Category Archives: History of Astronomy

Polluting Youtube once again!

Professor Christopher M Graney, Renaissance Mathematicus friend and guest blogger, has posted another of his holiday videos on Youtube, documenting parts of his visit to Nürnberg and Bamberg for the Astronomy in Franconia Conferences. In his new video “Nürnberg and Bamberg” you can see the Behaim Globe (Martin Behaim celebrates his 555th birthday today!), the Frauenkirche Clock (1509) doing its thing, and yours truly wittering on about Johannes Petreius and Copernicus’ De revolutionibus (4.11–6.56)

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Filed under Early Scientific Publishing, History of Astronomy, History of science, Renaissance Science

The horror, the horror!

For those readers who might have wondered what The Renaissance Mathematicus looks and sounds like, you need wonder no more. There is now a video on Youtube in which I stumble and stutter my way through a very impromptu, not quite fifteen minute, lecture on the relationship between astronomy, astrology and medicine in the Early Modern Period. During which I indulge in a lot of arm waving and from time to time scratch my fleas. This video was filmed in the kitchen of the Remeis Observatory in Bamberg during a coffee break at the Astronomy in Franconia Conference last Monday, complete with the sounds of somebody loading the dishwasher.

The cameraman, who also puts some questions during this solo performance, was Chris Graney who requested my golden words for his students back in Louisville, the poor sods.

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Filed under Autobiographical, History of Astrology, History of Astronomy, History of medicine

Jesuit Day

Adam Richter (@AdamDRichter) of the Wallifaction Blog (he researches John Wallis) tells me that the Society of Jesus, known colloquially as the Jesuits, was officially recognised by Pope Paul III on 27th September 1540. He gives a short list of Jesuits who have contributed to the history of science over the centuries. Since this blog started I have attempted to draw my readers attention to those contributions by profiling individual Jesuits and their contributions and also on occasions defending them against their largely ignorant critics. I have decided to use this anniversary to feature those posts once again for those who came later to this blog and might not have discovered them yet.

My very first substantive post on this blog was about Christoph Clavius the Jesuit professor of mathematics at the Collegio Romano, the Jesuit university in Rome, who as an educational reformer introduced the mathematical sciences into the curricula of Catholic schools and universities in the Early Modern Period. I wrote about Clavius then because I was holding a lecture on him at The Remeis Observatory in Bamberg, his hometown, as part of the International Year of Astronomy. I shall be holding another lecture on Clavius in Nürnberg at the Nicolaus Copernicus Planetarium at 7:00 pm on 12 November 2014 as part of the “GestHirne über Franken – Leitfossilien fränkischer Astronomie“ series. If you’re in the area you’re welcome to come along and throw peanuts.

I wrote a more general rant on the Jesuits’ contributions to science in response to some ignorant Jesuit bashing from prominent philosopher and gnu atheist A. C. Grayling, which also links to a guest post I wrote on Evolving Thoughts criticising an earlier Grayling attack on them. This post also has a sequel.

One of Clavius’ star pupils was Matteo Ricci who I featured in this post.

A prominent Jesuit astronomer, later in the seventeenth-century, was Riccioli who put the names on the moon. I have also blogged about Chris Graney’s translation of Riccioli’s 126 arguments pro and contra heliocentricity. Chris, a friend and guest blogger on the Renaissance Mathematicus, has got a book coming out next year on The University of Notre Dame Press entitled Setting Aside All Authority: Giovanni Battista Riccioli and the Science against Copernicus in the Age of Galileo. It’s going to be a good one, so look out for it.

Riccioli’s partner in crime was another Jesuit, Francesco Maria Grimaldi, who features in this post on Refraction, refrangibility, diffraction or inflexion.

At the end of the seventeenth-century the Jesuit mathematician, Giovanni Girolamo Saccheri, without quite realising what he had achieved, came very close to discovering non-Euclidian geometry.

In the eighteenth-century a towering figure of European science was the Croatian Jesuit polymath, Ruđer Josip Bošković.

This is by no means all of the prominent Jesuit scientists in the Early Modern Period and I shall no doubt return to one or other of them in future posts.




