Tycho's early astronomical-astrological activity

Tycho's scientific memoir opens with the great conjunction of Saturn and Jupiter of 23 August 1563, when as a sixteen-year-old student he was studying at the University of Leipzig (TBOO 5, 106–107). Since his tutor would not agree with his devotion to astronomical studies he practiced it in secret. Tycho in reconstructing his scientific biography apparently relied on his manuscript observational notes, which start only six days before the observed conjunction (TBOO 10, 3). Although the young Tycho's first observation was obviously motivated by the astrological significance of the event, there is no further astrological analysis in the notes. As he later explains in his life account, the event forced him to realize that his observations coincided neither with the ephemerides based on the Alfonsine Tables nor with those (although in lesser degree) which followed from the Prutenic Tables (cf. TBOO 7, 127–128). One consequence was his early recognition of the need for better instruments, since such failures could be caused by inadequate tools. Before year's end Tycho constructed his first wooden cross-staff, the so-called “Radius Astronomicus,” following Gemma Frisius’ guidelines and Johannes Homelius's instructions in dividing it by transversals. The design of this instrument by Homelius, a former friend of Paracelsus and student of Rheticus, was presented to him by the Silesian Bartholomaeus Scultetus (TBOO 5, 107).Footnote ⁴

In his narrative Tycho recounts the beginning of his career as an observational astronomer aiming at correct observations and improved knowledge of planetary motion. His reference to the Alfonsine and the Copernican tables suggests that his initial problem as a student of astronomy was the failure of both the Ptolemaic and the Copernican solutions, which he would finally resolve in the 1580s (TBOO 7, 127–128). Tycho's self-story appears to be confirmed by his manuscript notes. If not in August 1563, no doubt by May 1564, he did indeed start making notes (already using his new radius) reporting on the differences between his observations and the ephemerides of both Johannes Stadius (1556) and Giovanni Battista Carello (Reference Carello1557).

In searching for Tycho's first motivations towards astronomy it is worth looking closely at the first book in question, Stadius’ Ephemerides novae et exactae, which was introduced by an important letter written by the Dutch mathematician Gemma Frisius (Stadius Reference Stadius1556, a_r-aii_v; Thorndike Reference Thorndike1956b, 13–15; Hallyn Reference Hallyn1998 and Reference Hallyn2008, 190–212). Writing in the last year of his life, Frisius vigorously defends Copernicanism and urges Stadius to ignore accusations of falsely believing that the earth moves and the sun is at rest; he exhorts him to follow the Prutenic Tables and his own observations, since Copernicus’ system better explains the phenomena. Stadius in the book's dedication to Philip II makes a similar argument, emphasizing that the theory of celestial motion needed correction and existing ephemerides failed to agree with reality. He claims to have based his own ephemerides upon the Prutenic Tables, testing them for two years against his observations and those of other astronomers. We may justly suppose that when the young Tycho compared his own observations with the ephemerides of Stadius and read about those of Gemma Frisius described in his De radio astronomico et geometrico (Reference Frisius1545), he identified with Stadius and began harboring similar observational ambitions.Footnote ⁵ But we may likewise presume that the Dane shared not only Frisius’ and Stadius’ observational program in the framework of Copernicus’ reforms, but also their astrological approach and objectives. In the dedication to Philip II Stadius had asserted that the planets had control over the weather and political changes, some of which he foretold. He also attached an interpretation of the horoscope of the Prince of Orange. Yet Stadius was not a vulgar astrologer; he was a characteristic sixteenth-century reformer of astrology, as revealed in his Tabulae Bergenses (Stadius Reference Stadius1560). This book promised a compendium of Copernicus’ De revolutionibus and the Prutenic Tables, provided an erudite history of astronomy, practical astronomical know-how (easy ways to calculate planetary positions), and astrological foreknowledge related to fixed stars and planets.

As Tycho admitted in the quoted autobiographical notes, astrology was and remained dear to him. His early belief and practice of judicial astrology is also documented by some of his later letters and notes. In an often cited letter of 1588 to Caspar Peucer explaining his world system he recalled the nativity of Peucer that he had produced many years earlier in Leipzig (TBOO 7, 137–8). “Discovering” the horoscope in his old horoscope book, he extensively quotes from it, even while admitting the original reading had been done purely out of juvenile curiosity. Later – he claimed – having noticed the discrepancies between different astronomical tables, his attention would eventually turn towards the emendation of planetary movements. Peucer's horoscope had foretold misfortune for religious reasons, long exile or imprisonment with liberation close to the age of 60. This was exactly what happened to the Wittenberg physician, who was imprisoned in 1574 and released only in 1586 at the age of 61. Tycho claimed he did not quote the horoscope to ascribe too much to the force of the stars, but only to let Peucer know what he had once written down, in a period when he had been more zealously dedicated to such things. Less fortunate was the young Tycho's horoscope concerning the death of the aging arch-enemy Suleiman I. Among his notes he later admitted that in 1566, shortly after his arrival in Rostock, he had posted some “heroic” Latin poems at the university, foretelling Suleiman's death as a consequence of the lunar eclipse of 28 October. Unfortunately, it turned out that the sultan had already died in September. When a Rostock theology professor, a devotee of astronomy but less inclined towards astrology heard and read the poems, he poked fun at the augury (TBOO 1, 135; Dreyer Reference Dreyer1890, 26). In the same period Tycho was also interested in weather prognostications: he allegedly correctly foretold wet weather from a lunar eclipse, and from the last days of 1564 attempted to predict the weather of 1565, each day signaling a month of the following year (Dreyer Reference Dreyer1890, 21).

