A Spanish study of the 1572 nova: Jerónimo Muñoz and his Book on the New Comet

Introduction

In his Astronomia Nova, Kepler attributes to Divine Providence the fact that he devoted his time and energy to the study of planet Mars, ¹ because had Tycho asked him to focus on any other astronomical problem in 1600, he would not have started walking the path that finally led to his revolutionary new foundations for astronomy. If one looks at the decades in which Tycho and Kepler worked, it is not difficult to come to the conclusion that God was really interested in helping these astronomers to advance their field. For it was not only Kepler’s ocupations that seem to have been guided, but also the astronomical events that framed their entire effort: we have to go back to the mid-14th century, or forward to 1743, to find a comet as bright as the one they observed in 1577. The one from 1556—mentioned in this Book—was just one magnitude below. ² But most importantly, of the eight historical supernovae, two of them were seen in a space of less than 30 years: 1572 and 1604 were the years of the so called Tycho’s and Kepler’s supernovae, respectively.These events were instrumental in the final demise of two longly held Aristotelian principles regarding the nature of the heavens: the idea that celestial objects were moved by solid spheres, and the notion that the supra-lunar part of the cosmos was one where no change ocurred, only ever repeating cycles.

Víctor Navarro Brotons, probably the most important scholar on Jerónimo Muñoz today, says that at least 45 authors contemporary to the 1572 nova mentioned it in their work. ³ It was, as I said, an extremely rare event, one filled with possibilities for the renovation of astronomy. Of course, not all of them made careful observations, or were creative enough to use them to challenge the received tradition. Master Jerónimo Muñoz was not one of these. In his work, he not only indicates the location with great accuracy, but he also hints at some aspects of the nova’s development during its first months, as well as placing it in the more general discussions about the nature of the heavens, their relation to the elements, and their significance to earthly events.

This short article serves as an introduction to the English translation of the Book on the New Comet (which will be found as an appendix to the on-line version of the article). As will become apparent from the sources I use, I draw much from the work of Víctor Navarro Brotons, whom I mentioned earlier. The reader with a good command of Spanish can refer to the appendices in his 1981 reproduction of the Book, or to his more complete and scholarly Jerónimo Muñoz; matemáticas, cosmología y humanismo en la época del Renacimiento (2019). While the latter encompasses Muñoz’s entire career and interests, the former contains the first English translations of selected passages of the Book.

Jerónimo Muñoz and astronomy

Jerónimo was born during the second decade of the 16th century, in the city of Valencia, near the Mediterranean coast of Spain. During the 1530s he studied at the municipal University, where in 1537 he graduated as Bachelor of Arts. He learned Mathematics with Oronce Finé at the Collège Royal in Paris, and took private lessons on the same subjects with Reiner Gemma Frisius in Louvain. Muñoz had a profound knowledge of Hebrew, so much so that in the late 40’s he went to the University of Ancona to teach that language. While in Italy he became part of Cardinal Poggio’s retinue: he mentions at least one travel from Zaragoza to Rome, during which he carried out cartographical studies in Italy, France, as well as Spain. ⁴ In the last section of the Book on the New Comet Muñoz tells us that “[. . .] on the first days of February, in 1556, I observed in Elche a comet that lasted for more than 50 days [. . .],” so that date is the terminus ad quem for his return to Spain. Whatever the precise date is, by 1563 he was teaching Hebrew at his alma mater. Two years later, on June 1565, he was also named Professor of Mathematics there. In 1578, and although he had one of the best salaries in the University, he decided to move to the University of Salamanca, with a better salary and, undoubtfully, a much more prestigious position. There, he taught Euclidean arithmetic, geometry and perspective, Ptolemaic astronomy, astrology, and geography, the Alfonsine tables, and Peuerbach’s solar and lunar theories. It is also likely that he taught Copernican astronomy and the Prutenic tables, as well as Hebrew. He continued to teach there until his death in 1591.

Muñoz’s academic life shows that he was a typical example of the Renaissance polymath: as we saw, he was very well versed in several languages, as well as in various mathematical disciplines. It is of particular interest to us to look into his relationship with astronomy and astrology. For reasons that we will discuss later, most of Muñoz’s works never got to be printed. Many of the autographs of these works are still extant, while others are only preserved in copies.