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

Another one bites the dust

This is a sort of footnote to my last post in which I criticised science writer Tim Radford for propagating myths about the reception of heliocentricity in the sixteenth-century. Now a second truly legendary astronomer and science writer, John Gribbin, has turned up in the comments and shown that he also lives in the nineteenth-century, as far as history of science is concerned, when John William Draper and Andrew Dickson White created the myth of an eternal war between science and religion and presented Giordano Bruno and Galileo Galilei, alongside lesser lights such as Michael Servetus and Marco-Antonio de Dominis, as the scientific victims of Christian persecution.

Rushing in where angels fear to tread Gribbin sought to defend Radford’s honour with the following comment:

As a card-carrying pedant, I would point out that Tim says “ideas like that”, not “that idea”. Which makes Bruno relevant, whether you like it or not.

Now I appreciate Mr Gribbin’s attempt to help his friend and colleague but in doing so he has only displayed his own ignorance of the material. There was a very good reason why I ended my last post with the following tongue in cheek warning:

P.S. If anybody mentions either Giordano Bruno or Galileo Galilei in the comments I will personally hunt them down and beat them to death with a rolled up copy of The Guardian.

No modern historian of science, knowledgeable of the history of astronomy in the Early Modern Period, would follow Draper and White in viewing Bruno as a martyr of science. This is a myth that has been thoroughly debunked and which is, these days, usually only dug up by historically ignorant gnu atheists and others of that ilk, as a weapon with which to beat the Catholic Church around the head. As John Gribbin has walked straight into the trap we will just briefly examine why the Church committed Giordano Bruno to the flames.

A Dominican monk, Bruno came under suspicion of heresy and fled his Southern Italian monastery in 1576. He spent the next sixteen years wandering around Europe blowing his own trumpet, generally annoying people and pissing off the authorities, both civil and religious, wherever he went. Returning to Italy he landed, not unsurprisingly in the clutches of the Roman Inquisition. He was held prisoner and interrogated for seven years before being tried for heresy, found guilty, and executed by burning at the stake in 1600. The proceedings of his trial have disappeared so it is not known what exactly he was found guilty of but summary was discovered in 1940 and a list of the charges against him is known:

  • holding opinions contrary to the Catholic faith and speaking against it and its ministers;
  • holding opinions contrary to the Catholic faith about the Trinity, divinity of Christ and Incarnation;
  • holding opinions contrary to the Catholic faith pertaining to Jesus as Christ;
  • holding opinions contrary to the Catholic faith regarding the virginity of Mary, mother of Jesus;
  • holding opinions contrary to the Catholic faith about both Transubstantiation and Mass;
  • claiming the existence of a plurality of worlds and their eternity;
  • believing in metempsychosis and in the transmigration of the human soul into brutes;
  • dealing in magics and divination.

Now this list is not hidden away somewhere, I just borrowed it from the Wikipedia Bruno article, so Mr Gribbin could have consulted it himself. He would of course pounce on the sixth item on the list gleefully crying I told you so, but let us examine if he should be so sure of being right.

Given the fact that Bruno was accused of breaching almost every single central doctrine of the Catholic Church did this one point of highly speculative cosmology really play such a central role in his conviction and subsequent execution, I hardly think so. In fact I don’t think it played much of a role at all compared to his denying the divinity of Christ and the virgin birth. However there is more.

Bruno’s claiming the existence of a plurality of worlds and their eternity has little or nothing to do with Copernicus’ heliocentric theory the original statement for which Tim Radford claimed one could be condemned to the stake. Copernicus proposed a finite sun centred cosmos, Bruno speculated about an infinite universe filled with homogenously distributed infinite sun each with their own populated planets and no centre. The two proposals don’t have an awful lot in common. Copernicus expressly refused to enter the discussion as to whether the cosmos was finite or infinite, and never speculated about other inhabited planets. He, as a good Catholic cleric, would definitely have rejected an eternal universe as this contradicted the Creation. What about the two leading Copernican of Bruno’s own times? Kepler explicitly rejected Bruno’s infinite universe and infinite suns and in doing so brought the earliest known argument against Olbers’ paradox. Galileo simply ignored him. I think it is safe to say that the cosmological statements that were included in Bruno’s indictment were not ideas like Copernicus’ heliocentric theory, as claimed by Gribbin.

