Category Archives: History of Astronomy

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

Before continuing with Tycho Brahe’s contributions to the development of modern astronomy It pays to take stock of the existing situation in the last quarter of the sixteenth century. The Middle Ages had cobbled together a model of the cosmos that consisted of three separate but interlocking blocks: Aristotelian cosmology, Ptolemaic astronomy and Aristotelian physics, whereby it should be noted that the medieval Aristotelian physics was, to paraphrase Edward Grant, not Aristotle’s physics. In order for a new astronomy to come into use, as we shall see, the whole model had to dissembled and each of the three blocks replaced with something new.

As we saw at the beginning, some aspects of Aristotelian cosmology–supralunar perfection and cometary theory–were already under scrutiny well before Copernicus published his De revolutionibus. They now fell following the European wide observations of the supernova in 1572 and the great comet of 1577; the Aristotelian crystalline spheres went with them, although Clavius, the leading Ptolemaic astronomer of the age, whilst prepared to sacrifice supralunar perfection and Aristotelian cometary theory was not yet prepared to abandon the crystalline spheres. The model was beginning to crumble at the edges.

The acceptance of Copernicus’ heliocentric system had been very meagre but the interest in his mathematical models, his astronomical data and the planetary tables and ephemerides based on them had originally been very great. However, it quickly became clear that they were no more accurate or reliable than those delivered by the Ptolemaic system and the initial interest and enthusiasm gave way to disappointment and frustration. Out of this situation both Wilhelm IV in Kassel and Tycho Brahe in Denmark, following Regiomontanus’ initiative from a century earlier, decided that what was needed was to go back to basics and produce new star catalogues and planetary tables based on new accurate observations and set about doing just that. We have already looked to Wilhelm’s efforts; we now turn to Tycho’s.

Granted the island of Hven and the necessary financial support to carry out his project by Frederick II, the Danish king, Tycho set to work.


Frederick II of Denmark Portrait by Hans Knieper or Melchior Lorck, 1581.

Whereas it is theoretically possible to question the claim that Wilhelm IV had built an observatory no such doubt exists in Tycho’s case. What he erected on his island was not so much an observatory, as a research institute the like of which had never existed before in Europe,

The centrepiece of Tycho’s establishment was his palace Uraniborg, a magnificent purpose built red brick residence and observatory. The structure included a large mural quadrant and outer towers on the balconies of which a large array of self designed and constructed instruments were situated.


Source: Wikimedia Commons


Engraving of the mural quadrant from Brahe’s book Astronomiae instauratae mechanica (1598) Source: WIkimedia Commons

As it turned out that the accuracy of the tower-mounted instrument was affected by vibration caused by the wind, so Tycho constructed a second observatory, Stjerneborg. This observatory was effectively situated underground in a large pit to reduce wind vibration of the instruments.


Drawing of an above ground view of Stjerneborg Willem Blaeu – Johan Blaeu, Atlas Major, Amsterdam, 1662 Source: Wikimedia Commons


Schematic of Stjerneborg showing underground chambers: Woodcut from F.R. Friis “Tyge Brahe”, Copenhagen, 1871 Source: Wikimedia Commons

As well as his two state of the art observatories, Tycho also constructed alchemical laboratories in the cellars of Uraniborg, to carry out experiments in Paracelsian pharmacology. To publish the results of his researches Tycho constructed his own printing press and to ensure that he would have enough paper for those publications, he also constructed a water powered paper mill.

Whereas Wilhelm’s astronomical activities were a side project to his main occupation of ruling Hesse-Kassel and the work on his star catalogue was carried out by just two people, Rothmann and Bürgi, Tycho’s activities on Hven were totally dedicated to astronomy and he employed a small army of servants and assistants. Alongside the servants he needed to run his palace and its extensive gardens Tycho employed printers and papermakers and a large number of astronomical observers. Some of those who worked as astronomers on Hven and later in Prague, such as Longomontanus, who later became professor for astronomy in Copenhagen, did so for many years. Others came to work for him for shorter period, six or nine months or a year. These shorter-term periods working for Tycho worked like a form of postgrad internship for those thus employed. Good examples of this are the Dutch cartographer and Globemaker Willem Janszoon Blaeu (1571–1638) spent six months on Hven in 1595-96


Willem Janszoon Blaeu Source: Wikimedia Commons

and the Franconian mathematician and astronomer Simon Marius (1573–1625) who spent six months in Tycho’s observatory in Prague in 1601 shorty before Tycho’s death.

Tycho’s observation programme was massive and very much for the duration, starting in the mid 1570s and continuing up to his death in 1601[1]. His teams spent every night of the year, weather permitting, systematically observing the heavens. Two teams, one in Uraniborg and the other in Stjerneborg, made the same observations parallel to but completely independent of each other, allowing Tycho to compare the data for errors. They not only, over the years, compiled a star catalogue of over 700 stars[2]with an accuracy of several factors higher than anything produced earlier but also systematically tracked the orbits of the planets producing the data that would later proved so crucial for Johannes Kepler’s work.