The manuscript list shows a prevalence of astronomically related subjects: there is a commentary to the second book of Pliny’s Natural History, a translation with a commentary of Theon’s commentary to the Almagest, a commentary to Alcabitius’ treatise on judiciary astrology, and a Theorica Planetarum. There is one work on the construction of astronomical rings and one about the existence of celestial spheres. Finally, he wrote an introductory work of astronomy (astrologicarum) and geography. ⁵ As these names indicate, Muñoz was interested in the variety of fields that comprised the celestial disciplines of the day. The list also contains several works on mathematical topics which are also related to, and served as the technical basis of, these cosmological, astronomical, and astrological sciences.

Although the Book on the New Comet presents a fundamentally anti-Aristotelian stance regarding the nature of (at least) the 1572 comet and its implications, this does not mean that Muñoz ever abandoned the core cosmological principles which had prevailed in the astronomical communities before the end of the 50th century. Both in the Commentaria Plinii libri secondi and in his Astrologicarum et geographicarum institutionum libri sex, Muñoz explains the basic structure of the universe in the same way we could expect to find in Aristotle’s Physics, or in the first books of Ptolemy’s Almagest: the Earth is a round body, located at the center of the cosmos, and the Earth’s size with respect to that of the universe is as that of a point to a sphere around it. The general explanation of the celestial motions also follows the same pattern, and we can find there the typical introductory explanations about the daily and annual motions any traditional Aristotelian would present in those days.

There are, nevertheless, critical aspects of Muñoz’s reading of Aristotle, whom he regarded as an inferior author when it comes to astronomy: in the Book he says that the Stagirite could not understand the doctrines of Anaxagoras regarding comets because he was not an astronomer nor did he possess “[. . .] the principles to understand the doctrines of the Chaldeans and the Egyptians.” ⁶ Unlike Aristotle, he thinks that the regions beyond the Moon are filled with air, and that this element has a passive quality that allows for it to receive the influence of the Sun and the stars, and thus serve as a causal connection between the celestial and the beings down here. ⁷ The most important deviation, however, is his denial of the physical reality of the spheres, which is explained in his Utrum sint plures orbes necne. The main reason he adduces against the traditional position is that it goes against the letter of the Sacred Scriptures, and against the doctrines of many of the Fathers and venerable writers such as S. Ambrosius, S. Chrysostom and Bede. Indeed, in Genesis we read that God created one firmament, and not many. He goes on to give several additional arguments. One of the most interesting ones is that which notes that if the Moon moved on a physical epycicle, as an Aristotelian interpretation of Ptolemy suggests, then the Moon should not always show us the same face. He also indicates that if we saw the planets and stars through several “layers” of spheres, then we would see them change thir appearances in the same way a coin does when it is at the bottom of a well, due to the optical effects caused by the spheres. ⁸

Muñoz’s conservative position regarding the disposition of the Earth, the planets and the Sun should in no way be taken as a sign that he was not aware of the alternatives that were being discussed at the time in Europe. In his commentary to Theon Muñoz shows, yet again, that his astronomical principles were in line with Ptolemy’s. However, when he arrives at the section dedicated to Almagest I 6–7, Muñoz explains the Copernican system (see Figure 1). While he admits that the theory of relative motions could explain how a moving Earth is compatible with our perception of a moving sky, he discards the Copernican theory based on philosophical grounds. According to Muñoz, Copernicus’ main argument for the rotation of the Earth is that which gives preeminence to the “container”—that is, the sphere of the fixed stars—rather than the contained—that is, the Earth. This preeminence translates to immobility, so it is expected that the Earth should rotate once a day, rather than the entire sphere. ⁹ If this is the case, Muñoz asks, then how does Copernicus explain that in the case of the Earth-Sun system, it is the container—the annual sphere of the Earth—that which moves, instead of the contained—the Sun–? ¹⁰

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Figure 1.

Diagram of the Copernican system by Muñoz, in his commentary to Theon’s Commentary of the Almagest. The manuscript is in the library of Naples (Napoli, BN, VIII C 33, s. XVI, f. 21r–300r), and a scanned version is available at the Ptolemaeus Arabus et Latinus Project website. The diagram is in fol. 35r.