Gribbin’s claim also suffers from another problem. The reason why Bruno’s cosmological speculations were included in his indictment was very clearly theological and not scientific. As already mentioned if, as Bruno claimed, the universe were eternal then there could be no Creation, highly heretical. In fact this was one of the central reasons why the Catholic Church rejected the Greek philosophy of Atomism. Secondly if there were infinite populated worlds there would be serious problems with the doctrine of salvation through Jesus. If he was the only Son of God did he visit all of the infinite populated planets, simultaneously, one after the other? Or were there infinite Jesuses? Did he only save the earth? Then what about the other planets? A really tangled mess for the Catholic theologians! As with Galileo in 1615 if Bruno had had anything remotely like proof for his cosmology he might have had something he could argue with but he didn’t, all he had was pure unscientific, unsubstantiated speculation. As I sated in earlier posts Bruno’s cosmological speculations were anything but scientific and anything but accurate. As far as we know the universe is finite and not infinite, it had a starting point and will almost certainly have an end. There are neither infinite stars (suns) nor infinite planets and those that there are, are not distributed homogenously. To stylise Bruno as a scientific martyr, as Draper/White did in the nineteenth-century and as John Gribbin apparently still wants to do, boarders on the grotesque.







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

I expected better of Tim Radford

Tim Radford is a science writer who works for The Guardian newspaper. In fact many people consider him the best British science writer of the current crop, not without a certain amount of justification. Because of this I was, as a historian of science, more than disappointed by the opening paragraph of his latest post on the science section of the Guardian’s website, a book review: “The Copernicus Complex by Caleb Scharf review – a cosmic quest”. Radford opens his review with three sentences of which the third caused me to groan inwardly and bang my head in resignation on my computer keyboard.

The Copernican principle changed everything. It was not formulated by Copernicus, who in 1543 proposed only that the Earth was not the centre of the universe, and that the motion of the Earth around the sun could explain the irregularities in the heavens. At the time, ideas like that could get people condemned to the stake. [my emphasis]

I ask myself how much longer historians of science are going to have to keep repeating that this statement is complete and utter rubbish before science writers like Tim Radford finally take their hands off their ears and the blinkers from their eyes and actually accept that it is wrong. No Mr Radford, an astronomer or cosmologist in the sixteenth-century suggesting that we live in a heliocentric cosmos rather than a geocentric one was not in danger of being condemned to the stake and yes there is solid historical evidence, which apparently you choose to ignore in favour of your fantasies, to prove this. Let us briefly review that evidence for those, like Tim Radford, who have obviously not been paying attention.

Already in the fifteenth- century Nicholas Cusanus openly discussed various aspects of the heliocentric hypothesis in his works, presenting them in a favourable light. Was he condemned to the stake for his audacity? No he was treated as an honoured Church scholar and appointed cardinal.

Let us move on to the subject of Radford’s highly inaccurate statement, Copernicus, like Cusanus a cleric and a member of the Church establishment, how did the Church react to his provocative heliocentric claims? In 1533 the papal secretary, Johann Albrecht Widmannstetter held a lecture on Copernicus’ theories to Pope Clemens VII and assembled company in the papal gardens. We assume this was based on Copernicus’ Commentariolus, the manuscript pamphlet of his ideas written around 1510, as De revolutionibus wasn’t published until 1543. Was he condemned to the stake for his rashness? No, Clemens found much favour in his lecture and awarded him a valuable present for his troubles. Two years later Widmannstetter became secretary to Cardinal Nikolaus von Schönberg, an archbishop and papal legate, who had been present at that lecture. In 1536 Schönberg wrote a letter to Copernicus urging him to make his theories public and even offering to pay the costs of having his manuscript copied. Not a lot of condemning to the stake going on there. Copernicus had Schönberg’s letter printed in the front of De revolutionibus.

Dear Tim Radford I am sure that as a topflight science writer you check the scientific facts in the articles that you write very carefully to ensure that you are not misleading your many readers. May I humbly request that in future you pay the same attention to the historical facts that you publish so as not to serve up your readers with pure unadulterated historical hogwash?

P.S. If anybody mentions either Giordano Bruno or Galileo Galilei in the comments I will personally hunt them down and beat them to death with a rolled up copy of The Guardian.




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

Galileo, Foscarini, The Catholic Church, and heliocentricity in 1615 Part 2 –the consequences: A Rough Guide.

