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Galileo's Battle for the Heavens

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The NOVA documentary, Galileo's Battle for the Heavens, presents the struggle between Galileo and the church for his vision of the cosmos. This drama, the Galileo Affair, has been told and retold. It is the story of a man whose guide was fact and not inherited wisdom; a hero in the battle between faith and reason. In Against Method, Paul Feyerabend also presents Galileo as a heroic figure. For Feyerabend, Galileo's guide was often intuition not fact. Feyerabend believed that great science does not work the way it is painted in textbooks. And Galileo was his prime example. He showed that Galileo's commitment to Copernicism did not agree with facts known at the time. Yet it didn't stop him. In other words, Galileo himself was going more on faith than reason.

...while the pre-Copernican astronomy was in trouble (was confronted by a series of refuting instances and implausibilities), the Copernican theory was in even greater trouble (was confronted by even more drastic refuting instances and implausibilities).
Paul Fyerabend, Against Method

Galileo's Straw Man

Much has been written about Galileo's problems with the church over his Dialogue Concerning the Two Chief World Systems. In the Dialogue, Galileo's argued for the Copernican Model against the Ptolemaic Model. This was Galileo's straw man argument. In a straw man argument, you create or choose an opposing argument that is easy to defeat, then proceed to destroy it. Your own argument wins by default. The problem with Galileo's argument was that there were at least 5 "world systems"! When Galileo wrote his Dialogue, the Ptolemaic model had been already supplanted by other models [_1_] .

The 5 major planetary models that were in play when Galileo published the Dialogue were the Tychonic, Ursine, Capellan, Copernican and Keplerian. Three were geo-heliocentric (Tychonic, Capellan, Ursine) where some bodies circled the sun and some the earth. Two were heliocentric (Copernican and Keplerian). Early on, Galileo's Battle for the Heavens describes Galileo's discovery that Venus went through phases. This could only be explained if Venus was orbiting the Sun and not earth. If the choice was between a Copernican model (sun-centred) and Galileo's straw man (the earth-centred Ptolemaic) it was clear proof for the Copernican Model. But it wasn't a two-way choice. All five models mentioned were compatible with the Galileo's discovery. Galileo's Battle for the Heavens, like most discussions of the Galileo Affair, has fallen prey to Galileo's Straw Man. The program never mentions any models except for the Copernican and the Ptolemaic.

The Galileo Affair-The Elephants in the Room

Modern portrayals of the Galileo Affair are very selective with historical and scientific facts. They have to be. They often position the Galileo Affair as a clash between church and science. If that is a goal there are many scientific and historical facts that are best left untouched. They are the elephants in the room. One glaring example in Galileo's Battle for the Heavens is the fact that Galileo's contemporary, Johannes Kepler, was never mentioned once through the entire course of the program. With the Galileo Affair there are usually four elephants in the room:

  • Johannes Kepler
  • Copernicus
  • Stellar Parallax
  • Ephemerides

Kepler seems to get special treatment in Galileo's Battle for the Heavens; he is not mentioned at all. Kepler is awkward for Galileo narratives for several reasons. If Kepler's planetary model was largely correct, why did Galileo ignore him? Galileo had decided to ignore everything that Kepler did or wrote because he did not want to seek out "the nuggets of real gold in Kepler's heap of dross" [_2_] . This means that he ignored his 3 laws of planetary motion, his belief that the tides were caused by the moon, and his suggested design for refracting telescopes. Kepler's design of telescope, which used convex lenses for both the eyepiece and objective, would replace Galileo's design within a decade of Galileo's death.

Kepler's relation with the church is also awkward for Galileo narratives. The Galileo Affair is used to argue a clash between church and science. But why should it be more important than the fact that Kepler's most loyal supporters through the last decades of his life were Jesuit priests from Austria. And Kepler wasn't even Catholic, he was an excommunicate Lutheran. Kepler used the network of Jesuit institutions as his private postal service. It was the Jesuits who were the first champions of Kepler's refracting telescope design (see Jesuits and the Early Telescope). The Jesuits chased down and returned a manuscript that had been stolen from Kepler. They even had their master telescope maker, Niccolo Zucchi, build him a telescope. Kepler used the preface of his last book, the Somnium, to thank them for their loyalty. Outside of the Jesuits, it was a French Catholic priest who arranged an international experiment that became the first important support for Kepler's planetary model (see Gassendi's Transit).