Muñoz and the 1572 nova

The most important contribution to early modern astronomy Muñoz made was probably his account of the nova which appeared in Cassiopeia in 1572. The chronology given earlier shows that it was during the middle of his period as Professor in Valencia that he observed it. He tells us that he was alerted of the apparition of the new object by some shepherds in the region of Onteniente, to whom he had been teaching some basic astronomical notions. This reveals an interesting aspect of his teaching career: it seems that he not only taught to the more advanced students in the city, but that he was also available for broader publics whose common knowledge of the sky he respected. In chapter II he says that among them there were some “[. . .] that were very knowledgeable in them [the stars] [. . .].” He is sure that the nova could not have appeared before November 2nd, since on that day he was teaching these people. He received the news of the new star on November 18th, but he observed it for the first time on December 2nd. Nevertheless, it was known in the region since at least November 12th that there was a new star in the sky, and there are testimonies that suggest that it was first detected in Europe on November 6th, if not before. ¹¹ The most famous observation of the nova of 1572 is Tycho’s, which took place on November 11th. ¹² The last observation of the nova that is noted in the Book corresponds to January 7th, 1573, although the nova itself was visible until March 1574, ¹³ and maybe even May. ¹⁴ From the Book’s prologue, as well as from a letter from Muñoz to Bartholomaeus Reisacherus (a copy of which, via Tadeáš Hájek, or Hagecius, ended up in Brahe’s power), we get to know that it was written by the request of Phillip II, King of Spain. So it is understandable that Muñoz wanted to fulfill the King’s curiosity as soon as possible, and to answer what were apparently the most important concerns the ruler and his court had regarding the strange phenomenon, i. e., what was its nature, where was it located and, most particularly, what was its meaning in terms of astrological prognostications: Muñoz has the precaution of explicitly saying, in the very first line of the prognosis, that the phenomenon had no negative implications for the King’s life. Thus, because it did not need to, the Book makes no attempt at carefully following the development of the nova’s magnitude. Instead, it merely states that when it appeared it was as bright as Jupiter, even almost as bright as Venus, but that on the first days of 1573 it had already fallen to below Jupiter’s magnitude. Nevertheless, this might not be the only reason Muñoz published the Book without a deeper study into the phenomenon’s behavior. For an even superficial reading of the work reveals that the main point he was trying to make was that this “comet,” if properly studied, destroyed one of the fundamental assertions Aristotelians had held, that is, that the heavens are unchanging and eternally the same. ¹⁵ His study of the nova’s parallax, like Tycho’s, concluded that the phenomenon was beyond the Moon. In fact, Muñoz considers that the limit for the detection of parallax is the distance to the Sun. That he chose the distance to the Sun as the minimum distance where an object with no parallax can be detected should not go unnoticed: it does not only go against the traditional lunar limit, but also ignores the fact, known by him, that Venus and Mercury, which are closer to the Earth, also show no parallax. So, given that to criticize the Aristotelian view he only needed what he already knew by January or February, that is, that the object had no parallax, and that it was changing its appearance, there was no point in waiting more time.

It is in his anti-Aristotelianism where we can find, without a doubt, the origin of all the criticisms he received from the “[. . .] Theologians and Philosophers [. . .].” ¹⁶ Given these problems, he says, he decided not to publish the entirety of his studies on the nova, and in fact vowed not to publish anything else, a promise he very rarely broke.

The Book on the New Comet

In the preface to the Book, Muñoz adresses the King, pointing to the Aristotelianism prevalent in the court’s philosophers as the main source for the error and ignorance regarding the new phenomenon. Muñoz presents a contrast between Anaxagoras and Aristotle, where the first one—“[. . .] a most important philosopher and mathematician [. . .]”—is presented as the superior on astronomical matters: Aristotle did not understand his doctrines because of “[. . .] not being an astronomer, nor possessing the principles to understand the doctrines of the Chaldeans and the Egyptians,” meaning by these the principles of geometry and arithmetic.

In this context, Muñoz vaguely conflates the doctrines of Democritus and Anaxagoras about the origin of the cosmos with his interpretation of the Biblical text in Genesis: he explicitly says that Aristotle, unlike these two, rejects the idea that the universe originated in Chaos or, as Moses called it, “tohu vabohu,” a transliteration of the Hebrew in Gen. 1:2 for the expression “without form and void” (KJB).

