The Danish astronomer Tycho Brahe (1546–1601) was, like Wilhelm IV of Hesse-Kassel a prominent aristocrat. In the sixteenth century Denmark was effectively ruled by an oligarchy of about twenty aristocratic families. Both of Tycho’s parents were members of the oligarchy. His father Otte Brahe was a privy councillor and his mother Beate Bille was a powerful figure at the Danish court. His uncle Jørgen Thygesen Brahe, who actually brought him up (it’s a complex story), was admiral of the Danish navy. Jørgen Brahe’s brother in law, Peder Oxe, was Steward of the Realm and as such the most powerful man in the kingdom. Put simply Tycho was born with every possible privilege. Naturally, it was expected that he would follow a career either in politics or the military or both. In 1559 he went to university to study law but he had already been bitten by the astronomy bug. He was immensely impressed by the fact that the solar eclipse on 21 August 1560 had been predicted, even if the prediction was off by a day. This was the beginning of his realisation that more accurate observational data was required.
In 1562, as was normal for a young Danish aristocrat, he set off on a study tour of the German universities. As before nominally to study law but he maintained his strong interest in astronomy. In 1563 he observed a conjunction of Jupiter and Saturn, which was his aha moment as far as the available planetary tables were concerned; both the Ptolemaic and Copernican tables were inaccurate, so he resolved to undertake something to correct this and began recording all of his astronomical observations. Having studied at Leipzig and Rostock, not just law and astronomy but also medicine and medicinal alchemy he returned to Demark in 1567. His father still wanted him to go into law but with the support of his quasi-uncle Peder Oxe, who had studied extensively and was a humanist scholar, Tycho was allowed to follow his desire to become a scholar.
Following further tours of Germany, where he acquired astronomical instruments, and the death of his father, which made him financially independent, in 1571 he set up his first observatory and alchemical laboratory at Herravad Abbey, with the help of another uncle Steen Bille.
In 1574 he published his first set of observations and began lecturing on astronomy at the University of Copenhagen. In 1575 he undertook another tour of Europe, partially in service of the Danish king. Tycho travelled throughout Europe meeting and talking to people looking at astronomical instruments and carrying out commissions from Frederick II (1534–1588). On this journey he visited Kassel and spent a week together with Wilhelm IV discussing astronomy.
Wilhelm had a collection of astronomical instruments of a wider range and better quality than anything Tycho had previously encountered. By this point Wilhelm had several years behind him, as a serious astronomical observer and could give Tycho much practical advice. He also discussed his plans for creating a new star catalogue, plans that had been postponed due to the death of his father and having to take responsibility for his land. Tycho inspired Wilhelm to go ahead with programme and Wilhelm inspired Tycho to settle down, build an observatory and carry out a similar programme. Due to a death in Wilhelm’s family, Tycho must break off his visit after a week; the two men never met again but they corresponded much over the years until Wilhelm’s death and several people travelled between Hven and Kassel over the years reporting on the latest developments and achievements.
Tycho returned to Copenhagen in 1575 now determined to devote his life to astronomical research, leaving Denmark if necessary to set up in Basel or some other suitable European metropolis. Frederick II was very impressed with the tasks that he had commissioned Tycho to fulfil in his name and decided it was time to bind the obviously talented young aristocrat to his court. He praised Tycho and offered him an attractive range of different stewardships and fiefs. All of those on offer would have required Tycho to engage political or militarily or both in Danish life and that is exactly what he didn’t want so he demurred, asking for time to consider.
It came to Frederick’s ears that Tycho was planning on leaving Denmark for Basel, for example. In the meantime Wilhelm of Kassel, whose sister was married to Frederick’s uncle, had sent an emissary to Copenhagen recommending that his cousin fulfil Tycho’s desires and help him to found an observatory in Denmark. Whether on his own initiative, or prompted by Tycho’s uncle Steen Billie, Frederick now offered Tycho the island of Hven, which lies between Denmark and Sweden as his fief with a yearly stipend generous enough to build and operate what would become the greatest observatory in Europe.
Tycho is credited in the popular history of astronomy with three major achievements: he is given credit for destroying the Aristotelian cosmological claims that the heavens are perfectand unchanging, the planet orbit on crystalline spheres and that comets are sublunar meteorological phenomena through his observations of the 1572 supernova and the 1577 comet. His major contributions were, of course, his more that twenty year long systematic astronomical observations and records that laid the foundations for the astronomy of the seventeenth century. Lastly he is given credit for the geo-heliocentric system, that bears his name, an important intermediate stage on the way to the acceptance of a heliocentric system.
Whilst the observational catalogue can be attributed to Tycho and his numerous employees alone and he is justifiably acknowledged as the second most important figure in sixteenth century astronomy, after Copernicus, as far as the other two achievements are concerned their sole attribution to Tycho is not justified and in fact produce a distortion in the historical record.
As I pointed out in Part I the Aristotelian theory of comets had already begun to be questioned by Toscanelli, Peuerbach and Regiomontanus in the fifteenth century. As I explained in Part V, in the 1530s comets had again become a major topic of investigation and discussion under Europe’s leading astronomers. By the 1570s all the astronomers in Europe eagerly observed the supernova from 1572 and the comet from 1577 and Tycho was only one of several important astronomers, who recognised that these were supralunar phenomena and reported them as such. Michael Mästlin and Thaddaeus Hagecius ab Hayek both established and respected astronomers certainly had more influence on the acceptance of these new discoveries than Tycho in the 1570s. Really crucial for this important step towards a new cosmology was the acceptance by Christoph Clavius, professor of mathematics at the Collegio Romano, and as such the most influential Ptolemaic astronomer in Europe.
This very brief sketch shows that the dismantling of these aspects of Aristotelian cosmology was the result of numerous astronomers observing, discussing and offering new theories of nearly two centuries and not the heroic act of a single astronomer. The end of celestial perfection and the destruction of Aristotle’s crystalline spheres was an important stage in the emergence of modern astronomer but it is not one that should be credited to Tycho alone.