Tycho's interest in natural and judicial astrology continued throughout his life. Later, however, he would emphasize his detachment, in particular that he pursued predictive astrology only as it was a requirement of his court service (TBOO 7, 116–9; Thoren Reference Thoren1990, 120–2, 141–2; Oestmann Reference Oestmann and Christianson2002). However, in his autobiography he would not go into details. In fact, the years when traditional astrology probably had the strongest grip on him are elegantly passed over; it is no coincidence that his early astronomical notes stop subsequent to his departure from Leipzig in May 1565. The next four years of intense travelling between Wittenberg, Rostock, Basel, Augsburg, and Denmark are glossed over in only a few lines. It is clear these years were dedicated mostly to alchemy and astrology and significant to Tycho's intellectual maturation and development as a Paracelsian thinker. Yet except for the period spent in Augsburg they had little to do with the persona of the observational astronomer Tycho would later cast for himself (Thoren Reference Thoren1990, 22–36).Footnote ⁶

The diverse influences Tycho encountered in this period are also reflected in the different contacts he made. Among his new acquaintances there were mathematicians like Heinrich Brucaeus, a student of Ramus and a fierce enemy of astrology, and also astronomer–astrologers like Cyprian Leowitz, who showed Tycho his manuscript ephemerides, tables of directions, and other observations similarly based both on the Alfonsine and the Prutenic Tables (TBOO 3, 220–1). During this period Tycho as an instrument maker was introduced by the erudite Greek scholar Hiernymus Wolf to Petrus Ramus himself, who demanded from him an astronomy without hypotheses (TBOO 6, 88–9; TBOO 2, 346–7; Gassendi Reference Gassendi1654, 16–7). Wolf became one of his contacts and clients, having significant interest in problems of astrology. He was strongly influenced by the dire auguries Tycho had cast for him in 1569 in Augsburg, which corrected Wolf's horoscope made by Leowitz, adapting it better to past and future happenings.Footnote ⁷

Entering the public domain

The conventional caesura in Tycho's self-narration and biographies was the appearance of the shiny star of 1572, which most contemporaries considered a wonder sign, and many felt confirmed their apocalyptic views. Tycho described the event and its great significance for him:

It was thus the supernova of 1572 that made him turn his full attention to astronomy for a long while. More importantly, it was the new star that prompted him to decide to enter the public domain, making him a pioneer in turning scientific practice into published result as an aristocrat. It was one thing to be a noble practitioner and pursue astrology in private, quite another to go into print and take up the public challenge. Tycho himself would emphasize that by going into print, he ran counter to prejudices concerning the proper role and place of the nobility in society.Footnote ⁸ However, he was certainly not the only exception (just think of his friend the governor of Holstein Henrich Rantzau), and the story of his long hesitation, which he had already lyrically presented in his Elegy to Urania in 1572, seems more a literary convention than a reflection of social reality. Most probably he needed neither the encouragement of his Copenhagen friend Iohannes Pratensis (Jean de Près) nor the persuasion of others (TBOO 1, 6–11; TBOO 3, 93–6).Footnote ⁹ Tycho's narrative points out that when the star flared up in November, 1572, he was in the midst of writing an astrological-meteorological calendar, and his initial thought was to simply append his new observations to it. He interrupted his astrological work-in-progress and wrote the treatise on the star, and then first approached people in Copenhagen with both the calendar and the attached treatise. If the dating of December is valid, it is clear that by that time he had already written the erudite preface to the calendar, which was an introduction to astrometeorology “proposed for those who are fond of both astrologies.” If this story is true, it is curious why and for whom Tycho prepared the almanac and the erudite introduction, and whether he was not considering publishing or circulating them quite apart from the matter of the appearance of the nova. As the new year began, the publication of the almanac was pressing more and more, in contrast to the treatise on the nova, given that initially no one around Tycho had even noticed the new star. In the book eventually entitled Concerning the New and Never Seen Star in the Memory of Times he only retained the “contemplatio mathematica” (the treatise on the star), the erudite introduction to calendar making, and his astronomical-astrological analysis of the lunar eclipse of December 1573, while he dropped the idea of also publishing the “diary” (TBOO 1, 1–72). As the title lines of the publication declared, the almanac “made with unique diligence” was left unpublished because of typographical difficulties and lack of time.Footnote ¹⁰ This of course patently conflicts with Pratensis’ reference to Tycho's independent decision in the preface (TBOO 1, 7).

If we suppose Tycho originally pondered another kind of book (perhaps for manuscript circulation), for example an almanac for 1573 with tables of the risings and settings of the sun, moon and planets, their various configurations, the horoscope for each month, and predicted weather for each day (TBOO 1, 76–130), then his debut as an astronomer would have been of quite a different nature. As Pratensis stressed, the almanac was a great contribution to astrology, correcting several errors of ordinary astrologers and less certain questions of the art (TBOO 1, 6). Tycho, in fact, had by that time developed an individual stance towards astrology, placing great emphasis on lunar phases (octads), applying the genethliacal technique to meteorological astrology, and using eight astrological houses instead of twelve (probably because of the influence of the moon).Footnote ¹¹ Despite these and many other novelties, had he also published the calendar, it would have been on record in a sea of other almanacs, making the figure of the astrologer cast a dominant shadow on his emerging reputation.

