The emergence of modern astronomy – a complex mosaic: Part V

Part I Part II Part III Part IV

As I already mentioned in Part II, Copernicus wrote his first work on his heliocentric theory in about 1510, the Commentariolus, which remained in manuscript but seems to have enjoyed a fairly wide distribution, as we will see later. However, Copernicus was not the only show in town in the astronomical world of the sixteenth century. Before I continue with his story I will look at what else of significance was taking place.

In Part I we learnt how Toscanelli took a new approach in his treatment of comets, viewing them as objects to be astronomically observed and not just as meteorological phenomena as the Aristotelian had; his lead was followed in Vienna by Peuerbach and Regiomontanus. In the 1530s there was a series of spectacular comets, which attracted the attention of the new class of European astronomers and their observations led to more new developments.

Book_of_Miracles

Girolamo Fracastoro (c. 1477–1553) was the first European to draw attention to the fact that a comets tail always points away from the sun in his Homocentrica (1538); a seemingly trivial discovery but one that correctly interpreted played an important role in re-determining the role of comets.

Titian_Girolamo_Fracastoro

Portrait of Girolamo Fracastoro by Titian, c.1528 Source: Wikimedia Commons

Peter Apian also independently the same discovery in his Astronomicum Caesareum (1540). Strangely the discovery is usually only attributed to Apian.

Warkocz_komety_Astronomicum_Caesareum

Apian’s depiction of comet’s tail facing away from the sun Source: Wikimedia Commons

The Fracastoro/Apian discovery had been made much earlier by the Chinese but this was not known in Europe. Johannes Schöner was stimulated by the situation to publish Regiomontanus’ work on determining the parallax of a moving comet, a problem that was taken up again in a correspondence between John Dee and Tycho Brahe later in the century. Comets were no longer just astrological harbingers of doom but had become objects of astronomical interest.

In a European wide debate that included Copernicus, amongst others, both Gerolamo Cardano in Milan and Jean Pena, Royal Professor of Mathematics in Paris, came up with a new comet concept. Comets were supralunar and transparent; they functioned like a lens that focused the sunlight, the focused light being then the tail of the comet. A serious breach had been made in the accepted Aristotelian cosmology. Not only were comets supralunar but they were also supralunar object that demonstratively changed, an affront for the Aristotelian concept of a perfect, unchanging heaven.

Of course, these new radical ideas were not instantly accepted by the European astronomical community and it was a community, which discussed and debated their observations and theories with each other. However, it stimulated that community to plan observation programmes to be carried out the next time comets would appear in the heavens over Europe. Unfortunately, when the next spectacular comet appeared over Europe in 1556, one generation of capable astronomers was already dead and the next one was still in its childhood (Tycho was ten and Mästlin was six years old) or in the case of Kepler not yet born.

PII: 0160-9327(79)90035-8

An astronomical broadsheet by Paul Fabricius, showing the map of the 1556 comet’s course Source: Wikimedia Commons

Urania was, however generous, delivering a supernova in 1572 and a great comet in 1577 for the delectation of the eager European community of astronomers.

468384main_pia13119-4x3_946-710

Red circle upper left hand corner remnant of 1572 supernova Source: Wikimedia Commons

The discovery, observation and analysis of these celestial phenomena are, in the popular history of astronomy books, almost exclusively attributed to Tycho Brahe. This attribution creates a distorted picture of what actually happened. Astronomers, amateur and professional, all over Europe observed both the supernova and the comet, attempted to determine parallax and thus the distance of them and wrote up and published their results and opinions is a veritable flood of publication, largely pamphlets.

The results covered a wide spectrum, from definitely supralunar over non-measurable parallax to definitely sublunar. Tycho, Michael Mästlin and Thaddaeus Hagecius ab Hayek (1525–1600), all influential astronomers, all determined that the observed phenomena were clearly supralunar. For those who have not come across him Thaddaeus Hayek was professor of mathematics at the University of Prague and personal physician to the Holy Roman Emperor Rudolf II and played a central role in bringing both Tycho and Johannes Kepler to Rudolf’s Court in Prague.

800px-THajek

Thaddaeus Hagecius ab Hayek Source: Wikimedia Commons

In the acceptance of the fact that the celestial phenomena of the 1570s were supralunar and thus demolished a large chunk of Aristotelian cosmology i.e. that he heaven are perfect and unchanging, at the time, Mästlin’s word counted more than Tycho’s but the placet of widespread acceptance was lent to this opinion through its confirmation by the leading Catholic astronomer, Christoph Clavius (1538–1612). We will return to the role of comets in the emergence of modern astronomy in a later post but before I depart here I want to comment on the categorical rejection of the supralunar nature of the supernova of 1572 and the comet of 1577 by the Nürnberger artist and astrologer/astronomer Georg Busch (ca. 1530–1579).

