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