The calendar was left in manuscript, but its introductory essay was published right after the tract on the nova. This essay, in fact, presented the cosmological credo of the author in characteristically Wittenberg terms (TBOO 1, 35–44). The “celestial workshop of the universe” testified to divine wisdom more than anything else. It was created for man's good, God placing him in the center and letting him contemplate, as in a mirror, its nature and constitution. Its size, form, lightness, perpetual and predestined revolution revealed that the superior part of the world far supersedes the inferior part. Nevertheless, only a few people investigate the heavens, therefore this science is disdained by the unlearned, and even ridiculed by some erudite men. Although the opinion of unlearned folk matters little, unfortunately even the few who engage in astronomy abuse the art. Tycho did not want to judge those excellent men who research the revolution of the orbs, but those who dedicate their study to the effects and influence of the stars are mostly unworthy of the job: they are not ashamed to offer their work for sale. On the one hand, practitioners of judicial astrology had perverted the art of horoscopes, which depends on the correct position of the stars, following vain authority, “which has as little place in mathematics as in other human inquiries,” instead of their own experience (TBOO 1, 36). On the other hand, those who consider meteorological influences had prostituted the art so much that even the ignorant folk can see how vain and worthless annual prognostications are. Tycho ended his criticism with a reference to a work he had allegedly written, Against Astrologers for Astrology. The essay thus presented its author as a critical astrological reformer fully conscious of the fallacies of the art. Moreover, at the end of the text he promised to put astrology on better astronomical foundations, and base his later weather prognostications on the cumulative experience of confronting meteorological and stellar observations. This was, however, nothing new in the latter half of the sixteenth century (Thorndike Reference Thorndike1956a; Thorndike Reference Thorndike1956b, 99–144; Vanden Broecke Reference Vanden Broecke2003).

The decision to omit the almanac and place the treatise on the nova in the center completely changed the balance of the book. Although the essay on the new star followed more or less the structure of traditional Latin cometary treatises, it was an emphatically “mathematical” presentation of the subject leading up to a number of daring conclusions. Most importantly, it is remembered for its powerful attack against the Aristotelian cosmos, its precise data measuring the star's position – revealed as being far above the sphere of the moon (Thorndike Reference Thorndike1956b, 67–98; Hellman Reference Hellman1960; Methuen Reference Methuen1997; Weichenhan Reference Weichenhan2004, 591–608; Gingerich Reference Gingerich and Turatto2005). In the final version the book was principally about astronomical knowledge production, underlining Tycho's practical skill in drawing valid natural philosophical conclusions from observed heavenly phenomena. While astrology remained an integral part of the book, it was tamed and apologetic, and in the prognostications – as befitting a wise astrologer – the author refrained from anything but generalities, veiling his augury about the death of King Frederik II (as foretold by the lunar eclipse) in a densely woven fabric of allegory.Footnote ¹² Even the predictions based on the appearance of the nova – great political changes, human and natural disasters – were presented in an apologetic framework. Tycho confessed he knew nothing concerning the star's generation and the reasons for its appearance (TBOO 1, 19). Nevertheless, out of the 36 pages the last 9 were dedicated to astrological interpretation, which then finished with a new apology. The author acknowledges more precise information could also be foretold within the framework of this kind of vulgar astrology, but prefers not to present astrology's better founded and more secret sources known only to a few people (and hated by several), since it would be a crime to prostitute its mystery (TBOO 1, 34).

The astrologer's incertitude

If Tycho required any reassurance to publish his book, he must have received it while reading the first German publications on the new star, providing poorly made observational results and false theoretical conclusions.Footnote ¹³ As it turned out, the public response to the nova, numbering several dozens of tracts and pamphlets, was far greater than anyone could possibly have imagined at the beginning of 1573 (Thorndike Reference Thorndike1956b, 67–98; Hellman Reference Hellman1944, 113–117; Hellman Reference Hellman, Koyré, Cohen and Taton1964; Weichenhan Reference Weichenhan2004, 467–591). Surely, this was an enormous stimulus for further research, and there was also much to learn from contemporaries, many lessons to draw and many more mistakes to avoid. A richly documented example is a 176-page book entitled Dialexis de novae et prius incognitae stellae written by the Bohemian botanist, doctor and astronomer Tadeáš Hájek (Hagecius Reference Hagecius1574; Hellman Reference Hellman1944, 184–208; Fenton Reference Fenton1998, 134–5; Drábek Reference Drábek2000; Smolka Reference Smolka and Christianson2002, Reference Smolka and Enderle-Burcel2008). It merits a short excursus, since Hájek and Tycho (see below) would mutually influence each other significantly in their publication strategies.

The Bohemian astronomer confesses he was drawn to writing on the subject due to the apparent divergence of opinions over the nova and a desire to speculate on the future given he was living in a time of turmoil (Hagecius Reference Hagecius1574, 5–6). Unlike Tycho's work, Hájek's writing was thus referential and agonistic. He repeatedly refers to and critically comments on the work of other astronomers, even attaching the writings of some to his treatise. Both these attachments and his pointed commentary taken together were intended to persuasively impress readers of his credibility and authority, offering a masterful survey of the whole set of issues and questions at hand.