Copernicus usually fares better than Kepler in Galileo narratives; at least he gets a mention. Curiously, Copernicus's own encounters with the church are rarely mentioned. He had many (see Copernicus Timeline). Copernicus was orphaned at about the age of 10. From that time until his death he was either in the employ or care of the church. The church paid for his education at some of the best universities in Europe, and gave him the position of canon at a Polish diocese after graduation. The church had a deep respect for his competence, and depended on his advice in diplomacy, economics, medicine, military defence and astronomy. It is not commonly known, but Copernicus derived two important laws of economics that are commonly attributed to others; Gresham's Law and the Quantity Theory of Money. When the Vatican found out about his new model of planetary motion, it sent him a letter asking him to share his work with others, and offered to pay for its publication (see Schonberg's Letter). Copernicus ignored the request. At the urging of a German professor (Rheticus) and a Polish bishop (Tiedeman Geise) he finally agreed to publish his work, but only as a series of tables, not an explanation of his theory. It was Bishop Geise that convinced him to publish the explanation as well [_3_] . Copernicus fell ill before the publication of his work and was cared for by a canon of the church at the urging of another Catholic bishop (Danticus). After Copernicus' death he was honoured by being buried inside a cathedral, near the altar he had tended during his life [_4_] .

The Copernican model featured a moving earth with the sun being stationary. There are necessary consequences of a moving earth. One is stellar parallax (see Copernicus and Stellar Parallax). If the earth was moving relative to the sun it demands that viewers on earth be able to see some change in the relative positions of nearer and distant stars over the course of a year. No-one in Galileo's time was able to detect any change in the positions of the different stars. Stellar parallax was eventually detected, but not until 1838.

A measure for any scientific model is how well it fits the data. This applies to planetary models too. Man has been observing and recording the position of planets and stars for thousands of years. A collection of these records is known as an ephemeris (pl. ephemerides). Since planetary models can be used to predict the positions of planets through the year, deciding on a model should have been as easy as comparing predicted positions with an ephemeris for each of the different models. But it seemed that all the models (excepting the Keplerian) were observationally equivalent. This has been confirmed by modern computer-aided analyses [_5_] . The Copernican Model used perfect circles when an accurate model required the use of Kepler's ellipses. Galileo, his contemporaries and even Copernicus knew that the Copernican Model did not seem to fit the data any better than its competing models.

The Galileo Myths

Narratives such as Galileo's Battle for the Heavens unnecessarily embellish his record with myth and hyperbole. Galileo doesn't need their help. His works, especially in classical mechanics, stand on their own. Unfortunately, because of this hyperbole, it is difficult to know where the real Galileo ends and where the mythical Galileo begins .

Galileo's Battle for the Heavens and its associated website repeats several of the most common Galileo myths (see The Galileo Myths). This from an award-winning documentary that is used widely in science education. Modern astronomical telescopes do not derive from Galileo's design but from Kepler's design (see Myth 5,The Galileo Myths). Galileo was not the first to apply mathematics to nature. This tradition had been established centuries before by the The Oxford Calculators and the Parisian Doctors (see Myth 6,The Galileo Myths). Several of the proofs and laws credited to Galileo had been published centuries before by Nicole Oresme, a Roman Catholic Bishop (see Myth 10,The Galileo Myths). Galileo was not a lone voice for experimentation or a lone voice against Aristotle (see Myth 9,The Galileo Myths). Galileo's Tower of Pisa experiment is not a good example of Galileo's belief in experimentation because it never happened (see Myth 1,The Galileo Myths) . Neither was Galileo able to determine the rate of acceleration due to gravity unless you consider a 50% error close enough [_6_] . It was the Jesuit scientists from Galileo's time that were the first to derive an accurate estimate of the acceleration due to gravity (see Galileo's Contemporaries). And Galileo was not "remanded to a small room in the Palace of the Inquisition". It was a massive 5-room suite that came with a personal valet and room service that included the finest of Tuscan food (see Myth 3,The Galileo Myths). A floor plan of the suite is shown below.

