Galileo Galilei (564 - 1642)

Galileo Galilei (February 15, 1564 - January 8, 1642), was a Tuscan astronomer, philosopher, and physicist who is closely associated with the Scientific Revolution. Galileo was born in Pisa and his career coincided with that of Kepler. The work of Galileo is considered to be a significant break from that of Aristotle; in particular, Galileo placed emphasis on quantity, rather than quality.

Experimental science
In the pantheon of the scientific revolution Galileo occupies a high position because of his pioneering use of quantitative experiments with results analyzed mathematically. There was no tradition of such methods in European thought at that time; the great experimentalist who immediately preceded Galileo, William Gilbert, did not use a quantitative approach. In the 20th century the reality of Galileo's experiments was challenged by some authorities, in particular the distinguished French historian of science Alexandre Koyré. The experiments on falling bodies (actually rolling balls) were replicated using the methods described by Galileo (Settle, 1961), and the precision of the results was consistent with Galileo's report. Later research into Galileo's unpublished working papers from as early as 1604 clearly showed the reality of the experiments and even indicated the particular results that led to the time-squared law (Drake, 1973).

Galileo was one of the first people to use the telescope to observe the sky. Galileo Galilei's discovery of the moons of Jupiter. For a translation from Sidereus Nuncius click on the picture.On January 7th 1610 Galileo discovered Jupiter's four largest satellites (moons): Io, Europa, Ganymede, and Callisto. (Later astronomers overruled Galileo's naming of these objects, changing his Medicean stars to Galilean satellites.) Galileo noted that Venus exhibited a full set of phases like the Moon. Because the apparent brightness of Venus is nearly constant, Galileo reasoned that Venus could not be circling the Earth at a constant distance. Galileo was one of the first Europeans to observe sunspots, although there is evidence that Chinese astronomers had done so before. Physics

Galileo's theoretical and experimental work on the motions of bodies, along with the largely independent work of Kepler and Descartes, was a precursor of the Classical mechanics developed by Sir Isaac Newton. Galileo also noted that a pendulum's swings always take the same amount of time, independently of the amplitude. While Galileo believed this equality of period to be exact, it is only approximate, applying to small swings. In the early 1600s, Galileo and an assistant tried to measure the speed of light. At a distance of less than a mile, Galileo could detect no delay in the round-trip time greater than when he and the assistant were only a few yards apart. While Galileo's application of mathematics to experimental physics was innovative, his mathematical methods were the standard ones of the day. Galileo produced one piece of original and even prophetic work in mathematics: Galileo's paradox, which shows that there are as many perfect squares as there are whole numbers, even though most numbers are not perfect squares. 

Galileo made a few contributions to what we now call technology as distinct from pure physics, and suggested others. In 1595 - 1598 Galileo devised and improved a "Geometric and Military Compass" suitable for use by gunners and surveyors. Church controversy

Galileo was a devout Catholic, yet his writings on Copernican heliocentrism disturbed some in the Catholic Church, who believed in a geocentric model of the solar system. For his insights, Galileo was threatened with death at the stake and would eventually face lifelong house arrest after recanting his claims.

The geocentric model was generally accepted at the time for several reasons. By the time of the controversy, the Catholic Church had largely abandoned the Ptolemaic model for the Tychonian model in which the Earth was at the centre of the Universe, the Sun revolved around the Earth and the other planets revolved around the Sun. The first to defend Galileo was a Benedictine abbot, Benedetto Castelli, who was also a professor of mathematics and a former student of Galileo's. It was this exchange that led Galileo to write the Letter to Grand Duchess Christina. (Castelli remained Galileo's friend, visiting him at Arcetri near the end of Galileo's life, after months of effort to get permission from the Inquisition to do so.)

However, real power lay with the Church, and Galileo's arguments were most fiercely fought on the religious level. The Church authorities gave Caccini promotion. Father Lorini proved that Galileo's doctrine was not only heretical but "atheistic," and besought the Inquisition to intervene. The Bishop of Fiesole screamed in rage against the Copernican system, publicly insulted Galileo, and denounced him to the Grand-Duke. The Archbishop of Pisa secretly sought to entrap Galileo and deliver him to the Inquisition at Rome. (White, 1898; online text (http://www.santafe.edu/~shalizi/White/astronomy/war.html))

When Galileo was tried in 1633, the Inquisition was proceeding on the premise that he had been ordered not to teach it at all, based on a paper in the records from 1616; but Galileo produced a letter from Cardinal Bellarmine that showed only the "hold or defend" order. The Roman Inquisition had rejected earlier pleas by Galileo to postpone or relocate the trial because of his ill health. Galileo arrived in Rome for his trial before the Inquisition on February 13, 1633. On April 12, 1633, Galileo was brought to trial, and the formal interrogation by the Inquisition began. During this interrogation Galileo stated that he did not defend the Copernican theory, and cited a letter of Cardinal Bellarmine from 1615 to support this contention. In a second hearing on April 30, Galileo confessed to having erred in the writing of the book, through vain ambition, ignorance, and inadvertence. He was then allowed to return to the home of the Tuscan ambassador. On June 22, 1633, the Inquisition held the final hearing on Galileo, who was then 69 years old and pleaded for mercy, pointing to his "regrettable state of physical unwellness". The tale that Galileo, rising from his knees after recanting, said "Eppur si muove!" A Spanish painting, dated 1643 or possibly 1645, shows Galileo writing the phrase on the wall of a dungeon cell. Here we have a second version of the story, which also cannot be true, because Galileo was never imprisoned in a dungeon; but the painting shows that some story of "Eppur si muove" was circulating in Galileo's time. Galileo was sentenced to prison, but because of his advanced age (and/or Church politics) the sentence was commuted to house arrest at his villas in Arcetri and Florence[1] (http://www.lucidcafe.com/library/96feb/galileo.html). Though the sentence announced against Galileo mentioned no other works, Galileo found out two years later that publication of anything he might ever write had been quietly banned. Moreover, deeper examination of the primary sources for Galileo and his trial shows that claims of torture and deprivation were likely exaggerated. Dava Sobel's Galileo's Daughter offers a different set of insights into Galileo and his world, in large part through the private correspondence of Maria Celeste, the daughter of the title, and her father.

In 1992, 359 years after the Galileo trial, Pope John Paul II issued an apology, lifting the edict of Inquisition against Galileo: "Galileo sensed in his scientific research the presence of the Creator who, stirring in the depths of his spirit, stimulated him, anticipating and assisting his intuitions."


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