page_title: Galileo affair
section_title: Initial controversies
hierarchical_section_title: Galileo affair / Initial controversies
caption_attribution_description: English: Representation of Ptolemy. Previously published in Les vrais pourtraits et vies des hommes illustres grecz, latins, et payens recueilliz de leurs tableaux livres et medalles antiques, et modernes. Par Andre Thevet angoumoysin, premier cosmographe du roy., premier tome, livre II, chap. 41, "Claude Ptolemee Pelusien", p. 87. Published by Blanche Marantin and Guillaume Chaudiere, Paris, 1584.
context_page_description: The Galileo affair began around 1610 and culminated with the trial and condemnation of Galileo Galilei by the Roman Catholic Inquisition in 1633. Galileo was prosecuted for his support of heliocentrism, the astronomical model in which the Earth and planets revolve around the Sun at the centre of the Solar System.
  In 1610, Galileo published his Sidereus Nuncius, describing the surprising observations that he had made with the new telescope, among them, the Galilean moons of Jupiter. With these observations and additional observations that followed, such as the phases of Venus, he promoted the heliocentric theory of Nicolaus Copernicus published in De revolutionibus orbium coelestium in 1543. Galileo's discoveries were met with opposition within the Catholic Church, and in 1616 the Inquisition declared heliocentrism to be "formally heretical." Heliocentric books were banned and Galileo was ordered to abstain from holding, teaching or defending heliocentric ideas.
  Galileo went on to propose a theory of tides in 1616, and of comets in 1619; he argued that the tides were evidence for the motion of the Earth.
context_section_description: Galileo began his telescopic observations in the later part of 1609, and by March 1610 was able to publish a small book, The Starry Messenger (Sidereus Nuncius), describing some of his discoveries: mountains on the Moon, lesser moons in orbit around Jupiter, and the resolution of what had been thought to be very cloudy masses in the sky (nebulae) into collections of stars too faint to see individually without a telescope. Other observations followed, including the phases of Venus and the existence of sunspots.
  Galileo's contributions caused difficulties for theologians and natural philosophers of the time, as they contradicted scientific and philosophical ideas based on those of Aristotle and Ptolemy and closely associated with the Catholic Church. In particular, Galileo's observations of the phases of Venus, which showed it to circle the Sun, and the observation of moons orbiting Jupiter, contradicted the geocentric model of Ptolemy, which was backed and accepted by the Roman Catholic Church, and supported the Copernican model advanced by Galileo.
  Jesuit astronomers, experts both in Church teachings, science, and in natural philosophy, were at first skeptical and hostile to the new ideas; however, within a year or two the availability of good telescopes enabled them to repeat the observations. In 1611, Galileo visited the Collegium Romanum in Rome, where the Jesuit astronomers by that time had repeated his observations. Christoph Grienberger, one of the Jesuit scholars on the faculty, sympathized with Galileo's theories, but was asked to defend the Aristotelian viewpoint by Claudio Acquaviva, the Father General of the Jesuits. Not all of Galileo's claims were completely accepted: Christopher Clavius, the most distinguished astronomer of his age, never was reconciled to the idea of mountains on the Moon, and outside the collegium many still disputed the reality of the observations. In a letter to Kepler of August 1610, Galileo complained that some of the philosophers who opposed his discoveries had refused even to look through a telescope:
  My dear Kepler, I wish that we might laugh at the remarkable stupidity of the common herd. What do you have to say about the principal philosophers of this academy who are filled with the stubbornness of an asp and do not want to look at either the planets, the moon or the telescope, even though I have freely and deliberately offered them the opportunity a thousand times? Truly, just as the asp stops its ears, so do these philosophers shut their eyes to the light of truth.
  Geocentrists who did verify and accept Galileo's findings had an alternative to Ptolemy's model in an alternative geocentric (or "geo-heliocentric") model proposed some decades earlier by Tycho Brahe – a model, in which, for example, Venus circled the Sun. Brahe argued that the distance to the stars in the Copernican system would have to be 700 times greater than the distance from the Sun to Saturn. Moreover, the only way the stars could be so distant and still appear the sizes they do in the sky would be if even average stars were gigantic – at least as big as the orbit of the Earth, and of course vastly larger than the sun (refer to article on Tychonic System and Stellar parallax).
  Galileo became involved in a dispute over priority in the discovery of sunspots with Christoph Scheiner, a Jesuit. This became a bitter lifelong feud. Neither of them, however, was the first to recognise sunspots – the Chinese had already been familiar with them for centuries.
  At this time, Galileo also engaged in a dispute over the reasons that objects float or sink in water, siding with Archimedes against Aristotle. The debate was unfriendly, and Galileo's blunt and sometimes sarcastic style, though not extraordinary in academic debates of the time, made him enemies. During this controversy one of Galileo's friends, the painter Lodovico Cardi da Cigoli, informed him that a group of malicious opponents, which Cigoli subsequently referred to derisively as "the Pigeon league", was plotting to cause him trouble over the motion of the Earth
caption: Claudius Ptolemy (A.D. 90–168), whose geocentric system was adopted by the Catholic Church,[3][4] and supplanted by the work of Copernicus and Galileo in the 16th and 17th centuries.
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