Born in Nürnberg, Busch moved to Erfurt where he worked as an artist and from about 1550 as an astrologer/astronomer. Busch published two books on the 1572 supernova, which he consistently referred to as a comet: Von den Comet, welcher in diesem 1572. Jar in den Monet Novembris erschienen, Erfurt, 1572 (On the Comet, which appeared in this Year of 1572 in the Month of November) and Entschuldingung and Schutzrede Georgij Busch… Erfurt, 1573 (Apology and Defence of Georg Busch…(the title goes on and on). The second pamphlet is a defence against criticism. Both publications went through several editions showing that the ‘modern’ astronomers didn’t by any means have the field to themselves. Busch’s publications even made it into Tycho’s annotated catalogue of the comet publications. What I personally love is Busch’s description of the nature of comets:

“…the comet was composed of a sort of obnoxious gas generated by human sin, which floated heavenward until ignited by the wrath of God. As it burned the comet became a prolific celestial polluter, showering its effluence widely over Earth and thereby causing pestilence, Frenchmen, sudden death, bad weather…”

Observant readers might have noticed that Fracastoro’s account of the direction of comet’s tails was in a book entitled Homocentrica.

The central argument of this publication was a rejection of the epicycle-deferent model of Ptolemaeus and a return to the homocentric spheres model of the cosmos propagated by Eudoxus and above all Aristotle. This is, of course, highly reactionary in the sixteenth century when most important astronomers were moving away from Aristotelian orthodoxy but Fracastoro was a well-known and highly respected author so his opinion was by no means rejected out of hand. Later in the century Christoph Clavius (1538–1612), the defender in chief of Ptolemaic astronomy, regarded Fracastoro’s homocentricity as a greater threat than Copernicus’ heliocentricity.

It should be clear that far from representing a boring, orthodox conformity that was shaken out of its torpid stupor by Copernicus publishing his heliocentric hypothesis, the sixteenth century debate on astronomy and cosmology was a lively exchange of ideas and concepts some old and some new.

 

 

 

 

 

 

 

17 Comments

Filed under History of Astronomy, History of science, Renaissance Science

17 responses to “The emergence of modern astronomy – a complex mosaic: Part V

  1. Ray

    Intersting post. Your discussion of Fracastoro’s Homocentrica led me to James Lattis’s “Between Copernicus and Galileo: Cristoph Clavius and the Collapse of Ptolemaic astronomy.” Based on the discussion therein a number of things seem notable.

    First of all, it’s notable that Clavius seemed to take the homocentric model at least as seriously as the Copernican model despite the fact that, at least as far as I can tell, Copernicus had significantly more followers contemporary to Clavius than did Fracastoro. You’ve already mentioned several early Copernicans in your series thus far, of whom presumably Maestlin was presumably the most prominent when Clavius was writing. (Here I’m assuming you’re basing your statement on Clavius’s views on the 1581 edition edition of his Commentary on the Sphere of Sacrobosco, which is the work cited by Lattis.) In contrast, I can’t find any clear examples of homocentrists after Fracastoro (although Lattis speculates Clavius’s colleague Benedict Pereira may have been one.) I personally wonder whether this exemplifies premodern attitudes that weight ancient wisdom more highly in comparison to cutting edge research than we are used to today — homocentrism seems to have had a lot of ancient and medieval advocates (most notably Aristotle and Averroes.)

    Second of all, from Lattis’s summary, Clavius’s refutation of Fracastoro seems like solid scientific work. I especially liked the discussion of the varying apparent size of the sun and moon and how Fracastoro attempted to wave this away by positing that their appearance is modified by sublunar optical effects. Clavius rightly points out that if this were the case, the appearance of the fixed stars would be affected as well, but it isn’t. (The example I would use here would be annular and total solar eclipses, since this phenomenon seems nearly impossible to explain by sublunar optical effects, and much more striking and less prone to measurement error than the examples Clavius apparently gives.) This particular 16th century scientific debate is certainly something I’d be interested in seeing more detailed discussion on (perhaps in a future post here, one might hope.)

    Finally, I do have one nitpick regarding the conclusion of the current post:

    It should be clear that far from representing a boring, orthodox conformity that was shaken out of its torpid stupor by Copernicus publishing his heliocentric hypothesis, the sixteenth century debate on astronomy and cosmology was a lively exchange of ideas and concepts some old and some new.