When Tycho was satisfied with the determination of the position of a given star then it was engraved on a large celestial globe that he had had constructed in German on one of his journeys. When Willem Janszoon Blaeu was on Hven, Tycho allowed him to make a copy of this globe with the new more accurate stellar positions, which he took with him when he returned to The Netherlands. So from the very beginning Blaeu’s commercial celestial spheres, which dominated the market in the seventeenth century, were based on the best astronomical data available.

Tycho not only systematically observed using instruments and methods known up to his times but devoted much time, effort and experimentation to producing ever better observing instruments with improved scales for more accurate readings. He also studied and developed methods for recognising and correcting observational errors. It is not an exaggeration to say that Tycho dedicated his life to producing observational astronomical data on a level and of a quality never before known in European astronomy.

In 1588 Tycho’s patron and benefactor Frederick II died and after a period of regency his son, who was only eleven years old when he died, was crowned king as Christian IV in 1596.


Portrait Christian IV by Pieter Isaacsz 1612 Source: Wikimedia Commons

Due to a mixture of court intrigue and his own arrogance, Tycho fell into disfavour and Christian cut off his finances from the crown. Still a wealthy man, from his private inheritances, Tycho packed up his home and some of his instruments and left Denmark heading south through Germany in 1597, looking for a new patron. In 1599 he settled in Prague under the patronage of Rudolf II as Imperial Mathematicus,


Rudolf II Portrait by Martino Rota Source: Wikimedia Commons

erecting a new observatory in a castle in Benátky nad Jizerou about fifty kilometres from Prague.


Benátky Castle Source: Wikimedia Commons

Tycho’s biggest problem was that he had vast quantities of, for the time, highly accurate astronomical data that now needed to be processed and he was in desperate need of a mathematician who was capable of carrying out the work. Fate intervened in the form of the still relatively young Johannes Kepler ((1571–1630), who turned up in Prague in 1600 frantically looking for employment.


Johannes Kepler Source: Wikimedia Commons

This was a partnership made in hell rather than heaven but it did not last long as Tycho died under unclear circumstances[3]in October 1601, with Kepler inheriting his position as Imperial Mathematicus. I will deal with Kepler’s leading role in the story of modern astronomy in later episodes but we still need to look at Tycho’s last contribution, the so-called Tychonic system.

[1]In his Bibliographical Directory of Tycho Brahe’s Artisans, Assistants, Clients, Students, Coworkers and Other Famuli and Associatespages 251–309 in his On Tycho’s Island: Tycho Brahe, Science, and Culture in the Sixteenth Century, John Robert Christianson list 96 names.

[2]When he left Hven Tycho increased his star catalogue to 1000, taking the missing stars from the Ptolemaic star catalogue

[3]Anybody who brings up, in the comments, the harebrained theory that Kepler murdered Tycho in order to obtain his astronomical data will not only get banned from the Renaissance Mathematicus in perpetuity but will be cursed by demons, who will visit them in their sleep every night for the rest of their pathetic lives

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

Kepler was wot, you don’t say?


The Guardian is making a serious bid for the year’s worst piece of #histsci reporting or as Adam Shapiro (@tryingbiology) once put it so expressively, #histsigh! The article in question has the shock, horror, sensation headline: Groundbreaking astronomer Kepler ‘may have practised alchemy’. Ignoring the fact for the moment that he probably didn’t, given the period and the milieu in which Kepler lived and worked saying that he may have been an alchemist is about as sensational as saying he may have been a human being.


Johannes Kepler Source: Wikimedia Commons

The period in which Kepler lived was one in which the interest in alchemy was very widespread, very strong and very open. For eleven years he was Imperial Mathematicus at the court in Prague of the German Emperor Rudolph II, which was a major centre for all of the so-called occult sciences and in particular alchemy. In Prague Kepler’s original employer Tycho Brahe had been for years a practitioner of Paracelsian alchemical medicine (a very widespread form of medicine at the time), which to be fair the article sort of says. What they say is that Tycho was an alchemist, without pointing out that his alchemy was restricted to medical alchemy.


Tycho Brahe Source: Wikimedia Commons

One of his colleagues was the Swiss clockmaker Jost Bürgi, who had come to Prague from Hesse-Kassel,


Jost Bürge Source: Wikimedia Commons

where the Landgrave Moritz was a major supporter of alchemy, who appointed Johannes Hartmann (1568–1631) to the first ever chair for chemistry, actually Paracelsian medicine, at the university of Marburg. The real surprise is not that Kepler was an alchemist or practiced alchemy but rather that given the time and milieu in which he lived and worked that he wasn’t and didn’t.


Johannes Hartmann Source: Wikimedia Commons

How can I be so sure that Kepler didn’t dabble in alchemy? Simply because if he had, he would have written about it. Kepler is a delight, or a nightmare, for the historian, there is almost no figure that I know of in #histSTM, who was as communicative as Kepler. He wrote and published eighty three books and pamphlets in his lifetime covering a very wide range of topics and in all his written work he was always keen to explain in great detail to his readers just what he was doing and his thoughts on what he was doing. He wrote extensively and very openly on his mathematics, his astronomy, his astrology, his family, his private affairs, his financial problems and all of his hopes and fears. If Kepler had in anyway been engaged with alchemy, he would have written about it. If anybody should chime in now with, yes but alchemists kept they activities secret, I would point out in Kepler’s time the people practicing alchemy, particularly the Paracelsians, were anything but secretive. And it was with the Paracelsians that Kepler had the closest contact.

