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As time passed and the end of the 16th century approached, Copernicus’s solutions and techniques and Copernican tables began to seem more and more convincing and indispensable to successive generations of mathematicians and astronomers, and each generation was less wedded than the last to Ptolemaic assumptions. Owen Gingerich, with whom we began this
chapter
, has made it a sleuthing project to track down existing early editions of
De revolutionibus
, to catalogue them and to see what scholars of the 16th century (in the tradition of ‘glossing’ that still survived from the Middle Ages) penned in the margins. He has discovered that marginal comments, clarifications and criticisms were passed from teacher to pupil, sometimes for several generations, branching out family-tree fashion. Gingerich tells us in his book
The Great Copernicus Chase
, ‘These second-hand annotations reveal that even if Copernicus’s revolutionary new doctrine failed to find a place in the regular university curriculum, a network of astronomy professors scrutinized the text and their protégés carefully copied out their remarks, setting the notes on to the margins of fresh copies of the book with a precision impossible by aural transmission alone.’ Undoubtedly Copernicus’s ideas were spreading and having an increasing impact. It appeared as though Copernican astronomy were headed for a peaceful victory, and scripture could and would be reinterpreted to agree with a new vision of the universe.

In the ancient Hellenistic world, Aristarchus’s proposal had failed to overturn Earth-centred astronomy. What was different now that made the change more acceptable? First, while Aristarchus had simply raised the suggestion that the Sun, not the Earth, lay at the centre of the universe, Copernicus gave his readers a good deal of mathematics to chew on, mathematics that they found interesting and useful even if they didn’t follow Copernicus all the way. Also, there was strong support from observational astronomy coming along early in the next century – new data that Ptolemaic astronomy of that era had difficulty explaining, and Copernican astronomy explained with ease.

But to understand more fully why an idea that was ignored in the ancient world should finally make its impact 17 centuries later, it’s necessary to look beyond astronomy and mathematics and notice that the 16th and early 17th centuries in Europe were an era of intense intellectual, religious, political and
cultural
ferment. There was a mounting spirit of upheaval and distrust of old assumptions, across the board. Anti-Aristotelianism and humanism were challenging and infiltrating scientific thought with Neoplatonic preferences for geometric and mathematical harmony and simplicity that Ptolemaic astronomy could not provide. Luther and Calvin and their followers, and Henry VIII as well, were calling into question the ultimate ancient authority of the Roman Catholic Church, offering, in its place, not one authority and doctrine but a rich and confusing choice. The Catholic Church was also of many minds on many fronts, so that it is misleading to speak of ‘the Church’ as though it were a monolith, holding one opinion. The great age of exploration was underway. Columbus had sailed for the New World when Copernicus was in his late teens. Ptolemy’s ancient maps were proving to be inaccurate. Was there perhaps reason to distrust his astronomy as well? Ancient copies of Ptolemy’s work had turned up and made it impossible to sustain the hope that problems with his astronomy stemmed only from Arabic misinterpretation that could be corrected if scholars knew what Ptolemy had actually said himself. This was a world in many ways ready to entertain the exhilarating thought that with Copernicus humankind had finally not only caught up with, but surpassed, the thinking of the ancients and was ready to move onward, unintimidated by the past.

Nicolaus Copernicus didn’t single-handedly overturn the Earth-centred view that had prevailed since ancient times. But he did push open the door that would lead us towards our modern understanding of the universe. This time, the door wouldn’t be closed again. As Hoyle puts it, ‘It is because Copernicus focused the attention of the world at precisely the right spot, the place where Nature simply had to give up her secrets, that today we judge his work to have been so important.’ Hoyle uses a mountaineering term: Copernicus discovered the ‘point of attack’. Others would soon be gearing up to make the climb.

CHAPTER 3

Dressing Up the Naked Eye

1564–1642

I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use.

Galileo Galilei

IT WOULD BE
difficult to imagine two educated men of the same historical period more different from one another in background and personality than Johannes Kepler and Galileo Galilei. Kepler was a quiet, introspective man from Weil der Stadt, Württemberg, on the outskirts of the Black Forest near Stuttgart. Galileo was a colourful, feisty, larger-than-life character who hailed from Florence and Pisa when these were world-class centres of wealth, political power and artistic and intellectual ferment.

Kepler’s family history was respectable – his grandfather had been a burgomaster – but his father was an evil-tempered ne’er-do-well who abandoned his family; and Kepler’s mother was a quarrelsome troublemaker who dabbled in the occult and barely escaped burning as a witch. Galileo’s father was a well-educated trader, with a reputation in Florentine intellectual circles as an accomplished musician and music theorist.

Kepler was an unassuming, private man who didn’t win friends easily, who struggled for a living teaching, which he didn’t do particularly well, and casting horoscopes, which he reputedly did very well indeed, meanwhile pursuing his real passions: mathematics, astronomy and philosophy. Galileo won both friends and enemies readily, relished the spotlight and lived a public, even celebrity life. He thought highly of himself, and he had a flair for self-promotion and an astounding talent as a writer for conveying his scientific ideas to non-expert readers, including some in high places whose favour he curried.

Kepler was a devout Protestant; Galileo a staunch Catholic.