Galileo's Vatican Suite

Galileo and the Church

Galileo's own problems with the church over the Copernican Model are well-known. He was eventually placed under house arrest in a large summer villa, Il Gioello, that Galileo had been renting from one of the richest banking families in Florence (the Martellinis). "House arrest" didn't mean quite the same thing to the Roman Inquisition as it does today. It was most often a restriction of movement. If the sentence really involved a house arrest, there would have been no need to specify that he shouldn't cross the Arno, which was about 2 kilometers from his villa. At the time Galileo was 69. Until that time, Galileo had enjoyed the favour of the church. This included monetary support for his research. When Pope Urban VIII was elected pope, he arranged for two prebends for Galileo. Prebends are similar to sinecures, a recurring grant with little associated responsibilities [_7_] . Galileo did have disputes with several Jesuits but for the most part these were scientific disputes, as happen even today. Throughout his life he remained close to many Roman Catholic clergy. Two priests, Pierre Gassendi and Marin Mersenne, could be considered Galileo's ambassadors outside of Italy. One of his 'prisons' during his trial was the palace of one of his best friends, Archbishop Piccolomini of Siena. Although the Inquisition considered his stay there as a "formal prison", few others would. Throughout his stay, he was wined and dined by his friend. In fact Galileo's daughter was very concerned that her father may overindulge in 'prison' and thereby endanger his health [_8_] .

A Hollow Victory

By the end of Galileo's Battle for the Heavens, the program had successfully built and destroyed a straw man and had successfully navigated around all the elephants in the room in the Galileo Affair. It is a hollow victory. In the process it missed the most important scientific issues. That is because the program, like many discussions of the Galileo Affair, was not about science. This is signalled by the program's own byline: "Witness Galileo's famous struggle to persuade church authorities of the truth behind his discoveries about the cosmos". Persuading people of the truth is the stuff of debating clubs not scientists. Being right is not good enough in science. 'How' you are right matters. Your proofs must be valid. This is as true today as it was 400 years ago (see Wegener and Galileo).


Copyright Joseph Sant (2016).
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1. Michael Hoskin, Cambridge University Press 1999, Cambridge Concise History of Astronomy, , 117
By the time the Dialogue had been published most of those believing in an earth-centered system had adopted one of the geo-heliocentric systems.
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2. Max Caspar, Courier Dover Publications 1993, Kepler, , 137
Caspar refers to this quote from an article by Rosen in the footnotes of his discussion as to why Galileo may have chosen to ignore Kepler through the last three decades of his life.
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3. Repcheck, Jack, Simon and Schuster,, Copernicus' Secret: How the Scientific Revolution Began, , p.147-148
Repcheck quotes Rheticus's own words in crediting Giese in convincing Copernicus to publish. The book also discusses Copernicus's own argument for NOT publishing his theory.
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4. Goddu, Andre, Brill Academic Publishers, Copernicus and the Aristotelian Tradition, , p. 436
Based on custom, Copernicus should have been buried near the altar he was responsible for, the altar of Saint Vaclav. On exhuming bodies near the altar, a corpse matching the age of Copernicus was found, and the DNA of this corpse matched that of a hair found in one of Copernicus's books.
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5. Babb, Stanley E.,, Isis, Sept. 1977, Accuracy of Planetary Theories, Particularly for Mars,, , pp. 426-34
In this article Stanley Babb compares the predictions of the Copernican and Ptolemaic models against the actual planetary positions using computer-based statistical analysis. The results did not show a dramatic difference between the two systems, but the earth-centred system (the Ptolemaic) did perform better for planets such as Mars.
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6. I. Bernard Cohen, W. W. Norton and Company, 1985, The birth of a new physics, , 97
Cohen mentions that Galileo's estimate of the acceleration due to gravity has been calculated to be 467 cm/sec/sec versus the actual value of 980 cm/sec/sec. The estimate produced by the Jesuit experiment from the Torre Asinelli was 914 cm/sec/sec.
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7. Rowland,Wade, Arcade Publishing, Galileo's Mistake, , 57
Galileo was the beneficiary of two prebends from the diocese of Pisa and the diocese of Brescia. Typically prebends provide a right to a share of the revenue of a diocese or parish in return for some associated responsibilities. But there were no responsibilities. Not even to ever show up in either Pisa or Brescia. It is reasonable to interpret the prebends as ongoing (research) grants which Galileo could spend as he pleased. There is no indication that these prebends were ever revoked even after his trial.
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8. Sobel, Dava., Bloomsbury Publishing USA, 1999., Galileo's daughter: A historical memoir of science, faith and love., , pp. 279
This is a collection of letters from one of Galileo's daughters to him while he was in Rome and Siena. She expressed her concern about his habit of overindulging.
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