    I don’t entirely disagree with the statement. If nothing else, what you’re denying seems to be such an extreme position that it can’t help but be false. But it seems odd to support a statement concerning the state of astronomy before Copernicus by appealing to debates that happened mostly inthe 1570s after Copernicus had published his De Revolutionibus. Also, Fracastoro, as you note, is a bit of a reactionary example for illustrating the “liveliness” of the pre-Copernican astronomical debate. Might one instead look at Homocentrica and conclude that medieval astronomy up to the time of Copernicus was more concerned with the sort of theological concerns and speculative system-building philosophy that motivated people like Aquinas, than it was concerned with modern scientific values like simplicity and empirical accuracy? Obviously, an extreme position that astronomy changed overnight with Copernicus is indefensible, but might it perhaps be better to treat stereotypes of Medieval astronomy as exaggerations rather than outright fabrications?

    • modern scientific values like simplicity and empirical accuracy?

      Hmmmmm…..

      Not that I entirely disagree….

      • Ray

        Michael,
        I take it that this is meant as some sort of a criticism of my comment. I’m afraid I’m not enough of a mind reader to intuit the nature of your disagreement though. Could you please elaborate?

      • Simplicity is just about useless as a scientific criterion, thanks to its subjectivity. I could write an essay on that, but I won’t. For an amusing example, I’ll just mention Francis Crick’s punctuation-free genetic code—much more elegant than the actual genetic code.

        But apart from that, it’s not modern! Which is simpler, the circle or the ellipse? Which is simpler, a bunch of concentric circles, or a bunch of circles with different centers? Simplicity was clearly something the ancient Greek philosophers prized. (Hey, remember “everything is water”?)

        Empirical acccuracy is a moving target. It seems particularly odd to claim it as a modern value when discussing astronomy, since the Almagest is almost a textbook example of a serious and largely successful stab at a predictive theory. (And you could make a case for the Babylonians, too.)

        Sufficient unto the day is the accuracy thereof. Buchwald’s “Rise of the Wave Theory of Light” has a nice discussion in chapter 1, with regard to double refraction (see especially section 1.3).

        QED is often touted as the most accurate modern theory, with agreement to 12 decimal places in some cases. On the other, it predicts a vacuum energy density more than 50 orders of magnitude too large. I think Kuhn got it right: any significant scientic theory always has spots where theory grinds uncomfortably against experiment.

        As I said, I don’t entirely disagree. It would be absurd to claim an equivalence between, say, the 12th and 21st century standards of accuracy. But I don’t think that as a scientific value, we can claim it as a modern innovation.

      • Ray

        I agree that the notion of simplicity I allude to needs more clarification. Nonetheless, some form of the principle clearly does play a role in modern empirical science (e.g. quality of fit statistics are adjusted for the number of free parameters in the model.)

        Moreover, I disagree that simplicity played anything like that role in the reasoning of Aristotle and those influenced by him. Aristotle didn’t argue that the motions of heavenly bodies have a higher prior probability to be circular because this was the simplest motion. He argued, with claimed apodictic certainty, that uniform, eternal, circular motion was the only possible motion that things like the heavenly bodies could have. Also, while it is true that a circular orbit is simpler than an elliptical one all else being equal, once enough deferents, equants, and epicycles are added to fit the data, the result is a cosmology that is significantly more complicated than that of Kepler. Likewise, once you’ve added enough detail to a homocentric model to predict annular and total solar eclipses, the result is more complicated than the system of Ptolemy. Because assumptions like circularity of heavenly motions came not from a preference for simplicity, but from arguments that claimed to irrefutably rule out the alternatives, they were not abandoned immediately when it turned out that working from these assumptions introduces more complexity than it saves.

      • I agree that the notion of simplicity I allude to needs more clarification.

        I’ll be interested to see your clarification. Personally, I don’t believe the notion can be “clarified” of its inherent subjectivity. Not without huge dollops of question-begging and ahistoricism.

      • Ray

        Simplicity is just about useless as a scientific criterion, thanks to its subjectivity

        I don’t dispute that simplicity as applied in science is subjective (except in limited cases where it’s part of a standard data analysis technique like Chi squared analysis or MaxParsimony.) Rather, I dispute your claim that subjective criteria are useless in science. (Speaking of which, what do you think of peer review?)