In part one I outlined the clash, which took place between Galileo and Foscarini on the one side and the Catholic Church on the other in the second decade of the seventeenth-century. I ended by saying that this initial confrontation had very few consequences for Galileo at the time, who continued to be the highly feted darling of the North Italian in-crowd, including the higher echelons of the Catholic Church. Of course the events of 1615/16 would come back to haunt Galileo when he was tried for writing and publishing his Dialogo in the 1630s but that is a very complex topic that require a post of its own sometime in the future. I also wrote that the books of Foscarini and of the Protestant Copernicans, Michael Maestlin and Johannes Kepler were placed on the Index of Forbidden Books. Interestingly De revolutionibus was only placed on the Index until corrected. It is here that we will pick up the thread and examine the consequences of the Church’s actions on the development of astronomy in the seventeenth-century.

What did it mean when I say that De revolutionibus was only placed on the Index until corrected? This means that De revolutionibus was not forbidden but that only those statements within the book, which claimed that heliocentricity was a proven fact, were to be removed. This mild censorship, only a handful of passages in the whole book were affected, was carried out comparatively quickly and the thus censored version was given free to be used by astronomers already in 1621. The whole of this episode demonstrates that the powers that be within the Church were well aware that De revolutionibus was an important astronomical text and should, despite the judgement of the eleven members of the commission set up to adjudicate on the affair that the idea that the Sun is stationary is “foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture…”; while the Earth’s movement “receives the same judgement in philosophy and … in regard to theological truth it is at least erroneous in faith”, remain available to Catholic astronomers for their studies.

There is a widespread popular perception that the Church’s theological rejection of the theory of heliocentricity led to a breakdown of astronomical research in Catholic countries in the seventeenth-century. Nothing could be further from the truth. As mentioned in the first part of this post, some historians think that Cardinal Bellarmino’s admission in his letter to Foscarini that … if there were a real proof that the Sun is in the centre of the universe, that the Earth is in the third sphere, and that the Sun does not go round the Earth but the Earth round the Sun, then we should have to proceed with great circumspection in explaining passages of Scripture which appear to teach the contrary …, was interpreted by many Jesuit and Jesuit educated astronomers as a challenge to find an empirical proof for heliocentricity. As we shall see there is quite a lot of circumstantial evidence to support this claim.

An important historical fact to be born in mind when considering the development of astronomy in the seventeenth-century was that there existed no empirical proof for the heliocentric hypothesis, whether it be in the original form proposed by Copernicus or the much more sophisticated form developed by Kepler. The astronomers would have to wait until 1725 before James Bradley delivered the first proof of the earth’s annual orbit around the sun with his discovery of stellar aberration and slightly longer before the geodesists demonstrated that the earth is an oblate spheroid thus confirming a prediction made by both Newton and Huygens that diurnal rotation would result in the earth having this form thus proving indirectly the existence of diurnal rotation. This tends to be forgotten or simply ignored by those claiming that the Church should have accepted heliocentricity as a fact in 1615. In reality the heliocentricity became accepted by almost all astronomers whether Catholic or non-Catholic by around 1660, long before any empirical proof existed, on the basis of accumulated circumstantial evidence and the lack of a convincing alternative. A lot of that circumstantial evidence was delivered by Catholic astronomers, who despites the Catholic theological position, continued to work avidly on the development of the modern astronomy.

It is also important to realise that although the Church banned claiming that heliocentricity was a fact, the heliocentric theory, it was still perfectly possible to speculate about heliocentricity, the heliocentric hypothesis. Throughout the seventeenth-century Catholic astronomers in Italy adopted an interesting strategy to deal with the Church’s ban of the heliocentric theory. They would preface their works with a statement of the fact that in its wisdom the Church had shown the heliocentric theory to be contrary to Holy Scripture and thus factually false and then proceed to discuss this interesting mathematical hypothesis without claiming it to be true. This strategy sufficed for the Inquisition’s guardians of the truth and thus the astronomers continued to discuss and disseminate heliocentricity with impunity.