The text opens with Hájek pointing out the inaccuracies of his Spanish astronomer friend Jerónimo Muñoz, and then refutes the opinions of two lesser known Venetian astronomers Annibale Raimondo and Cornelio Frangipane. The tone is unmistakably harsh and offensive. For Hájek, the two Italians were not only bad astronomers but also (partly as a consequence) bad and superstitious astrologers (ibid., 31). Their opinions were not only false but practically unchristian. In the main, Hájek's argument, written independently of Tycho, was the same: the nova appeared in the sphere of the stars, and hence was evidence against Aristotle's vision of celestial incorruptibility. The theoretical claims against Aristotle were then supported by astronomical proofs, including Hájek's measurements of the distance of the nova, which were compared to the results of three other astronomers (ibid., 64–5). As in Tycho's case, the great distance of the nova from earth was clearly the central thrust of his thesis; Hájek also attempted to explain the science of parallax measurements and the technique of modern astronomical observations. It is in the last three chapters of the essay that he turns to the traditional astrological meaning of the new star and its religious implications, self-referentially asserting that the book would appear unfinished without astrological prognostication (ibid., 98). Hájek foresaw apart from social unrest and changes in political regimes a successful but contested spread of the “one and pure doctrine” (i.e. Lutheranism) (ibid., 102–3).

Tycho could draw both positive and negative lessons from Hájek's book, which he later judged the best among contemporary works (TBOO 4, 261). First, he could be reassured by his conclusions on Aristotelianism and observational precision.Footnote ¹⁴ More importantly, it was Hájek's discursive rhetorical technique that constituted a positive example for the Dane, in the presentation of astronomical knowledge and asserting his pre-eminent authority by refuting, criticizing, or supportively presenting the work of other astronomers. While Tycho referred to no other astronomers in his 1573 treatise, he later adopted and perfected Hájek's referential and competitive method of composition in both of his main works, the Concerning Recent Phenomena in the Ethereal World (Brahe Reference Brahe1588) and the Introduction to the New Astronomy (Brahe Reference Brahe1602). However, there were at least two fundamental negative lessons as well. One concerned the way referential scientific discourse needed to be used: with a measure of politeness and within the rules of civility. This was not the method Hájek pursued in the Dialexis. His harsh attack on Catholic astrologers led to a variety of ideological controversies which lasted for more than a decade, all of which was totally alien to Tycho's irenic tone and conscious avoidance of religious controversies.Footnote ¹⁵ He not only was opposed to Hájek's controversial publications (TBOO 7, 74 and 204), but later overtly condemned the calendar controversy as being irrelevant for religion and used to merely stir up social unrest.Footnote ¹⁶ The other lesson Tycho could draw from his contemporaries’ publications was a sharpened awareness of the difficulties of treating astrology within the framework of a referential scientific discourse, since the outcome of prognostications was so difficult to verify. Entering the arena of astrological prediction, increasingly invaded by popular astrologers, must have appeared to make less and less sense (Dixon Reference Dixon1999).

It is of course impossible to identity what factors made Tycho draw these conclusions, but certainly his rhetorical strategies were now going to change. To be sure, after the appearance of the Concerning the New and Never Seen Star the problem of astrology's rightful place among scientific activities (and his own self-image) would continue to trouble him. In 1574 he accepted the royal commission to hold a special lecture series at the University of Copenhagen, and in his first public oration (which remained unpublished at the time) he ventured to systematically refute the major arguments of philosophers and theologians against astrology (TBOO 1, 145–170; Thoren Reference Thoren1990, 80–85; Christianson Reference Christianson2000, 17–18). In general, this history and defense of astrology – with its emphasis on Copernicus’ achievements (underlining the solution of an equantless model), the Paracelsian correspondence between man as microcosm and the universe as macrocosm, and man's free will as against astrological determinism – was not very original but nonetheless well suited the Philippist and Paracelsian milieu of the Copenhagen court and university (Lockhart Reference Lockhart2004, 75–83; Christianson Reference Christianson1979, 114).Footnote ¹⁷ Moreover, it was elegantly written and sufficiently compelling (as Tycho noted after the lecture) to make some critical members of the audience believe astrology practiced intra suos terminos meant no risk to theology or philosophy, and that as an a posteriori science it had a valid place among other sciences (TBOO 1, 170–3). Once again, the problem with astrology, Tycho emphasized, was the activity of ignorant and malevolent abusers of the art and the resulting associations with superstitious forms of augury (TBOO 1, 162; cf. Hemmingsen Reference Hemmingsen1575). Not even the strident Pico della Mirandola had been moved to write against astrology because of unbelief in the stars’ influence, but rather by his irritation over the superstition and falsity of pseudo-astrologers. In this concern, no one devoted to the more secret and genuine form of astrology would disagree with Pico (TBOO 1, 168).Footnote ¹⁸

Just how much astrology was in need of defense is best illustrated by the continuous flow of publications for and against it. If Tycho picked this subject, it was also because it had a receptive audience, and there were important people to be convinced or mollified in his environment. In fact, during the table-conversation which followed his inaugural lecture some influential members of the audience still voiced their doubts. While Tycho's friend, the French ambassador Charles Dançey, articulated his worry that astrology (which he had practiced as a young man) was against evangelical teaching, the chief theologian of the university (and thus royal censor) Niels Hemmingsen – as always preoccupied about predestination – confirmed astrology must not tie the hands of man or God (TBOO 1, 171–2).Footnote ¹⁹