There are a few letters exchanged between Kepler and his Paracelsian physician friends, which show quite clearly that although Kepler displayed the natural curiosity of a scientific researcher in their alchemistic activities he did not accept the basic principles of alchemy. In his notorious exchange with Robert Fludd, he is very dismissive of Fludd’s alchemical activities. Kepler was not an alchemist.

From a historical point of view particularly bad is the contrast deliberately set up in the article between good science, astronomy and mathematics, and ‘dirty’ pseudo- science’, alchemy. This starts with the title:

Groundbreaking astronomer Kepler ‘may have practised alchemy’

Continues with the whole of the first paragraph:

The pioneering astronomer Johannes Kepler may have had his eyes on the heavens, but chemical analysis of his manuscripts suggests he was “willing to get his hands dirty” and may have dabbled in alchemy.

“Kepler, who died in 1630, drew on Copernicus’s work to find laws of planetary motion that paved the way for Isaac Newton’s theory of gravity” is contrasted with “The authors speculate that Kepler could have learned the “pseudo-chemical science.” 

A ‘pioneering astronomer’ with ‘his eyes on the heavens’, serious scientific activity, but ‘dabbled in alchemy’. Whoever wrote these lines obviously knows nothing about Kepler’s astronomical writing nor about early 17thcentury alchemy.

The article through its choice of descriptive terms tries to set up a black/white dichotomy between the man who paved the way for modern astronomy, good, and the practitioners of alchemy in the early seventeenth century, bad. However if we actually look at the real history everything dissolves into shades of grey.

Kepler was not just an astronomer and mathematician but also a practicing astrologer. People might rush in here with lots of Kepler quotes condemning and ridiculing the nativity horoscope astrology of his age, all of them true. However, he famously said one shouldn’t throw the baby out with the bath water defending the basic idea of astrology and presenting his own unique system of astrology based entirely on aspects, that is the angular position of the planets relative to each other. The author of the piece has obviously never turned the pages of either Kepler’s Mysterium Cosmographicum or his Harmonice Mundi. As I commented on Twitter, during a discussion of this article, Kepler’s cosmological heuristic with which he generated all of his successful astronomy was, viewed from a modern rational standpoint, quite simply bat shit insane. Things are not looking good for our pioneering astronomer.


Kepler’s Platonic solid model of the solar system, from Mysterium Cosmographicum (1596) Kepler’s explanation as to why there are only five planets and their order around the sun! Source: Wikimedia Commons

On the other side, as I have noted on several occasions, alchemy included much that we now label applied and industrial chemistry.  For example, alchemists were responsible for the production of pigments for painters and gunpowder for fireworks and cannons, and were often glassmakers. Alchemists were historically responsible for developing the laboratory equipment and methodology for chemical analysis. In the period under discussion many alchemists, including Tycho, were Paracelsian physicians, who are credited with the founding of the modern pharmacological industry. Historians of alchemy tend to refer to the alchemy of the seventeenth century as chymistry because it represents the historical transition from alchemy to chemistry. Not so much a pseudo-science as a proto-science.

Let us now consider the so-called evidence for the articles principle claim. Throughout the article it is stated that the evidence was found on Kepler’s manuscripts, plural. But when the evidence is actually discussed it turns out to be a single manuscript about the moon. On this manuscript the researchers found:

“…very significant amounts of metals associated with the practice including gold, silver, mercury and lead on the pages of Kepler’s manuscript about the moon, catalogued as “Hipparchus” after the classical astronomer.”

Is alchemy the only possible/plausible explanation for the traces of metals found on this manuscript? Could one suggest another possibility? All of these metals could have been and would have been used by a clock and instrument maker such as Jost Bürgi, who was Kepler’s close colleague and friend throughout his eleven years in Prague. Bürgi also had a strong interest in astronomy and might well have borrowed an astronomical manuscript. Of course such a solution doesn’t make for a sensational article, although all the available evidence very strongly suggests that Kepler was not an alchemist.

One final point that very much worries me is the provenance of this document. It is four hundred years old, who has owned it in the meantime? Where has it been stored? Who has had access to it? Until all of these questions can be accurately answered attributing its contamination to Kepler is just unfounded speculation.










Filed under History of Alchemy, History of Astrology, History of Astronomy, History of science, Myths of Science, Renaissance Science

Everything you wanted to know about Simon Marius and were too afraid to ask – now in English

Regular readers of this blog should by now be well aware of the fact that I belong to the Simon Marius Society a small group of scholars mostly from the area around Nürnberg, who dedicate some of their time and energy to re-establishing the reputation of the Franconian mathematicus Simon Marius (1573–1625), who infamously discovered the four largest moons of Jupiter literally one day later than Galileo Galilei and got accused of plagiarism for his troubles. Galileo may have discovered them first but Marius won, in the long term, the battle to name them.


Frontispiece of Mundus Iovialis Source:Wikimedia Commons

In 2014 the Simon Marius Society organised many activities to celebrate the four-hundredth anniversary of the publication of his opus magnum, Mundus Jovialis (The World of Jupiter). Amongst other things was an international conference held in Nürnberg, which covered all aspects of Marius’ life and work. The papers from this conference were published in German in 2016: Simon Marius und seine Forschung (Acta Historica Astronomiae), (AVA, Leipzig).