But far more significant than any of these differences was the contrast between the ways in which the two men approached their science. Kepler had a mind that moved by leaps of fancy and intuition and a Neoplatonic Christian faith that the universe, created by God, must have a beautiful hidden harmony to it – that things as far apart as music and geometry and cosmology must have connections, must fall into place and explain one another. Though Galileo made mistakes – insisting, for instance, that the tides were powerful evidence of the correctness of Copernican theory – it is the bulk of Kepler’s work that appears to modern eyes much wider of the mark. His most celebrated discoveries seem like small islands of dazzling insight in a sea of wild, woolly thinking. In fact, much of what Kepler wrote appears completely crazy, until we recall that his greatest contributions to our understanding of the universe were at first equally much flights of intuition and imagination, and equally motivated by his longing to uncover hidden harmony, symmetry and relationships. It took a mind that could think as ‘far out’ as Kepler and follow as many false leads as he did – and then proceed to pin ideas down with conscientious mathematical rigour – to discover connections that really do exist. Galileo, on the other hand, started from what he observed, whether that was a swinging chandelier in the church at Pisa or tiny stars parading around the planet Jupiter. He had a
firm
belief that the only way to learn the truth about nature was to examine it directly and put it to the test. Though eager and able to speculate about the implications of his discoveries, he was reluctant to espouse publicly or even among friends any ideas for which he didn’t see clear support from his own experiments or observations.

For all their genius, each of these men was also remarkably favoured by happenstance. Each had fall into his hands something without which his most celebrated discoveries would never have been made. For Kepler that was the naked-eye astronomical observations of the great Danish astronomer Tycho Brahe; for Galileo, the telescope.

Together, Kepler and Galileo were responsible for the triumph of Copernican astronomy, yet they never met.

Johannes Kepler was born in 1571, 28 years after the death of Copernicus and the publication of
De revolutionibus
. His boyhood in Weil der Stadt, with his unpleasant mother and, occasionally, his irresponsible father – in a household full of other unsavoury, unhappy relatives – was as dreadful as anything ever dreamt of by Charles Dickens. The young Kepler was seldom in good health and a childhood illness left him with weak eyesight. Nevertheless, it became clear early on that he had extraordinary intellectual gifts and a deeply religious nature, neither of which endeared him to his schoolmates. He wasn’t good at making friends.

Kepler hoped to become a Lutheran minister, and he went on from the local school to a theological academy for the children of ‘poor and pious people’ (Kepler’s family met the first requirement, if not the second) and then to the university at Tübingen, where scholarships paid his way. The Senate of the University observed that Kepler had ‘such a superior and magnificent mind that something special may be expected of him’. Tübingen still taught Ptolemaic astronomy, but it was during this period that Kepler became a Copernican, perhaps
due
to the influence of the private views of the astronomer Michael Mästlin, who was one of his teachers. For an example of what astronomy was like before telescopes: Mästlin’s study of the nova of 1572, using no instrument at all except for a piece of thread, gave results more accurate than anyone else’s, including Tycho Brahe.

In 1594, when Kepler was 23 and in his final year as a theology student, a teaching job in mathematics and astronomy opened up at a seminary in Graz, Austria. The University of Tübingen nominated Kepler. Though surprised and somewhat distressed at this sudden change in his career trajectory, Kepler accepted the position.

Kepler wasn’t a good teacher, but his new job evidently did leave him time to pursue his science and philosophy, for only two years after he began teaching he published the first book since
De revolutionibus
to defend Copernican theory, and he made a far stronger case for it than Copernicus had been able to do. The 24-word title of Kepler’s book is usually shortened to
Mysterium
or, translated,
Cosmographic Mystery. Mysterium
is a book that elicits, at best, tolerant smiles from modern readers, in spite of its support of Copernicus and the ingenious nature of its proposal. Kepler attempted to explain both the number of planets and the sizes of their orbits in terms of a relationship between the planetary spheres and the five regular solids of geometry: cube, tetrahedron, dodecahedron, icosahedron and octahedron.
See Figure 3.1.

The publication of
Mysterium
led to the first known contact between Kepler and Galileo. At Padua, where he was teaching at the time, Galileo received a copy of Kepler’s book. He wrote to Kepler saying he was looking forward to reading it and also that he had long believed in the Copernican theory himself but had not said so openly, to avoid ridicule. In a return letter, Kepler urged Galileo to make his opinion public. Galileo didn’t take that advice.

Kepler continued eking out a living in Graz as an ineffective
teacher
, went on with his astronomical work, wrote some books about astrology, and married – a marriage that lasted, though there is some indication it was not an entirely happy one. Then in 1598, the Archduke Ferdinand began to make life miserable for Lutheran leaders and teachers. Things went from bad to worse and, eventually, given a day’s notice to leave Graz
altogether
or be sentenced to death, Kepler departed. It soon became evident that the Archduke’s attitude was intransigent. Kepler would no longer be able to live and work in Graz.

Figure 3.1

(a) The five regular or ‘cosmic’ solids. In every case, all of the sides are identical and only equilateral figures are used for them. These are the only possible regular or ‘cosmic’ solids.