Scientific theories are not only disseminated by their supporters but often also by their opponents. Long before Galileo muddy the waters with his heated challenge to the Church’s exclusive right to interpret the Bible it is certain that more people learnt of the existence of the heliocentric hypothesis and its basic details from the works of Christoph Clavius, a convinced defender of geocentricity, than from De revolutionibus. In his commentary on the Sphere of Sacrobosco, an introductory astronomy textbook, Clavius discussed Copernicus’ heliocentric hypothesis sympathetically, respecting its mathematical sophistication, whilst firmly rejecting it. This book went through numerous editions and was the most widely disseminated and read, by both Catholic and Protestant students, astronomy textbook throughout most of the seventeenth-century and was for many their first introduction to the ideas of Copernicus. It was also Clavius’ postgraduate students, in his institute for mathematical research at the Collegio Romano, who provided the very necessary empirical confirmation of Galileo’s telescopic discoveries in 1611, shortly before Clavius’ death. This activity by Jesuit astronomers pushing the boundaries of astronomical knowledge did not cease following the decisions of 1616.

There was a slowdown in the development of modern astronomy in the second and third decades of the seventeenth-century that has nothing to do with the Church’s ban but was the result of a lack of technological advance. In the four years between 1609 and 1613 European astronomers had discovered everything that it was possible to discover using a Dutch or Galilean telescope with a convex objective and a concave eyepiece. The only new discoveries were the observations of a transit of Mercury by Gassendi in 1631 and a transit of Venus by Horrocks in 1639 neither of which had an immediate impact because they didn’t become widely known until much later. For various reasons, not least Galileo’s very public rejection of it as inferior, the superior Keplerian or astronomical telescope, with two convex lenses, didn’t start to become established until the 1640s. However once established the new discoveries began to flow again: the moons of Saturn, the rings of Saturn, diurnal rotation of the planets. Many of these new discoveries, which added new circumstantial evidence for heliocentricity, were made by Giovanni Domenico (Jean-Dominique) Cassini (1625–1712) a Jesuit educated Catholic astronomer. It was also Cassini, with the support of his teachers the Jesuits Giovanni Battista Riccioli and Francesco Maria Grimaldi, who proved, using the heliometer constructed for this purpose in the San Petronio church in Bologna, that either the sun’s orbit around the earth or the earth’s orbit around the sun must be an ellipse, as required by Kepler. Although this proved that the orbit is an ellipse it didn’t show which system was correct.

Cassini, who would go on to become the leading observational astronomer in Europe, always avoided committing himself to any systems simply delivering empirical results and leaving the cosmological interpretation to others. Although confirming Cassini’s heliometer results Riccioli stayed committed to semi-Tychonic system, in which the inner planets orbited the Sun, which in turn together with Saturn and Jupiter orbited the Earth. Riccioli presented this rather bizarre mongrel in his Almagestum Novum published in 1651. Riccioli’s Almagestum contained descriptions of all the various possible systems, including the Copernican, and became a very widely disseminated and read technical textbook for astronomers, both Catholic and Protestant. Like Clavius before him, Riccioli introduced many to heliocentricity for the first time. The Almagestum contained 126 arguments concerning the Earth’s motion 49 pro and 77 contra the most extensive discussion of the problem ever. You can read Chris Graney’s English translation of the arguments here. Although Riccioli came out against heliocentricity his analysis was sympathetic enough to the concept that he was actually investigated by the Inquisition.

Having been made available by the Index copies of De revolutionibus appear only to have been actually censored within Italy nearly all the surviving censored copies, including Galileo’s, coming from there. Outside of Italy, with the notable exception of Descartes, nobody seems to have taken very much notice of the Inquisition’s ban. Descartes appears to have withheld publication of his The World, in the 1630s, containing his defence of heliocentricity, out of respect for his Jesuit teachers. Publishing his views, in modified form, first in his Principles of Philosophy in 1644.

Another Frenchman, Pierre Gassendi like Descartes educated by the Jesuits, who became professor of mathematics at the Collège Royal in Paris in 1645 published his views on astronomy in his Institutio astronomica, although formally a supporter of the Tychonic system, Gassendi’s presentation of the Copernican system is so sympathetic that many historians have interpreted him as a secret supporter of heliocentricity. Gassendi also published biographies of Tycho, Peuerbach, Regiomontanus and Copernicus. Like Riccioli, Gassendi’s astronomical writings were very popular and very widely read, again leading to a widespread dissemination of the principles of heliocentricity.