        On the contrary, I would say that all attempts to devise a formulation of the scientific method freed of human subjectivity have failed. Real science is and always has been done by humans who use their own subjective judgement in many matters. In the specific case of a simplicity/parsimony criterion, it is necessary to choose between the literally infinite number of theories that are compatible with any finite data set. What is your alternative?

    • As so often your comment is a mixture of false readings, strawmen and unsubstantiated claims.

      …Copernicus had significantly more followers contemporary to Clavius than did Fracastoro.

      I have absolutely no idea how many people subscribed to a homocentric sphere theory of the cosmos in the last quarter of the 16th century and that is not the point. The homocentric sphere theory has a long and prominent history in astronomy and its renewed revival was seen by Clavius, as a greater threat to the Ptolemaic system than Copernicus’ heliocentricity. As for Copernicus’ supposed ‘significantly more followers’ they could at the time be counted on the fingers of one hand.

      I personally wonder whether this exemplifies premodern attitudes that weight ancient wisdom more highly in comparison to cutting edge research than we are used to today

      This is exactly Copernicus’ attitude. Copernicus has, quite correctly, been called the reluctant or conservative revolutionary. The only information that we have from Copernicus about his motivation for his work is that he was trying to remove the equant point from Ptolemaic astronomy because it, in his opinion, stood in contradiction to the so-called Platonic axioms, that is that that celestial motion is uniform circular motion. A return to the Platonic axioms was also the motivation of those throughout history, who supported a homocentric spheres model. Copernicus was not looking towards the future but back to antiquity, which is why in the end his heliocentric model ended up more complex than the geocentric Ptolemaic model of Peuerbach.

      The standard popular presentation of the so-called Copernican Revolution is that the Ptolemaic geocentric model ruled undisturbed and unchallenged for 1400 years until Copernicus burst onto the scene. This is simply not true as astronomy was continually changing and evolving throughout the Middle Ages and in particular, as I have sketched in the 16th century.

      But it seems odd to support a statement concerning the state of astronomy before Copernicus by appealing to debates that happened mostly in the 1570s after Copernicus had published his De Revolutionibus.

      The main debate on the nature of comets, in which Copernicus took part, took place in the 1530s before the publication of De revolutionibus and the 1570s were where the results of that debate where checked against the observable phenomena.

      …conclude that medieval astronomy up to the time of Copernicus was more concerned with the sort of theological concerns and speculative system-building philosophy that motivated people like Aquinas, than it was concerned with modern scientific values like simplicity and empirical accuracy?

      Medieval and Renaissance astronomy is concerned with the mathematical models used to generate celestial data for astrology, astro-medicine, cartography and navigation and not with “theological concerns and speculative system-building philosophy.” Copernicus cannot in any sense be considered to be “concerned with modern scientific values like simplicity and empirical accuracy.” As already pointed out, because of his insistence on the Platonic axioms, his system was more complex than the prevailing Ptolemaic, geocentric system of Peuerbach and because he used the same corrupted Ptolemaic data in no way more accurate.

      • Ray

        As for Copernicus’ supposed ‘significantly more followers’ they could at the time be counted on the fingers of one hand.

        I don’t see how that contradicts what I said.

        To elaborate, from what I can tell, we have unambiguous writings from Rheticus, Digges, and Maestlin implying that they were supporters of Copernicus before 1581, as well as slightly more ambiguous, but still generally positive references to Copernicus’s cosmology from Frisius, Stadius, Dee, Recorde, Feild, and Dasypodius.
        These positive references would be joined, within a number of years that can be counted on one hand, by writings from Benedetti, Bruno, Zuniga, and Rothmann. Christian Wurstisen is also generally suspected of having been a Copernican at this time, based on a reference in Galileo’s dialogue.

        In contrast, I can’t find a single example of a follower of Fracastoro in the same period as well supported as even the weaker examples above. Even taking a pessimistic estimate (say only crediting Rheticus, Digges and Maestlin as followers of Copernicus before Clavius) 3 seems to me to be significantly more than 0.

        This is exactly Copernicus’ attitude. Copernicus has, quite correctly, been called the reluctant or conservative revolutionary

        I also don’t see how this contradicts anything I said, since my comment was about the state of affairs before Copernicus rather than the contributions of Copernicus. I was mostly trying to wait until you did a post focusing on Copernicus before offering any specific thoughts I might have on his work. But since you mention him, I will say that his work seems to me an interesting mix of modern and premodern ideas. He still holds to a lot of incorrect Aristotelian assumptions, but his innovations are sufficiently dramatic that it would be wrong to give Copernicus a back seat to Galileo, Kepler, and Newton in the story of the rise of modern astronomy, as some popular treatments tend to.