Now after much effort and some delays the expanded translation, now includes the full English text of Mundus Jovialis, has become available in English: Simon Marius and his Research, Springer, New York, 2019.


The ebook is already available and the hardback version will become available on 19 August. I apologize for the horrendous price but the problem of pricing by academic publishers is sadly well known. Having copyedited the entire volume, which means I have read the entire contents very carefully I can assure you that there is lots of good stuff to read not only about Simon Marius but also about astronomy, astrology, mathematics, court life in the seventeenth century and other topics of historical interest. If you can’t afford a copy yourself try to persuade you institutional library to buy one! If your university library buys a copy from Springer then students can order, through the library, a somewhat cheaper black and white copy of the book.


Filed under History of Astrology, History of Astronomy, History of Mathematics, Renaissance Science

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

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.


Tycho Brahe Source: Wikimedia Commons

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.


Peder Oxe Source: Wikimedia Commons

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 IV Source: Wikimedia Commons

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.


Frederick II of Denmark Portrait by Hans Knieper or Melchior Lorck, 1581.

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.


The Great comet of 1577, seen over Prague on November 12. Engraving made by Jiri Daschitzky. Source: Wikimedia Commons

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.


Star map of the constellation Cassiopeia showing the position (labelled I) of the supernova of 1572; from Tycho Brahe’s De nova stella Source: Wikimedia Commons

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.






Filed under History of Astronomy, Renaissance Science

The Copernican Revolution 101

This is a review of a book that is intended to deliver what the post title implies, Todd Timberlake and Paul Wallace, Finding Our Place in the Solar System: The Scientific Story of the Copernican Revolution (CUP, 2019).


The book was developed as a textbook for a course–Astronomy 120: The Copernican Revolution–which Todd Timberlake teaches as a science requirement for students majoring in non-scientific fields at Berry College in Georgia (USA). The course was originally taught by Paul Wallace and when he left Berry College, Todd Timberlake, an astronomer and physicist, took over the course using Wallace’s teaching material, hence the double authorship. It will come as no surprise that I very much support the idea of introducing students to science through its history, as is done here. Timberlake is an astronomer and not a historian so the emphasis is very much on the scientific content and less on the context in which it developed but he includes potted biographies of the main figures involved.

After a brief introduction on the nature of science and the evolution of scientific knowledge, which is well done, Timberlake moves on in the next three sections of the book to explaining how the ancient picture of the cosmos developed introducing all of the astronomical terminology as he progresses. This is excellently done but I do have one minor objection. In basic astronomy there is a lot of terminology that is not part of everyday language, to start with there are three different coordinate systems for locating objects in the heavens. I have read numerous accounts of all this over the years and I still sometimes get confused and I find a glossary of the technical terms very useful for a quick check, this book doesn’t have one.

What the book does have is at the end of each section a short chapter titled Reflections on science, a sort of philosophy of science light. Having actually studied philosophy of science with some first class teachers I was prepared to be highly sceptical of these but they are actually very well done and add, in my opinion, a lot to the value of the book as a teaching text.

The next sections of the book, each of which consists of five or six short chapters, deal successively with Copernicus, Tycho Brahe, Kepler, Galileo and Newton. Mainlining the mainstream figures, which despite my own love of the minor and oft unheralded contributors, is OK for what is intended as an introductory text. I was particularly impressed with his sensitive and sympathetic treatment of Kepler’s, quite frankly, totally bizarre cosmological heuristic. The tenth and final section of the book is titled, Confirming Copernicus: evidence for Earth’s motion, which takes the reader in quick short steps down to the nineteenth century. The book closes with twenty short appendices that present to mathematics of the various historical developments, which had been largely left out of the main texts.

The book has extensive endnotes that are mostly references to the equally extensive and comprehensive bibliography. There is also a detailed and extensive index.

Timberlake writes well and lucidly. His text is easy to read and his explanations are clear and straightforward. He covers the material well and I on the whole would thoroughly endorse his book as an excellent textbook and introduction to the history of European astronomy.

There are several minor historical errors in the potted biographies that I shall leave without comment, as to do so would make this review appear more negative than it should. However there is one major historical falsehood that I simply cannot and will not ignore. Having delivered a good account of ancient Geek astronomy Timberlake has a section titled, Astronomy and cosmology after Ptolemy. The third sentence of this section reads as follows:

The rise of Christianity in Europe led to the neglect of mathematical astronomy, and of the “pagan” knowledge of the ancient Greeks and Romans generally. At the same time astronomy flourished in the Arabic world. Many Greek astronomical and philosophical works, including the Almagest and Planetary Hypotheses, were translated into Arabic. (p. 96)

This is of course the classic ‘Christianity killed ancient science’ myth, which in the year 2019 should not be part of a college level historical textbook. Let us examine the facts one more time. Classical Greek learning began to decline in the ancient world from the middle of the second century CE due to a general socio-political and cultural decline, which had absolutely nothing to do with the rise of Christianity. It had basically disappeared in the Western Empire (Europe) by the end of the fifth century CE. The only places, within the Western Empire where it survived, was within the Christian monasteries, which preserved a modicum of the classical learning. The late encyclopaedists such as Boethius and Isidore, who rescued what could still be rescued, were Christians. The Islamic Empire did not begin to appropriate Greek knowledge until the eighth century CE. Their first sources of Greek scientific and philosophical works were those that had been translated into Syriac by Nestorian Christians, within the Persian Empire. Their second, and major, source was Byzantium, the Eastern Empire, which was Christian. By the eighth century there began the first low level returns of Greek astronomical knowledge into Europe during the Carolingian Renaissance in the form of calendrical and computus studies. Christianity didn’t neglect Greek astronomy it played a leading role in conserving and transmitting it during a period of general cultural collapse[1].