Another leading French Catholic astronomer, Ismael Boulliau was an open and avid supporter of the Keplerian elliptical astronomy and was indeed the first to hypothesise that gravity ought to be an inverse quadrate force, a significant step in the road to acceptance of heliocentricity. It was Boulliau’s dispute with the English astronomer Seth Ward about Kepler’s second law, which nobody liked, both parties offering alternatives, that first made Newton aware of Kepler’s system.

By about 1660 enough circumstantial evidence had been accumulated that most astronomers in Europe both Catholic and Protestant, with the necessary education to do so, had accepted heliocentricity as a fact with a small minority still holding out for a Tychonic system. In the end the Tychonic system had fallen victim of Ockham’s razor being viewed as overly complex in comparison with the Keplerian elliptical system for which more and more evidence had accumulated throughout the preceding fifty years. A significant advance in the development of modern physics in which Galileo’s Discorsi had played an important role also contributed crucially to this acceptance, dealing as it did with the physical problems of terrestrial motion. A detailed analysis of these developments would make this already over long post even longer and must be dealt with separately.

Although by no means an exhaustive presentation of the development of astronomy in the seventeenth-century, I think the above contains enough to demonstrate that the Church’s ban of the heliocentric theory had very little negative influence on that development and that Catholic astronomers played a leading role within it. Returning to my earlier speculation, I feel justified in saying that had Galileo and Foscarini not forced the Church’s theologians into a corner in 1615, then the Catholic astronomers, and in particular the Jesuits and their pupils, would have led the Church to an acceptance of heliocentricity within the seventeenth-century.




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

“…realigning the heavens with a single stroke of the brush.“ – Really?

Recently on twitter I stumbled across a problematic discussion, as to which single image had most changed the course of science. Although the various participants made stimulating and interesting suggestions, Darwin’s tree diagram, Franklin’s photo of DNA etc. I found this discussion problematic because it suffers from the same difficulties as discussion in the history of science as “the first”, “the greatest”, “the father of” and all similar hyperbolic claims, just how do you measure and compare the numerous candidates that spring to mind?

This discussion didn’t just appear out of cyberspace on somebody’s whim but was provoked by Joe Hanson at It’s OK to be Smart and his post Message from the Moon, which in turn was provoked by the set of washes of the moon by Galileo that had been circulating on Twitter a couple of days before.

Galileo's washes of the moon.

The watercolour sketches that Galileo made of his initial telescopic observations of the moon in 1609/10 are iconic images in the history of science that did have a major impact on the way humanity viewed the cosmos but there are an awful lot of inaccuracies in Hanson’s description of that impact that I am going to analyse here.

Hanson’s first minor error is to claim that the images he has posted on his blog are included in the Sidereus Nuncius. Galileo’s legendary publication does indeed included woodcuts of five of his lunar watercolours but the sheet displayed by Hanson, and here above, was not included, a trivial but important point.

Hanson informs us:

But hiding in their shadows lies a greater significance. The squiggled edges of that bleeding ink bear an observation that altered the heavens themselves. Or at the very least, our view of them.

And then goes on to explain why:

In 1610, cosmology, not that it had much to show for itself as a science, was still based on the ideas of Aristotle, who by this time had been dead for 18 centuries. So current! Copernicus’ observation that the Earth orbited the sun, first published in 1543, had begun to challenge Aristotelian supremacy, it wasn’t exactly a popular idea. 

Aristotle’s cosmological beliefs were based on the idea that the heavens were made of a perfect substance called “aether”, and therefore the circular motions and spherical shapes of heavenly bodies were also perfect. Earth, he claimed, was inherently imperfect, as were all the things that existed upon it. Everything in the heavens was awesome, and Earthly matter was inherently “just okay”, even if its name was Aristotle. This was one of the reasons people found Copernicus’ claims so hard to swallow. The imperfect Earth among the perfect heavens? Heresy! [emphasis in original]

Somewhat sloppily expressed but so far so good, although placing the earth in the heavens didn’t really play that much of a role in the initial rejection of Copernican cosmology being insignificant in comparison to the physical problems engendered by a moving earth. Hanson’s argument is that because Galileo’s interpretations of what he saw through his telescope, and don’t forget that they are interpretations, clearly suggested that the moon was not smooth and perfect but had a landscape like the earth he had realigned “the heavens with a single stroke of the brush”; a nice literary figure of speech but unfortunately one that doesn’t fit the historical facts.