Nonetheless, it would be difficult to judge the ratio of foes to believers of astrology. The spectrum was sweepingly wide and the dividing lines blurred between the very few who denied the influence of the stars outright, to those who questioned certain methods or branches of astrological foreknowledge to the naively unreflective advocates of all kinds of astrology. An excellent example would be the Transylvanian Thomas Jordanus, doctor of Brno. While he would not deny the moon could influence human health nor that great conjunctions could cause horrible pestilence, he was unwilling to explain the epidemics that started in one of the baths of Brno as the work of a comet (Jordanus Reference Jordanus1580).Footnote ²⁰ In any case, believers in astrology could be deeply offended by accusations of superstition, but could easily project the same fault on others. Both critics and defenders of astrology were defensive, seeing the others as the majority. Gervasius Marstaller (Reference Marstaller1549, 4) complained in Paris that there was hardly anyone who worked on the restoration of astrology's ancient dignity. Nine years later, Hieronymus Wolf (Reference Wolf1558) claimed astrology was the object of much hatred and envy, because it had been abused and prostituted by unscrupulous astrologers. Nicolaus Wincklerus (Reference Wincklerus1580, A2_v) lamented that astrology was so much hampered in his town Schwäbisch Hall that local people deemed it praiseworthy to publicly castigate it and denounce as illicit. On the other hand, when Andreas Dudith reproved cometary astrology in 1578, he affirmed this was against the common opinion (Erastus et al. Reference Erastus, Dudithius, Squarcialupus and Grynaeus1580). This was probably true, which is also indicated by the continuous spread of astrological publications well into the late seventeenth century. To be sure, very few serious astronomers in the sixteenth century neglected (or denied) the basic tenets of Ptolemaic astrology. In particular, with the exception of Michael Maestlin's published treatise on the new star (1574), hardly any publication disregarded astrology among the reactions to the supernova or the comet of 1577, although probably few astronomers (or mathematicians, as they were commonly called) engaged with astrology unreflectively any longer.Footnote ²¹ But there were also several men of prestige who like Dançey or Hemmingsen had serious doubts. This circle included a number of distinguished intellectuals such as Theodor Zwinger (Reference Zwinger1604, 1273–5) and Joseph Justus Scaliger, several of whom were also anti-Paracelsians, and most importantly Thomas Erastus who was personally attacked by Tycho in his public lecture and elsewhere (TBOO 1, 166–7).Footnote ²² Finally, there were prestigious members of the Catholic Church, like Antonio Possevino (Reference Possevino1603, 278–84), who denounced astrology, while significantly Sixtus V published the second papal bull against astrology in 1586 (Thorndike Reference Thorndike1956b, 145–178; Verardi Reference Verardi2009).

The case of the Augsburg humanist Hieronymus Wolf illuminates the extraordinary ambivalence towards astrological lore and practice in Tycho's environment. This self-absorbed, hypochondriac humanist superstitiously believed in the influence of stars when it concerned his own person, but was apparently seriously bothered by the divergent opinion of individual astrologers and the many difficulties that concerned horoscope making (Thorndike Reference Thorndike1956b, 112–4; Allen Reference Allen1941, 75–8; cf. Wolf Reference Wolf and Zäh1998, 16–23, Algazi Reference Algazi and Dekker2002, Keil and Zäh Reference Keil and Zäh2004). He voiced his doubts in a dialogue as early as 1558 and came back to them in 1575 in a letter to Tycho demanding his Danish friend respond to a list of controversial points concerning astronomy and astrology (TBOO 7, 15–8; cf. Wolf Reference Wolf1558). These ranged from problems of the spheres and the motion of the planets to the difficulties explaining the horoscopes of twins. There is no evidence Tycho replied, but some of his answers (like the Ciceronian problem of twins) were already laid down in his unpublished Copenhagen oration. There is no sign of communication between them until three years later, when the old friend indignantly complained that people returning from the Isle of Hven brought no letter for him. Wolf sarcastically commented that it was surely not due to Tycho's disdain of his ignoble origin or poverty. The Dane must have believed him dead, as he had once foretold the danger of death for him when they had been discussing his horoscope in Augsburg. There Tycho had wanted to share with him some parts of his hidden astrological treasures (TBOO 7, 47–48).

Tycho's growing reservation towards public astrological pronouncements

Tycho could not remain unaffected by the incertitude that surrounded astrology, the failures of prognostications (including his own), the theoretical problems of astrology/astronomy given voice by Pico and others (Westman Reference Westman2011, 245–250), and attacks on astrology which reached a new height after the appearance of the comet of 1577. Moreover, he certainly must have been impressed by the diversity of astrological prognostications (which of course critics of astrology happily pointed out) in the countless publications inspired by the nova and the comet (e.g. Erastus et al. Reference Erastus, Dudithius, Squarcialupus and Grynaeus1580, 40–44). Nevertheless, while incertitude did not shake Tycho from his belief in astrology, it did lead him to modify some of his conclusions, and most importantly his public attitude towards astrological ideas.