A second historical howler, that I can’t ignore, is not as important as his propagation of the classic Christianity killed ancient science myth and in fact I’m not sure whether it should make me laugh or cry. He points out correctly that the heliocentric system establishes a relative measure of the planetary orbits based on the average distance between the Earth and the Sun, the Astronomical Unit of AU. (p.126) To this he adds the following footnote:

Copernicus did not in fact, use the Astronomical Unit in this way, but modern astronomers do. Copernicus typically assigned some large number (say 10,000) of undefined units to the Earth-Sun distance and then found the radii of the planetary orbits in terms of these units. He used a large number in order to avoid having to deal with fractions –or decimals, which did not come into common use until after the French Revolution. [my emphasis]

Decimals were known and used both in Chinese and Arabic mathematics before they entered Europe. The first European author to introduce decimals was Simon Stevin in his De Thiende published in Dutch in 1585 and translated into French as Disme and English as Decimal Arithmetic. Stevin’s system of decimals did not use the decimal point, which was introduced by Christoph Clavius or by Bartholomaeus Piticus in his trigonometrical tables. Decimals were in common use throughout the seventeenth century particularly in both trigonometrical and logarithmic tables. I can only surmise that Timberlake is confusing decimals with the metric system.

As already stated above, Timberlake’s book is an excellent entry level introduction to the history of European mathematical astronomy as well as serving as an introduction to the process of science for non scientists and anybody looking to teach themselves or looking for a textbook for an advanced school class or a college level course should definitely consider using this volume and at an official retail price of just £29.99 for an excellent produced hardback it should be well within the buying power of the average student.


[1]For details read Stephen C. McCluskey, Astronomies and Culture in Early Medieval Europe, CUP, ppb. 2000 and Dimitri Gutas, Greek Thought, Arabic Culture: The Graeco-Arabic Translation Movement in Baghdad and Early ‘Abbāsid Society (2nd–4th/8th–10thcenturies), Routledge, ppb. 1998.


Filed under Book Reviews, History of Astronomy, Renaissance Science

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

In the initial phase of its reception the thing that most interested the readers of De revolutionibus were the planetary tables and ephemerides that Copernicus’ new mathematical models delivered. There was great enthusiasm for this aspect of his work in the hope that it would deliver more accurate celestial data for cartography, navigation and astrology the principle reasons why people, during this period, were interested in astronomy. It was not long before that initial enthusiasm began to wain, as people realised that although they were different inaccuracies the new sets of table were as error strewn and inaccurate as the old ones based on the works of Ptolemaeus. The problem was that the tables produced from De revolutionibus were based on the same star catalogue, the one in Ptolemaeus’ Mathēmatikē Syntaxis. This star catalogue had over the years become very corrupted through errors that crept in by repeated manuscript copying and recalculating the values for new locations.

We can find this very clearly expressed by the English mathematicus Thomas Harriot (c. 1560–1621) a true polymath, who produced significant scientific discoveries in cartography, navigation, mathematics, astronomy, chemistry, physics and linguistics.


Portrait often claimed to be Thomas Harriot (1602), which hangs in Trinity College, Oxford. Source: Wikimedia Commons

He was also one of those early Copernican, who accepted Copernicus’ cosmology. Unfortunately Harriot’s only publication was a brief account of his voyage to North America With Walter Raleigh (c. 1552–1618) in 1585–86, where he became viewed historically North America’s first scientist, so all of his scientific advances had little or no impact. In chapter 3 of an unpublished navigation manual that he wrote for the captains of Raleigh’s fleet he discussed taking the declination of the sun. He says sailors used two different methods. The Spanish and Portuguese sailors used one based on the Alfonsine tables derived from Ptolemaeus in 1252 but first published in the 15thcentury and the other based on the theory of certayne notable mathematicians & especially of one Nicolaus Copernicus of Cracow in poland. He writes that the Alfonsine tables lead to obvious errors in the determination of latitudes.

The latter were Reinhold’s Prutenic Tables and Harriot say that declination tables were usually made from Stadius’ Ephemerides; he adds these should be better tables but:

it falleth out they are worse; our owne men find faults, as also the Spaniardes but know not where the fault is, nether is it to be tried, found, or decerned by there manner of experiments.

He goes on the explain that the work of Tycho Brahe (1546-1601) at Huaena (Hven) and the Landgrave of Hesse had shown that: ‘Copernicus his tables; the prutenickes, & all ephimerides made out of them’ were half a degree or more out of the sun’s place, and the Alfonsine about a quarter of a degree. Although living withdrawn from society on the outskirts of London Harriot was well aware that both Tycho Brahe and the Landgrave of Hesse knew of the inaccuracies in the tables based on De revolutionibus and as we shall see undertook programmes to correct the problem; aiming to fulfil the aims of Regiomontanus when he moved to Nürnberg about a hundred years earlier.