Already in antiquity people, had speculated that the differing shades of the moons surface were the result of a mountainous landscape. This viewpoint was expressed most notably by Plutarch in his On The Face Which Appears in the Orb of the Moon, one of his collection of essays, the Moralia. This was well known and widely read in the sixteenth-century and was even used by Kepler as a springboard for his own “lunar geography”, the Somnium, written but not published before Galileo made his telescopic discoveries. This widespread alternative concept of the lunar surface made it much easier to accept Galileo’s discovery and considerably weakened any impact that it might have had on Aristotelian cosmology. However this was not the only factor that gives the lie to Hanson’s “single stroke of the brush” postulate. Aristotle’s division of the cosmos into two spheres one superlunar, which was perfect, unchanging and eternal, everything below, and the other sublunar, which was imperfect, constantly changing and subject to decay had been under attack for most of the century preceding Galileo’s discoveries, as I have already outlined in my post on Comets and Heliocentricity.

In the 1530s observations of several comets had led many leading European astronomers to the conclusion that comets were superlunar phenomena and not sublunar ones as Aristotle’s cosmology required. Comets are of course anything but perfect, unchanging and eternal. In the 1570s another generation of European astronomers, Tycho Brahe and Michael Maestlin to the fore, confirmed this conclusion making life more than somewhat difficult for any cosmologist who wished to maintain a strict Aristotelian party line. To make matters worse the stellar novae of 1572 and 1604 observed once again by Europe’s finest watchers of the heavens and determined by them to be unquestionably superlunar really put the kibosh on Aristotle’s wonderful division of the cosmos. All in all by 1610 Aristotle’s cosmology was already looking distinctly unhealthy and Galileo’s discovery of the lunar landscape far from being an unexpected deadly bolt out of the blue was just another blow helping it on its way to its grave.

Hanson might be forgiven for his over emphasis of the impact of Galileo’s lunar watercolours based obviously on his ignorance of Renaissance astronomical and cosmological history but the content of his closing paragraph displays an ignorance that I, for one, find hard to forgive. Our intrepid non-historian writes:

Galileo’s Sidereus Nuncius [emphasis in original] also included newly detailed maps of the constellations and the mention of four moons of Jupiter (although detailed observations of those were still centuries away), [my emphasis] but it was his drawings of our moon that bore the most impact on future astronomical science, realigning the heavens with a single stroke of the brush.

Having over emphasised the significance of the impact of Galileo’s lunar watercolours Hanson dismisses his discovery of the moons of Jupiter in a throwaway comment. He couldn’t demonstrate his ignorance of the material more spectacularly.

It was of course Galileo’s discovery of the four largest moons of Jupiter that caused the sensation and also did the most damage to Aristotelian cosmology, when he published the Sidereus Nuncius in 1610. Central to Aristotelian cosmology was the principle of homo-centricity, i.e. the concept that all celestial bodies, the sphere of the fixed stars and the seven planets, revolve around a common centre, the earth. The discovery of the Galilean moons, as they came to be known, was a direct empirical proof that the principle of homo-centricity was wrong. It lent indirect support to heliocentricity, which required two centres of revolution the sun for the fixed stars and the six planets and the earth for the moon. It was Galileo’s discovery of the Medician Stars, as he called them, which led to his much desired appointment as court philosophicus and mathematicus in Florence and professor of mathematics at the University of Pisa without teaching duties. Catapulting him almost overnight from being an obscure, ageing professor of mathematics to being Europe’s most notorious astronomer. The four moons of Jupiter are not “mentioned” in Sidereus Nuncius they are the reason for its hurried and secretive, to prevent anybody else beating him to the punch, composition and publication.

The illustrations of the moon in the Sidereus Nuncius are the eye candy, which the reader can admire but the far less visually spectacular diagrams of the positions of the four moons relative to Jupiter are the explosive content that make this slim pamphlet one of the most important scientific publications of all time and elevated Galileo into the pantheon of scientific heroes.

Page from Galileo's observation log displaying position of the moons relative to Jupiter

Page from Galileo’s observation log displaying position of the moons relative to Jupiter


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