This change of attitude is first noticeable in the fact that Tycho's initial reaction to the comet of 1577 was an unpublished short tract written in German (TBOO 4, 380–96; Christianson Reference Christianson1979). It was clearly not meant for the Republic of Letters, but most probably aimed rather to satisfy his royal patron King Frederik II and his worthy courtiers. By the time of the comet's appearance Tycho had already been made Lord of Uraniborg and beneficiary of a royal pension. Although he had no explicit contractual obligations, it must have been evident that Frederik's most generous gestures had to be duly repaid. Tycho's service was partly astrological consultancy, offering privileged access. Obviously the king would be in a position to discourage the publication of astrology's better founded and more secret sources, to which Tycho alluded in 1573, and rather have them whispered in his ear. Nevertheless, what remained for posterity in manuscript form is quite substantial. The 30-page German treatise Tycho prepared to share on the occasion of the comet's appearance was one gesture to show his gratitude, just like the 73-page horoscope for the birth of Prince Christian which he had written the summer before (TBOO 1, 183–208; cf. Thoren Reference Thoren1990, 120–1).

Even if written only for some select readers, the Vonn der Cometten Uhrsprung had a very precise social context (Christianson Reference Christianson1979; Thoren Reference Thoren1990, 128–132). John Roberts Christianson argues that Tycho could not just disregard the emerging respect for a talented astronomer Jørgen Dybvad, especially since Dybvad noticed the comet in the company of the king two days earlier than he had and was ready with his analysis within five weeks (Dibvadius Reference Dibvadius1578). Dybvad was clearly a dangerous competitor because he was similarly enthusiastic about Copernicus and like Tycho believed the new star of 1572 was a celestial phenomenon. His treatise was well received at court, and he soon managed to land the university chair of mathematics in Copenhagen and a royal order granting him the monopoly on the publication of almanacs.

Tycho's German treatise on the comet was a balanced, masterly treatment of the subject at hand, structured in the same way as most cometary treatises. Since parallax measurements and calculations showed the comet was far above the moon, Tycho's attack on Aristotle was even more straightforward than his earlier one, rejecting also the claim of the existence of four elements in favor of three. While he gave a plausible description of the comet's material, color, and diameter, and rightly supposed it rotated around the sun, he refused to present any conjectures about its origin. This strategy of pious ignorance served to articulate the wondrous nature of this “pseudoplanet.”Footnote ²³ He laid great emphasis on the correct observation of the comet's duration, position, course, tail (which gave him new occasion to reject Aristotle), size, and distance from the earth – which apparently were not priorities for Dybvad. Yet, the king was less interested in such astronomical detail than in Tycho's interpretation of the fearsome omen provided in the final ten pages of the essay. Although speaking to a small public (just like in Prince Christian's horoscope), Tycho was again eager to present himself as a cautious astrological reformer. As an introduction he criticizes astrologers for attributing significance to planetary configurations at the moment of the comet's birth since the influence of unnatural wonder signs should not be linked to the common work of the planets and stars. While he confirms man cannot completely understand these heavenly miracles, he also asserts there is sufficient space for interpretation made without superstition if one relies on the experience of the ancients. Like most of his contemporaries, Tycho foresaw disunity, bloodshed, wars, pestilential and poisonous sicknesses, great alterations, and reformation of both spiritual and secular regimes.

Tycho would not venture any more, apart from one case mentioned at the end of the paper, into astrological prognostication in public writings under his name. One may argue that the social-political meaning of the comet was the last thing Tycho was concerned about. The comet of 1577, crossing the orbs of planets and apparently revolving around the sun far away from the earth, raised far greater questions that spurred Tycho to study cosmological problems intensively and later perform prolonged observational campaigns of the Moon and Mars (Thoren Reference Thoren1990; Gingerich and Westman Reference Gingerich and Westman1988; Gingerich and Voelkel Reference Gingerich and Voelkel1998). The sketches he made during the observation of the comet already show his interest in the relation of the comet to the system of planets (Christianson Reference Christianson1979, 122–5; Westman Reference Westman1975b; Gingerich and Westman Reference Gingerich and Westman1988).

However, none of this necessarily means that astrology lost its importance for Tycho. His strenuous observation of the fixed stars, the planets, the moon, and the sun could be interpreted as an attempt to prepare more correct tables, the results of which would “serve as a basis for the calculation of ephemerides for the coming years” – as he noted in his autobiography in 1598 (Brahe Reference Brahe, Raeder and Strömgren1946, 115).Footnote ²⁴ Moreover, his attempt to keep the universe small with the design of his world system, forbidding the fixed stars from remaining at the incredible distance found in the Copernican scheme,Footnote ²⁵ might have been as much motivated by astrological considerations as his resistance to the idea of a rotating Earth, which would not “peacefully take in the active influences of the skies.”Footnote ²⁶ His insistence on a particular arrangement of the planets appears thus closely linked to his Paracelsian universe where the terrestrial reflected the heavenly, the two remaining physically discontinuous.

Nevertheless, astrological prognostication clearly lost priority in Tycho's scientific activity. If we accept the notion that “historical and social interests, not systems of logic, determine what shall count as knowledge” (Martines Reference Martines1979, 201), we cannot disregard the ambiguous status of astrology in this context. I contend Tycho's change of scientific program and publication strategy were prompted by the recognition that astrology, invaded by amateurs, had lapsed further and further into a slippery field in which no spectacular advances could be made. In this context rival astrologers’ conjectures remained badly supported by observational evidence, and thus could not be convincingly outdone. This, in turn, resulted in a change of rhetoric, and heightened attention to drawing correct mathematical conclusions through precise observations made by using refined highly tuned expensive instruments.

