveyor. The two men could not have been more different in terms of background; whereas Tycho was of noble birth and was raised with a comprehensive education, Ursus was a lowly pig herder until the age of 18 and was entirely self-taught (Launert). Despite these differences, both were very intelligent, knew several languages, and were intensely curious about astronomy and mathematics. Indeed, many historians believe that Tycho admired Ursus’s intellect and was interested in hiring him as an assistant to work at Uraniborg. However, relations between the two soured when it became apparent that Ursus was more interested in nosing through manuscripts and examining instruments than working with Tycho. Tycho and his assistants became suspicious of Ursus, and began to worry that Ursus might have seen the yet-unfinished Tychonic System (Christianson). Shortly after this visit, Ursus began to speak of a new planetary model that he had devised, and distributed mechanical models of this “Bär System” to Danish and German nobility. Paranoid that Ursus was planning to exhibit the Tychonic System as his own creation, Tycho hurriedly finished a manuscript that described a decade of research on the island of Hven. Over the next few years, the two scientists published several texts and rebuttals against each other, with each trying to prove that they were the originator of the system. This caused a brief controversy where Tycho insisted that he had discovered a parallax for Mars in 1582, even though he hadn’t even attempted the observation until 1587, and had achieved no conclusive results (Ferguson). Although Tycho avoided lasting damage to his reputation, the affair proved to be immensely embarrassing for him. Ursus had made himself an enemy of Tycho, and the bitterness between the two lasted for the rest of their lives.

Over the next ten years, the two men’s fortunes drastically changed. Ursus became a renowned scholar after serving in the court of the Landgrave of Hesse-Kassel and translating a work of Copernicus into German, and was appointed imperial mathematician to Emperor Rudolf II (Launert). Tycho, on the other hand, had been subject to several misfortunes; unable to sway the newly appointed Danish King Christian IV to continue to support his pursuit of science, Tycho was subjected to attacks by personal enemies he had gained over the years and was exiled from the country. After several years living abroad, Tycho and his family were granted patronage from Rudolf II and settled in the Austrian (now Czech) city of Prague. As convenient as this was for Tycho, this brought him back into Ursus’s sphere of influence, and he was still highly paranoid and resentful towards Ursus. Fortunately for Tycho, Ursus had fallen out of the emperor’s favor due to his inability to back his “Bär System” with logical reasoning or data (Rosen). Tycho would appeal to the emperor, who decided to appoint him as his next imperial mathematician. With his newfound job and patronage, Tycho could live luxuriously and resumed his scientific observations in Prague. It was here that Tycho read the Mysterium Cosmographicum, and was impressed enough with Johannes Kepler’s work to invite him to come work at Emperor Rudolf’s court.

Kepler was in his late twenties by time he started working for Tycho. Although obviously very intelligent, Kepler was somewhat hindered by a low self-esteem and a desire to please in his early career. He had once humorously described himself as a “dog,” and noted that he “continuously sought the goodwill of others” (Ferguson). Even though he earned acclaim for his work, very little of it could mend a personal life that was continuously plagued by tragedy; his first few children died in childbirth, he was held in poor regard by his parents-in-law, and his first marriage with Barbara Müller was considered unhappy. He lived through his scientific research, and the opportunity to communicate and work with one of the most pivotal astronomers of the time was no doubt an exciting experience. However, Tycho was not willing to let Kepler off the hook immediately; as impressed as he was with Mysterium Cosmographicum, he still remembered Kepler’s earlier correspondence with Ursus. Tycho and Kepler’s early letters were cordial, but Tycho was fully aware of his advantage over the blooming astronomer. He made sure to keep Kepler in place by reminding him that his theories were not entirely convincing, and that he had made a grievous error by praising Ursus.