Muñoz also introduces the astrological aspect of his little treatise by presenting his underlying theory of astrology. He supports the classical position where the celestial bodies exert an influence in man that limits to his physical aspects. Because the emotions and passions are intrinsically connected to the human body, any causal influence of the celestial bodies on it will necessarily have an effect also on the person’s complexion. Since most men are governed by their passions, and very rarely conduct themselves according to reason and, in general, the higher spiritual power they possess, this means that these influences will have a noticeable effect in human affairs. ¹⁷

The first chapter is a general description of the main celestial bodies that were the subject of astronomy in his times. He begins with the Sun and the Moon, and then continues with the five planets.

When he begins his exposition on the fixed stars, he refers to the Hipparchian alignments Ptolemy describes in the Almagest ¹⁸ and says that, as Ptolemy did in his times, he also has found that those stellar configurations still hold for his own century. He then classifies the fixed stars into six different magnitudes, giving a detailed list of the ones that belong to the first, and only indicating the quantity of stars that belong to each of the other magnitudes. Furthermore, he mentions the existence of “darknesses and nebulae [. . .] seen as stains or spots.” He ends the chapter with a brief explanation of how he determined the value of precession by basically repeating the procedure that Ptolemy followed in the Almagest.

In chapter 2 Muñoz gives us the story that I mentioned above, about how he got to know about the nova. He goes on to present a probable astrological cause for its apparition, and gives some details about the evolution of the nova’s brightness. There is a thorough description of the location of the phenomenon within the Cassiopeia constellation. In this context, he gives a simple procedure to calculate the nova’s declination.

Chapter 3 deals with the method to calculate the apparent position of the nova, given some basic data obtained by observation. Using procedures he likely learned from Regiomontanus—he constantly refers to some of the latter’s procedures in the Tabula Primi Mobilis and the Tabulae Directionum, he is able to calculate the ecliptic coordinates of the nova. He concludes the chapter by stressing that the found position of the nova has remained unchanged for the entire duration of the phenomenon.

After this, Muñoz inserts a pedagogical chapter, where he gives a brief explanation of parallax. He begins by distinguishing between the true and the apparent location of a celestial body. Given that the center of the Earth is, as Ptolemy had proven, also the center of the universe, then it is natural to use it as the proper reference for locating any body. Through a series of very basic geometrical steps, he concludes that, from the point of view of an observer on the surface of the Earth, the apparent location of a body will always be lower than the true one.

Nevertheless, because the difference is directly related to the distance from the celestial body to the center of the Earth, and given that the distance from it to the Sun, Mars, Jupiter, and Saturn is so great, then in those cases the difference between the true and apparent locations will be negligible. The same also applies, of course, to the case of the fixed stars.

After these introductory clarifications, Muñoz goes on to give a geometrical explanation of how parallax depends not only on the distance to the Earth, but also on its altitude: he carefully explains why the closer the object is to the horizon, the greater the effect of parallax will be.

In Chapter 5 Muñoz comes back to the case in study and determines that the phenomenon is not a fixed star nor a planet. Regarding the first, it seems that to Muñoz the term “fixed star” must be reserved to a body that remains unchanged through time not only in its relative position to the other stars, but also in its appearance. By the time he wrote the Book, the nova had started to decrease its brightness, so although he was aware that it was following the motion of the fixed stars, always remaining at the same distance to the rest of stars in Cassiopeia, he decided to classify it under the category of comets, which was one that could, if it had to, encompass objects that did not move in the celestial sphere. It should also be noted that Muñoz states that the reason the phenomenon’s magnitude changed had nothing to do with a variation in its distance to the Earth, or due to any other motion, but instead it can only be due to the fact that it is “disappearing or dissolving.”

Muñoz was certainly aware that the new phenomenon was a very unusual one, for he devotes chapter 6 to explain the various kinds of comets previous authors described, only to conclude that “In no author do I find a comet like this, which looks more like a star than a comet [. . .].” He nevertheless says that it was not unprecedented, since Ptolemy, Pliny and Lucan had already mentioned the rare occurrence of fixed comets.

Chapter 7 and 8 are a discussion regarding Aristotelian meteorology: how the different parts of the air are divided, and how this affects the formations of comets and other phenomena. His conclusion is that comets are formed not in the air, like Aristotle wanted, but in the sky. He finishes the chapter with a suggestive line: he says that comets “[. . .] possess the principle of their motion, different to that of the planets and from the first moved [orb]. Although our comet has, until now, invariably kept the laws of the motion of the first moved [orb], as if it was a fixed star.”