Tycho's new attitude towards public discourse on astrology is further illustrated by his reaction to the less spectacular comet of 1585. The publication produced for the occasion weirdly resembled the original publication plan dealing with the supernova of 1572: a Latin cometary tract included in an astrological and meteorological calendar for the following year. However, the book now came out under the name of Tycho's assistant Elias Olsen Morsing (Reference Morsing1586), who had since 1583 been responsible for keeping day-by-day meteorological notes (TBOO 9, 5–146; cf. Christianson Reference Christianson2000, 323–5). Since Tycho had been already preparing for his major opus on all recent celestial phenomena (among which this little visible comet had only minor importance) the author of the short treatise claimed he had decided not to treat this complex phenomenon in detail (TBOO 4, 401). As a consequence, most of the tract was pure astrology, but now the apologetic statements were even more pointed; while the observational data are infallible, prognostications are only probable. By asserting the old thesis that comets about the same size as the earth (that is, great enough to have an extraordinary effect) are not placed in the sky only for spectacle, Tycho also explicitly refers briefly to recent anti-astrological publications – most probably from Thomas Erastus, Andreas Dudith, and Marcello Squarcialupi – who denied cometary influences altogether (TBOO 4, 402). Although he belittles these works (and particularly hates the anti-Paracelsian Erastus), he could not have remained uninfluenced by the erudite arguments of Dudith and Squarcialupi demanding (with a similar anti-Aristotelian attitude as his) that scientific research be limited to the investigation and observation of proximate causes.

Tadeáš Hájek received a copy of the Morsing-Tycho calendar soon after it appeared in Frankfurt. The Bohemian astronomer, who had ardently defended cometary astrology against impious Epicureans like Erastus and Dudith (Hagecius Reference Hagecius1580), now claimed he recognized Tycho's voice:

Tycho's apologetic stance becomes even more understandable if we look at the letter of another friend, the Belgian mathematician Henricus Brucaeus. Brucaeus felt shocked when he learned about Tycho's intention to publish the calendar of one of his disciples. He claimed Tycho should not allow this kind of vulgar writing to be printed by his press; that foreseeing weather changes for a year makes one ridiculous in front of everyone. Thanks to the failures of these weather forecasts, these prognostications are taken as trifles or lies. Brucaeus was all the more surprised since he recalled a private conversation once with Tycho about astrology and remembered Tycho did not think more of astrological prophecies than was their due (TBOO 7, 91; cf. p. 100).

Maturing as an astronomer, Tycho also had to realize that some problems in natural astrology were difficult to deny. One such problem concerned the different weather conditions across Europe despite unitary planetary influences, a point already underscored by Thomas Erastus (Gunnoe Reference Gunnoe and von Greyerz2010, 91). Tycho now asserted that distances between the Earth and the planets were so great that with reference to their influence on the climate it would matter little whether one stood on Hven or in Prague. He closed his review of Cornelius Gemma's and Hájek's observations by warning the devotees of meteorological prognostications

Tycho was apparently not uninfluenced by criticism and apparent difficulties. Nevertheless, Elias Olsen Morsing's book was not the last astrological work that would appear from his press. In 1591, at King Frederik's request, Tycho's disciple Peder Jacobsen Flemløs published another book on astrometeorology, this time written in Danish. Although astrological information was virtually absent, Tycho wrote an apologetic preface to the book under Flemløs’ name (Flemløs Reference Flemløs1591).Footnote ²⁸ He again stated that astrology was such a sublime art that many of its parts remain above human comprehension and that no one had yet managed to render it into a rightful science. But even among partisans none really studied it diligently enough, for astrology ought to be based on a good understanding of astronomy and its foundations in the arts of geometry and arithmetic. Astrology thus needs more than the knowledge of astrological signs, and surely common people, such as writers of almanacs, would never have a proper understanding of it.

While in the public domain Tycho hid behind his assistants, he also revealed increased alertness in private when it came to predictive astrology. At the end of 1587, the Duke of Mecklenburg asked through a friend for his opinion about two contrary prognostications concerning the much-feared year of 1588 (Dixon Reference Dixon1999). Tycho's German response was obviously not intended for later publication. But even in this private letter he was strongly apologetic: he neither happily engaged in astrology nor cared to read contemporary prognostications, because they have little reliability and are full of doubts, being based on poor and diverse astronomical fundamentals. However, if the Duke wanted to know his opinion of the following year (which contrary to vulgar pamphleteers appeared to him a normal year), he was ready to have a copy made of the almanac he had prepared for the Danish king on royal order (TBOO 7, 116–9).

The new scientific discourse and Tycho's criticism of astrology

The two works immediately following the comets of 1577 and 1580 were certainly not meant to be Tycho's final statement. He generally recognized the many thorny astronomical, natural philosophical questions raised by the comet of 1577, and diligently gave himself over to resolving them; from 1578 he began preparing a major Latin monograph.Footnote ²⁹ The “Tychonic world system,” which brought him further fame, was one of the outcomes of his considerations of the mysteries of the comet's course in the sky. In fact, Tycho included the explanation of his planetary system integrally in his magnum opus Concerning Recent Phenomena.Footnote ³⁰