As the sixteenth century ended, Tycho became increasingly cognizant of his diminishing abilities. Now in his late fifties, Tycho was still master of his craft, but his observations were less frequent. Along with this, Tycho was unwilling to forget about Ursus. He became paranoid that his assistants – especially Kepler – were agents of Ursus, and that they were out to steal the data from his observations. When Kepler came to work at Emperor Rudolf’s court, he was assigned to work on the Mars orbit. Although grateful, Kepler still felt as though he should have had access to all Tycho’s data, as opposed to the data for just one planet. He also felt constricted, as he wanted to test the data with the Copernican System as opposed to just the Tychonic System. Nevertheless, Tycho and Kepler continued to work compatibly together, with Tycho praising Kepler’s writing ability and his “well-rounded way of expression” (Ferguson). He later used Kepler’s ways of “expression” to begin writing the “Quarrel between Tycho and Ursus,” which included a detailed history of the feud between the two and how Tycho’s theories were ultimately superior to Ursus’s. He was hoping to build a case against Ursus, and to hopefully finish him off – even though he had lost his influence long ago. By 1600, Ursus’s health was failing, and he passed away before Tycho could pursue any legal action against him.

Although his nemesis had perished, Tycho was not so interested in “destroying the person” as he was in “destroying [his] book [of] insults and lies” (Ferguson). He ordered Kepler to continue writing against Ursus, even though Kepler himself found it distasteful to carry on the dispute after his death. Tycho was resolute with this issue; he would not be completely satisfied until he not only destroyed Ursus’s credibility as a scientist and claimed the Tychonic system as his own, but also discouraged others from plagiarizing his work. Though this old man’s obsession was most certainly a poor assignment for Kepler, the “Defense of Tycho against Ursus” proved to be one of his greatest works, with Ferguson claiming it was “one of the finest analyses ever written about scientific methodology.” It had allowed Kepler to fully pursue his grievances against the Ptolemaic System, arguing that although they are as accurate as the Copernican System, the “physical motions could no longer hold their own” (Catton). These criticisms applied to the Tychonic System as well.


Frontispiece of the Rudolphine Tables. The image celebrates the great astronomers of the past: Hipparchus, Ptolemy, Copernicus, and most prominently, Tycho Brahe. Wikimedia Commons.

Finally, after Ursus had been dead for nearly a year, Tycho finally opened himself to Kepler, allowing him access to all his recorded data. Tycho and Kepler would work together to create the Rudolphine Tables, which would compile all Tycho’s observations into the most accurate astronomical readings the world had yet to know. Tycho appealed to Emperor Rudolf to grant his assistant a salary for Kepler, which was quickly granted (Ferguson). With Kepler’s financial woes solved and Tycho willing to open up to his student, a prodigious partnership was destined to lead to incredible discoveries. Unfortunately, in late 1601, Tycho passed away from uremia, leaving Johannes Kepler to carry on Tycho’s immense duties as one of the world’s most foremost astronomers.

The partnership between Johannes Kepler and Tycho Brahe was one of the most interesting in the history of science, but it’s surprising how much of it was spent dealing with Nicolaus Ursus. Although mostly cut short by Tycho’s death, it’s strange to think that at least three of the four years Tycho and Kepler spent working together were hindered by Tycho’s paranoia, and it’s tempting to think of what could have been achieved between the two otherwise. All three men were geniuses, but their intellect and egos were so strong that what could have been achieved through cooperation was for many years delayed by petty squabbling. Had Ursus been willing to work with Tycho from the beginning, it’s probable he could had reached the same level of fame and prestige as Kepler. Perhaps if Tycho wasn’t so paranoid about plagiarism, he and Kepler could have accomplished even more than their short partnership gave mankind.

Works Cited

Catton, Philip. “The Birth of History and Philosophy of Science: Kepler’s Defense of Tycho against Ursus with Essays on Its Provenance and Significance. N. Jardine.” Philosophy of Science 53.3 (1986): 453-55.

Christianson, John Robert. On Tycho’s Island: Tycho Brahe, Science, and Culture in the Sixteenth Century. Cambridge: Cambridge UP, 2003.

Ferguson, Kitty. Tycho & Kepler: The Unlikely Partnership That Forever Changed Our Understanding of the Heavens. New York: Walker, 2004.

Launert, Dieter. “Nicolaus Reimers.” Omics Internationl. Omics Publishing Group,

Rosen, Edward. Three Imperial Mathematicians: Kepler Trapped between Tycho Brahe and Ursus. New York (N.Y.): Abaris, 1986.