Harriot’s Landgrave of Hesse was actually Wilhelm IV, Landgrave of Hesse-Kassel (1532–1592).


Wilhelm IV Source: Wikimedia Commons

He was born the eldest son of Philipp I, Landgrave of Hesse (1504–1567) (known as Philip the Magnanimous) and his first wife Christine of Saxony (1505–1549). Philip was one of the earliest Lutheran Protestant rulers in Germany and founded the Protestant University of Marburg in 1527. Wilhelm was introduced to astronomy by his mathematics teacher Rumold Mercator (1541–1599), the son of Gerhard Mercator, in the form of Peter Apian’s Astronomicum Caesareum (1540). Wilhelm was fascinated by the volvelle in Apian’s masterwork, rotating paper calculators used to determine the position of celestial object. In 1559/1560 together with Andreas Schöner (1528-1590), the son of the Nürnberger mathematicus Johannes Schöner (1477-1547), Wilhelm conceived the idea of designing and constructing a clock that would display all the celestial movements given by the volvelle in Apian’s book. This mechanical masterpiece was to be crowned with a celestial globe giving the position of all of the principle fixed stars.


The so-called Wilhelmsuhr or planet clock

On comparing the star tables in both Ptolemaeus and Copernicus with his own actual observations Wilhelm realised that both star catalogues were woefully inaccurate. This would lead him to his programme of re-determining the position of all of the fixed stars.

The earliest recorded observation that we have made by Wilhelm and Andreas Schöner dates from 1558 but most of the records of his early astronomical activities were lost during WWII. Wilhelm is credited with having established the first European observatory but this claim is very dependent on how you define observatory. All of his instruments, which were designed and constructed by the clockmaker Eberhard Baldewein (c. 1525–1593), who was also responsible for the construction of the celestial clock together with the clockmaker Hans Bucher and the case-maker Hermann Diepel, were portable instruments. These were stored in a room in his palace


The Landgrave’s palace in Kassel on an old postcard based on a painting from about 1800 Source: Wikimedia Commons

from where they were carried out onto a balcony to make observations.


Sternwarte im Astronomisch-Physikalischen Kabinett, Foto: MHK, Arno Hensmanns Reconstruction of Wilhelm’s observatory

Wilhelm’s early astronomical activities were supported by Andreas Schöner and Victorinus Schönfeldt (1525–1592), a graduate of Wittenberg, who on Philipp Melanchthon’s recommendation became professor for mathematics on the University of Marburg in 1557, as well as various unnamed assistants. Due to the pressure of his work as heir and then following the death of his father as landgrave his programme to re-determining the position of all of the fixed stars didn’t get started until the 1580s.

In 1578 Wilhelm appointed the twenty-seven year old Swiss clock and instrument maker Jost Bürgi (1552–1632) as clock maker to his court to replace Hans Bucher, who had been Eberhard Baldewein assistant, and who had died in 1578.


Bürgi was a very inventive clock maker and probably the best at his craft living in Europe at the time. Although he was very famous in his lifetime it is not known where or when and from whom he learnt the craft of clock making. In 1584 Wilhelm added the astronomer Christoph Rothman to his staff. Rothmann is a frustrating figure for the astronomy historian. Even by the normal level paucity of knowledge about Renaissance scientific figures, our knowledge about the life of Rothmann, an important figure in the reception of Copernican heliocentrism, is almost non-existent. His date of birth is not known but estimated to be between 1550 and 1560 and it is assumed that he was born in Bernburg, Saxony-Anhalt because later in life he signed himself Mathematicus Christophorus Rothmannus Bernburgensis when he matriculated at the University of Wittenberg in 1575, where he studied theology and mathematics.

Between 1584 and 1589 Rothmann and Bürgi, with the active support of Wilhelm, produced a catalogue containing the newly determined positions of 387 stars, determined to a, for the time, very high level of accuracy. Unfortunately this catalogue first saw the light of day in 1618, as the Hesse-Kassel astronomical team disintegrated starting in 1590. In 1590 Rothmann was sent off on a journey to Hven by Wilhelm to study the instruments and methodology of Tycho Brahe. He never returned from that journey although still under contract to Wilhelm in Kassel. Why he went AWOL is simply not known. It is known that he returned to Bernburg, where he seems to have abandoned astronomy, writing instead theology tracts that he never published. His date of death is not known but was probably around 1600 but not later than 1608. In 1592 Wilhelm presented his nephew Rudolph II, the German Emperor, with one of Bürgi’s mechanical globes and Bürgi was sent to Prague with the globe to demonstrate it to Rudolph. Not long after Bürgi moved into the Emperor’s employment in Prague, as during his absence Wilhelm had died. Wilhelm’s son Moritz (1572–1632), like his father an academic, turned his attention from the study of astronomy to the study of alchemy, the court in Kassel becoming an important centre for alchemy along with the Marburg University, which from this period claims the oldest chair for chemistry, in reality a chair for Paracelsian alchemical medicine.