        The only information that we have from Copernicus about his motivation for his work is that he was trying to remove the equant point from Ptolemaic astronomy because it, in his opinion, stood in contradiction to the so-called Platonic axioms, that is that that celestial motion is uniform circular motion.

        Not sure I buy this. The clearest reference I could find to this motivation in De Revolutionibus was

        On the other hand, those who devised the eccentrics seem thereby in large measure to have solved the problem of the apparent motions with appropriate calculations. But meanwhile they introduced a good many ideas which apparently contradict the first principles of uniform motion.

        But, this occurs in a passage whose primary point seems to be to summarize existing disputes in Astronomy with the intent to imply that it is still an unsettled science. However, when Copernicus gets around to saying what there is to recommend his own system, it sounds decidedly more modern:

        Having thus assumed the motions which I ascribe to the earth later on in the volume, by long and intense study I finally found that if the motions of the other planets are correlated with the orbiting of the earth, and are computed for the revolution of each planet, not only do their phenomena follow therefrom but also the order and size of all the planets and spheres, and heaven itself is so linked together that in no portion of it can anything be shifted without disrupting the remaining parts and the universe as a whole.

        It sounds to me like he’s saying his theory predicts the data as well as that of Ptolemy, but is to be preferred because it has fewer free parameters.

        Presumably the basis for this claim is the fact, discussed later in De Revolutionibus, that orbital periods in the Copernican system monotonically increase with orbital size. (A similar relation is posited by Ptolemy, but Ptolemy unlike Copernicus had no independent way of determining relative planetary distances, except for the moon.) Moreover, Copernicus makes much of the fact that the general form of the orbits for the Sun and Moon, the inferior planets, and the superior planets all differ on Ptolemaic assumptions, while all the orbits of planets around the Sun are of the same form in the Copernican system.

        Other modern ideas I was impressed to find in De Revolutionibus: The roundness of the sun and moon is explained, like the roundness of the earth, by the self gravitation of these bodies (Is this the first time this argument shows up in the historical record?) Copernicus also uses the example of a moving ship (often credited to Galileo) to illustrate something like the relativity of motion.

        None of this is to deny that Copernicus believed that the planets were carried on their orbits by invisible, solid, perfect spheres, which moved with eternal circular motions — he clearly did believe that. But it seems like a stretch to consider that belief the primary, let alone the only motivation for his reform of astronomy.

        Medieval and Renaissance astronomy is concerned with the mathematical models used to generate celestial data for astrology, astro-medicine, cartography and navigation and not with “theological concerns and speculative system-building philosophy.”

        The context of the text you’re arguing against is trying to figure out what would motivate Fracastoro to prefer a homocentric theory over that of Ptolemy. Astrology, astro-medicine, cartography and navigation were certainly the primary motivations for doing astronomy at all, but they do not explain the popularity of homocentric models in the middle ages and early 16th century. Fracastoro’s model, like earlier homocentric models, was less accurate than that of Ptolemy and therefore less useful for cartography and navigation, and equally useless for astrology and astro-medicine.

    • Ray

      The example I would use here would be annular and total solar eclipses, since this phenomenon seems nearly impossible to explain by sublunar optical effects, and much more striking and less prone to measurement error than the examples Clavius apparently gives.

      On further research, it occurs to me that the distinction between annular and total solar eclipses may not have been widely noted among astronomers in the 16th century due to the rarity of a sufficiently careful observer finding himself in the direct path of a total or annular eclipse (and presumably almost no one was lucky enough to personally get a good look at both.)

      Thony, do you know of any clear evidence one way or the other?

  2. Laurence Cox

    One small point. The Wikimedia Commons image is a false-colour image made up of measurements at four wavelengths (3.6, 4.7, 12 and 22 μm), so the red colour indicates that almost all of the energy detected is at the longest of these wavelengths.

  3. Gavin Moodie

    Might not one start a justification of the value of simplicity in reason with William of Ockham’s principle of ontological parsimony?

    • There are surprisingly few instances of Ockham’s principle of ontological parsimony ever having been used in the history of science

    • Just this argument was used (at one point) by Mach and Ostwald to deny the existence of atoms.

      It’s not so easy to count up the number of “entities” in competing scientific theories. And simplicity in the broader sense is even more problematical.

      An analogy from propositional logic: a single logical connective (the Sheffer stroke) suffices; you don’t need and, or, not, if-then. The price you pay for this “simplicity” is unreadably complicated formulas.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s