Tycho's book on the comet eventually preceded the new monograph on the nova, the sun, and the moon (Introduction to the New Astronomy), which appeared posthumously in 1602. Concerning Recent Phenomena (1588) was a late but fully matured response to the astronomical challenges of recent celestial phenomena; its 465 neatly printed pages could in no way be compared to the more than one-hundred treatises and pamphlets that appeared in 1578 and shortly thereafter.Footnote ³¹ There is no distortion of the past in Christianson's argument (2000, 105) that the book was a real breakthrough: “Tycho Brahe produced a paradigm of the modern scientific monograph: a thorough, systematic treatment of a single subject, written for a scholarly audience.” Without a doubt, Tycho's primacy in the community of astronomers was revealed not only by the exceptional amount of observational data concerning the comet and the stars, or new theoretical insights and cosmology aiming to surpass both the Aristotelian-Ptolemaic and the Copernican systems, but also through a most detailed review of the works of contemporaries. Tycho, unlike say Copernicus, continuously mentioned the results of fellow-astronomers both in the text and in a systematic review of all major works in the last chapter, which consumed more than half of the book (TBOO 4, 180–377). In this chapter, Tycho repeatedly points out the precision of his observations and validity of his conjectures, distinguishing what he envisages as right and wrong in the work of others. Significantly, he emphasizes his judgment by reviewing separately those astronomers who correctly judged the comet to be above the moon, and those who still believed the comet was a sublunary phenomenon. This thematic division had a lasting effect; the scientific discourse of late sixteenth-century astronomy regarding comets would often follow these lines (such as Hellman Reference Hellman1944).

If there were serious competitors to Tycho's grandiose project, Tadeáš Hájek was certainly one of them; he had been working on the enlargement of his treatise on the supernova for a similarly long time. It was not only Tycho who highly appreciated Hájek's Dialexis, but also the wealthy Breslau based humanist Andreas Dudith, who offered himself as patron. However, just like Tycho, Dudith was deeply unenthusiastic about the confessional undertones of Hájek's work, insisting he remove the ideological content and make the study a more elaborate, purely mathematical work.Footnote ³² It is patently clear that for Dudith “mathematical work” by definition excluded all kinds of astrological prognostication. By 1582 Hájek did indeed rewrite the book, embracing considerations about the comets of 1577 and 1580. In addition to observational fallacies, he corrected his mathematical presentation of parallax measurements, taking into account both the criticism of Tycho and Paulus Wittich, and the results of Thomas Digges (TBOO 7, 71–2). When in 1583 he wanted to incorporate Tycho's astronomical observations into the work, the Danish astronomer refused, claiming he had already been working on a similar project on recent celestial phenomena (ibid., 73). Two years later Hájek reported he had considerably augmented his work, adding a synopsis of all other tracts on the subject which seemed consonant with his views. He now offered the book to Tycho's press and alluded to the possibility of a joint publication (ibid., 104), but generously allowed his colleague to use excerpts from it for his own work (TBOO 7, 99). At the same time Andreas Dudith offered to finance the printing again, demanding Hájek send him a draft of the new manuscript so he the amateur and his expert Breslau friend, Paulus Wittich, could read and review it. Following their editorial opinion was no condition of patronage from Dudith, so Hájek was assured that he was free to decide on the final version.Footnote ³³ Nevertheless, the Bohemian astronomer did not deliver his manuscript to Dudith. He might not have wanted Wittich or Dudith to criticize his book again and preferred to let Tycho decide the fate of his work. His earlier quarrel with Dudith over astrological prognostications may also have remained an unpleasant memory even if he now appeared ready to accept some points of anti-astrological rhetoric.Footnote ³⁴ In fact, in the new 1584 edition of his Aphorismi Metoposcopici (the science of predicting the future by reading one's forehead), Hájek declared that he had been losing interest in public prophesy and blamed the proliferation of false prophets.Footnote ³⁵ If Hájek preferred to be associated with Tycho in the publication of his new Dialexis, it was probably because Tycho had already proved to be his clear superior in astronomical matters.Footnote ³⁶

Hájek's (unrealized) publication project and concept of revising the works of other astronomers certainly was not without influence on Tycho, who apparently also felt an affinity for Dudith's advice to keep the treatment of astronomical phenomena purely mathematical. In any case, his magnum opus Concerning Recent Phenomena was a single-minded treatment of observations and conjectures about them. If this monograph was paradigmatic (in the Kuhnian sense) in the interpretation of celestial phenomena, it was to a large extent due also to the new discursive techniques that left absolutely no space for astrology, apart from short negative comments regarding the astrological parts of contemporary treatises. As Tycho repeatedly emphasized, his book was about astronomy and not astrology. The first negative comment on astrology alluded to the cometary book of Michael Maestlin, Kepler's master (TBOO 4, 237–8). Tycho declared he would not give his opinion about the tenth chapter of Maestlin's work which concerned the significance of the comet. He disregards astrology not because this science is useless or uncertain – given that its limits are respected and it is not abused superstitiously – as claimed by many erudite men and even some mathematicians. For Tycho, astrology is firm enough, even though one can hardly find experienced astrologers who would study it with due diligence and observance of its limits. However, he also acknowledges that astrological prognostication in regards to new miraculous phenomena (like the nova and the comets) is even less reliable than in other cases:

Later in the work his comments on the astrological views of others gradually became even more laconic. He refrains from mentioning Hájek's astrological opinion since he does not want to mix it with his own, both because it is not based on firm evidence and everyone is inclined towards these opinions according to their natural disposition (ibid., 286). He also declines any treatment of the third part of Scultetus’ work, which is on astrology, unlike the first two parts, which satisfy the higher norms of appearances and truth.