Although Wilhelm’s efforts to produce a new reliable star catalogue rather fizzled out, he played a major roll in inspiring and promoting another parallel effort to do the same, that of the Danish aristocrat Tycho Brahe.



Filed under History of Astronomy, Renaissance Science

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

Although highly anticipated the expectation placed upon De revolutionibus and the reactions to it were highly diverse and covered a very wide spectrum from complete acceptance to total rejection with many variation in between. It would be impossible in a blog post series such as this one to deal with the multitude of single reactions that would require a fairly substantial book; in fact I have two such books sitting next to my computer at the moment–Pietro Daniel Omodeo, Copernicus in the Cultural Debates of the Renaissance: Reception, Legacy, Transformation (Brill, 2014) & Jerzy Dobrzycki ed., The Reception of Copernicus’ Heliocentric Theory (D Reidel, 1972)–which I recommend to anybody who wants an in depth, blow by blow account. What I intend to do here is sketch the basic trends of that reception.

Famously Robert Westman once claimed that only ten people in the whole world accepted Copernicus’ heliocentric hypothesis, including his cosmology, completely between its publication in 1553 and the year 1600. His list actually misses a couple of total accepters such as Gemma Frisius, who acknowledged his acceptance in his foreword to Johannes Stadius’ ephemerides, and the Englishman John Feild who made the same acknowledgement in his ephemerides. However, it does include three others who either dropped or appeared to drop their acceptance. Christoph Rothmann (born between 1550 & 1560 died probably after 1600) one of Wilhelm IV’s astronomers (of which more later), who had an extensive dispute with Tycho Brahe, who of course didn’t accept Copernicus’ cosmology, on the subject and in the end, and according to Tycho was converted to his point of view.  Diego de Zúñiga (1536–1597), a Spanish Augustinian hermit and academic, who wrote a defence of the heliocentric hypothesis in his In Job commentaria (1584) but later in life rejected Copernicus’ hypothesis as incompatible with Aristotelian philosophy, probably under religious pressure from his superiors. The most peculiar renegade was Copernicus’ first and initially strongest supporter, Rheticus. Having gone quiet on Copernicus and his hypothesis for some time after he moved to Kraków, in a correspondence with Pierre de la Ramée (1515-1572) he announced that he had erected a large gnomon in Kraków and was now practicing the true astronomy of the Egyptians, whatever that might be. Summa summarum, one can say without much contradiction that there were never more than about fifteen, and probably less, true Copernican in the world before 1600 or even before 1609/10 when the publications of Kepler and the invention of the telescope became game changers.

There were a few astronomers, who simply rejected Copernicus’ hypothesis without comment and some, who simply ignored it but they won’t interest us here because the evidence shows that the vast majority did react to it in some way or another. As already mentioned earlier Owen Gingerich carried out a survey of all known surviving copies of the 1st(Nürnberg 1543) and 2nd(Basel 1566) editions of De revolutionibus[1]and his analysis of the annotation and marginalia of the readers clearly shows that the majority took very little notice of the first cosmological part of the book but concentrated their reading instead on the technical parts of the book, the mathematical models and the data.

This rejection of the heliocentric aspect of Copernicus’ work was a simple and direct consequence of the fact that he could not provide any empirical evidence to support his claims that the Earth revolved on its own axis and that it orbited a stationary Sun. Both claims very clearly contradicted the evidence of one’s own senses, we still say the Sun rises and sets, and suggested consequences that Copernicus was unable to answer. If the Earth is rotating at approximately 1600 kilometres an hour at the equator, why doesn’t everything on the surface get blown off by the headwind? And if the Earth is orbiting the Sun, why can’t we detect stellar parallax? These are just two of the possible objections to which Copernicus could not provide scientific answers.

The answers, based on assumptions, which he did propose would prove with time and new developments in science to be fundamentally correct but at the time there were merely unsubstantiated assumptions. In answer to the first he suggested that everything on the Earth’s surface would be carried along with it in some sort of envelope. This turned out to be correct but Copernicus lacked the physics necessary to explain how this would function. In fact the history of physics of the seventeenth century, as we shall see, consisted to a large extent of developing the knowledge to provide this explanation. As far as stellar parallax was concerned, or rather the lack of it, Copernicus simply and correctly assumed that the stars were simply too far away for the parallax to be detected with the naked-eye. However, Copernicus and almost all of his contemporaries still believed in the sphere of the fixed stars and if this sphere was so far away that stellar parallax was undetectable then the distance between the orbit of Saturn and the sphere of the fixed stars would have to be inconceivably vast and thus not very acceptable. Simply put, why all of that empty space out there?

The ambivalence towards Copernicus magnum opus is nicely illustrated by the Welsh mathematicus Robert Recorde (c. 1512–1558) in his The Castle of Knowledge (1556) the first English text to refer to the Copernican hypothesis. On the subject of the possible motion of the Earth he wrote:

             But as for the quietness of the earth, I need not to spend any time in proving of it, since that opinion is so firmly fixed in most men’s heads, that they accompt it mere madness to bring the question in doubt. And therefore it is as much folly to travail to prove that which no man denieth, as it were with great study to dissuade that thing which no man doth covet, neither any man allow: or to blame that which no man praiseth, neither any man liketh.