In chapter 9 Muñoz gives a very succinct explanation of Ptolemy’s observations and procedure for calculating the inclination of the lunar deferent, and the value for the lunar parallax. This discussion continues in chapter 10, where he gives a parallax table computed by himself, in order to be able to carry out the different methods for calculating parallax that he will propose in the following chapters.

In chapter 11 Muñoz gives a method for finding the parallax of a circumpolar object, using as data observations of upper and lower culminations. Given that the comet, as seen from Europe, was circumpolar, this will allow him in chapter 12 to conclude that it shows no parallax, and that it is therefore beyond the Sun. Assuming this distance, and an angular size of more than 8 minutes for the nova, he calculates the proportion between its volume and the Earth’s.

Chapter 13 presents a method for finding the parallax of rising and setting phenomena. It is not clear to me what reason did Muñoz have to include this section in the Book, since it was not necessary for the treatment of the subject matter, the Book was aimed to: the nova was, in Spain, a circumpolar phenomenon. Whatever those reasons were, the method he presents is nevertheless deeply flawed, and would have never allowed him to obtain any parallax from observations of phenomena that indeed showed some.

Chapter 14 is, as was chapter 3, a section where Muñoz explains how to apply various geometrical methods to go from some data to a desired result about the object’s location. In this case, on how to go from the apparent declination and parallax to the true ecliptic position of a circumpolar phenomenon. After this, he briefly explains how to calculate the geographical longitude of a given location from lunar observations.

Finally, chapter 15 discusses how the motions of the planets and their relative positions influence the formation of comets and, in particular, the comet of 1572.

The last three sections are dedicated to the relation between comet and the events they predict here on Earth. The first one is a short description of the criteria an astrologer must have in order to properly obtain a good prognosis from a comet. In this respect, he follows mainly Ptolemy, but also Alī ibn Riḍwān. The second one is focused on the predictions he makes based on the position, behavior, and appearance of the 1572 comet. Finally, to give some support to his prognosis, he mentions what predictions he had made when he observed the 1556 comet, and how they came to pass. It should be noted that in 1578 Muñoz published the Summa del Prognostico del Cometa; y de la eclipse de la Luna, whose complete title ¹⁹ can be translated as Summary of the prognostic of the comet and the lunar eclipse which took place on September 26, 1577 at 12:21, where the comet was caused by said eclipse. As the title indicates, the brief text of just eight pages is an exercise in astrological considerations, much as the last chapters of the Book on the New Comet.

Muñoz’s recognition and the reception of the Book

Muñoz had a deep influence in the Spanish mathematical community of the time. Gabriel Serrano, his successor at the University of Salamanca, maintained correspondence with Clavius. In one of his letters, he described Muñoz as an expert both in mathematics and in theology and compares him to the sages of ancient times. ²⁰ Serrano was in turn succeeded by Antonio Nuñez Zamora, who wrote a book about the 1604 nova, the Liber de Cometis, in quo demonstratur Cometam anni 1604 fuisse in firmamento. As the title indicates, the work defends a position at least similar to the one Muñoz presented in the Book. Muñoz also had followers in the University of Valencia, where he studied and taught for many years: Marco Antonio Palau, as Nuñez Zamora, also wrote a book on the 1604 nova presenting similar theses as Muñoz. ²¹ In his latest work on Muñoz, Navarro Brotons adds many more names, most of them of a lesser importance: among others we can mention Pedro Ruiz, who worked on sundials and colaborated with Muñoz in his works on trigonometry; Bartolomé Antist, who published some minor works on astrology; Juan Cedillo Díaz, even if he accepted Copernican heliocentrism, defended Muñoz’s ideas about the physical causes of planetary motions. ²²

Outside Spain, though, it was his study on the 1572 comet that was responsible for Muñoz’s fame. As I said earlier, the Book was written and printed with haste. Nevertheless, and probably because of the excitement its subject matter arose in the mathematical circles of the time, it seems to have enjoyed some degree of success: by 1574 it already had a French translation by Guy Lefèvre. ²³ More over, his observations were evidently done with care, as Tycho himself discusses them in his Astronomiae Instauratae Progymnasmata ²⁴ and shows that, although they did not have the precision his own instruments allowed, they were nevertheless very accurate.

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