Scholar: Yet sometimes it chanceth, that the opinion most generally received, is not most true

Master: And so do some man judge of this matter, for not only Eraclides [Heraclides] Ponticus, a great Philosopher, and two great clerks of Pythagoas school, Philolaus and Ecphantus, were of the contrary opinion, but also Nicias [Hicetas] Syracusius, and Aristarchus Samius, seem with strong arguments to approve it: but the reasons are too difficult for this first Introduction, and therefore I will omit them till another time. And so I will do the reasons that Ptolemy, Theon and others do allege, to prove the earth to be without motion: and the rather, because those reasons do not proceed so demonstrably, but they may be answered fully, of him that holds the contrary. I mean, concerning circular motion: marry, direct motion out of the centre of the world seemeth more easy to be confuted, and that by the same reasons, which were before alleged for proving the earth to be in the middle and centre of the world.

Scholar: I perceive it well: for as if the earth were always out of the centre of the world, those former absurdities would at all times appear: so if at any time the earth should move out of his place, those inconveniences would then appear.

Master: That is truly to be gathered: how be it, Copernicus, a man of great learning, of much experience, and of wonderful diligence in observation, hath renewed the opinion of Aristarchus Samius, and affirmeth that the earth not only moveth circularly about its centre, but also may be, yea and is, continually out of the precise centre of the world 38 hundred thousand miles: but because the understanding of that controversy dependeth of profounder knowledge than in this Introduction may be uttered conveniently, I will let it pass till some other time.

Scholar: Nay sir in good faith, I desire not to hear such vain fantasies, so far against common reason, and repugnant to the consent of all the multitude of Writers, and therefore let it pass for ever, and a day longer.

Master: You are too young to be a good judge in so great a matter: it passeth for your learning, and theirs also that are much better learned than you to improve [i.e. disprove] his supposition by good arguments, and therefore you were best to condemn nothing that you do not well understand but another time, as I said, I will so declare his supposition, that you shall not only wonder to hear it, but also peradventure be as earnest then to credit it, as you are now to condemn it.


In this exchange Recorde appears to both reject and praise Copernicus’ hypothesis. Unfortunately we will never know his true opinion as he died before he could write the advanced text that he promises his readers here. What, however, is very clear is that Recorde is very well informed about the history of both diurnal rotation and the heliocentric hypothesis.

Some of the readers, who only considered the mathematical parts of the book, simply took Copernicus’ models for the various planets and applied them to a geocentric system, hoping thereby to produce a better predictive model for the position of the planets. Other took this remodelling a step further and using Copernicus’ mathematical models revived the Capellan model, well-known and much loved in the Middle Ages; a geocentric system in which Mercury and Venus orbit the Sun, which in turn orbits the Earth.


Naboth’s representation of Martianus Capella’s geo-heliocentric astronomical model (1573) Source: Wikimedia Commons

Others took this thought one step further and developed, what is now known the Tychonic system, named after Tycho Brahe (1546–1601), although he was by no means the first or the only astronomer to publish this system in the second half of the sixteenth century, all claiming to have developed it independently. In this helio-geocentric system all of the planets except the Moon, orbit the Sun, which together with the Moon orbits the stationary Earth. Heliocentric, geocentric and helio-centric model based on Copernicus’ parameters and mathematical model can and have been shown to be mathematically equivalent with nothing to recommend one over the other, without further information.


The Tychonic System Source: Wikimedia Commons

One interesting but slightly confusing development was that some geocentric and helio-geocentric astronomers accepted the arguments for the Earth spinning on its own axis, diurnal rotation, whilst still rejecting the Earth orbiting the Sun. As I wrote here in an earlier blog post, this idea goes back at least to Heraclides Ponticus (c.390 BCE–c.310 BCE) and was adopted or discussed and rejected many times over the centuries down to Copernicus’ times. The argument in its favour is a purely physical one. It is much simpler for the comparatively small Earth to rotate than for the vastly larger and heavier sphere of the fixed stars. This acceptance of diurnal rotation would prove to be an important steeping stone to the complete acceptance of the heliocentric model in the seventeenth century.

On major group, who showed great interest in Copernicus’ mathematics and above all in the planetary tables and ephemerides that they delivered were the astrologers. This basically means all professional and half professional astronomers, as they were almost all practicing astrologers. As stated above Robert Westman once claimed that there were only ten Copernicans in the whole world between 1543 and 1600, a historian of astrology correctly pointed out that all ten were practicing astrologers. Like Regiomontanus in the previous century (see Part II of this series) they all thought that more accurate astronomical data would improve the quality of their astronomical prognoses. Not only did they avidly consult the ephemerides of Stadius and Feild but several of them such as the Italian mathematicus Giovanni Antonio Magini (1555–1617) unsatisfied with Stadius’ and Feild’s accuracy also calculated their own new ephemerides. In the end, however, the astrologers recognised that although the errors in Copernican tables were different to those in Ptolemaic ones they were not much more accurate as we will see in the next instalment.

[1]Owen Gingerich, An Annotated Census of Copernicus’ De Revolutionibus(Nuremberg, 1543 and Basel, 1566), Brill, Leiden, Boston, Köln, 2002


Filed under History of Astronomy, Renaissance Science, Uncategorized