Galileo Galilei

Galileo Galilei (Pisa, February 15, 1564 – Arcetri, January 8, 1642), was a Tuscan astronomer, philosopher, and physicist who is closely associated with the scientific revolution. His achievements include improvements to the telescope, a variety of astronomical observations, the first law of motion, and effective support for Copernicanism. He has been referred to as the "father of modern astronomy," as the "father of modern physics," and as "father of science." His experimental work is widely considered complementary to the writings of Francis Bacon in establishing the modern scientific method. Galileo's career coincided with that of Johannes Kepler. The work of Galileo is considered to be a significant break from that of Aristotle. In addition, his conflict with the Catholic Church is taken as a major early example of the conflict of authority and freedom of thought, particularly with science, in Western society.

Early career

Galileo was born in Pisa, Italy, the son of Vincenzo Galilei, a mathematician and musician.

Galileo as a teacher in Padua, Galileo Stamps

He attended the University of Pisa, but was forced to cease his study there for financial reasons. However, he was offered a position on its faculty in 1589 and taught mathematics. Soon after, he moved to the University of Padua, and served on its faculty teaching geometry, mechanics, and astronomy until 1610. During this time he explored science and made many landmark discoveries.

Experimental science

In the pantheon of the scientific revolution, Galileo takes 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. However, Galileo's father, Vincenzo Galilei, had performed experiments in which he discovered what may be the oldest known non-linear relation in physics, between the tension and the pitch of a stretched string. Galileo also contributed to the rejection of blind allegiance to authority (like the Church) or other thinkers (such as Aristotle) in matters of science and to the separation of science from philosophy or religion. These are the primary justifications for his description as the "father of science."

In the 20th century some authorities challenged the reality of Galileo's experiments, in particular the distinguished French historian of science Alexandre Koyré. The experiments reported in Two New Sciences to determine the law of acceleration of falling bodies, for instance, required accurate measurements of time, which appeared to be impossible with the technology of the 1600s. According to Koyré, the law was arrived at deductively, and the experiments were merely illustrative thought experiments.

Later research, however, has validated the experiments. 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).


Although the popular idea of Galileo inventing the telescope is inaccurate, he was one of the first people to use the telescope to observe the sky. Based on sketchy descriptions of telescopes invented in the Netherlands in 1608, Galileo made one with about 8x magnification, and then made improved models up to about 20x. On August 25, 1609, he demonstrated his first telescope to Venetian lawmakers. His work on the device also made for a profitable sideline with merchants who found it useful for their shipping businesses. He published his initial telescopic astronomical observations in March 1610 in a short treatise entitled Sidereus Nuncius (Sidereal Messenger).

It was on this page that Galileo first noted an observation of the moons of Jupiter. This observation upset the notion that all celestial bodies must revolve around the Earth. Galileo published a full description in Sidereus Nuncius in March 1610.

On January 7, 1610 Galileo discovered three of Jupiter's four largest satellites (moons): Io, Europa, and Callisto. Ganymede he discovered four nights later. He determined that these moons were orbiting the planet since they would appear and disappear; something he attributed to their movement behind Jupiter. He made additional observations of them in 1620. Later astronomers overruled Galileo's naming of these objects, changing his Medicean stars to Galilean satellites. The demonstration that a planet had smaller planets orbiting it was problematic for the orderly, comprehensive picture of the geocentric model of the universe, in which everything circled around the Earth.

Galileo noted that Venus exhibited a full set of phases like the Moon. The heliocentric model of the solar system developed by Copernicus predicted that all phases would be visible since the orbit of Venus around the Sun would cause its illuminated hemisphere to face the Earth when it was on the opposite side of the Sun and to face away from the Earth when it was on the Earth-side of the Sun. By contrast, the geocentric model of Ptolemy predicted that only crescent and new phases would be seen, since Venus was thought to remain between the Sun and Earth during its orbit around the Earth. Galileo's observation of the phases of Venus proved that Venus orbited the Sun and lent support to (but did not prove) the heliocentric model.

Galileo was one of the first Europeans to observe sunspots, although there is evidence that Chinese astronomers had done so before. The very existence of sunspots showed another difficulty with the perfection of the heavens as assumed in the older philosophy. And the annual variations in their motions, first noticed by Francesco Sizzi, presented great difficulties for either the geocentric system or that of Tycho Brahe. A dispute over priority in the discovery of sunspots led to a long and bitter feud with Christoph Scheiner; in fact, there can be little doubt that both of them were beaten by David Fabricius and his son Johannes.

He was the first to report lunar mountains and craters, whose existence he deduced from the patterns of light and shadow on the Moon's surface. He even estimated the mountains' heights from these observations. This led him to the conclusion that the Moon was "rough and uneven, and just like the surface of the Earth itself", and not a perfect sphere as Aristotle had claimed.

Galileo observed the Milky Way, previously believed to be nebulous, and found it to be a multitude of stars, packed so densely that they appeared to be clouds from Earth. He also located many other stars too distant to be visible with the naked eye.

Galileo observed the planet Neptune in 1612, but did not realize that it was a planet and took no particular notice of it. It appears in his notebooks as one of many unremarkable dim stars.


Galileo's theoretical and experimental work on the motions of bodies, along with the largely independent work of Kepler and René Descartes, was a precursor of the Classical mechanics developed by Sir Isaac Newton. He was a pioneer, at least in the European tradition, in performing rigorous experiments and insisting on a mathematical description of the laws of nature.

One of the most famous stories about Galileo is that he dropped balls of different masses from the Leaning Tower of Pisa to demonstrate that their velocity of descent was independent of their mass (excluding the limited effect of air resistance). This was contrary to what Aristotle had taught: that heavy objects fall faster than lighter ones, in direct proportion to weight. Though the story of the tower first appeared in a biography by Galileo's pupil Vincenzo Viviani, it is not now generally accepted as true. However, Galileo did perform experiments involving rolling balls down inclined planes, which proved the same thing: falling or rolling objects (rolling is a slower version of falling) are accelerated independently of their mass.

He determined the correct mathematical law for acceleration: the total distance covered, starting from rest, is proportional to the square of the time (This law is regarded as a predecessor to the many later scientific laws expressed in mathematical form.). He also concluded that objects retain their velocity unless a force —often friction— acts upon them, refuting the accepted Aristotelian hypothesis that objects "naturally" slow down and stop unless a force acts upon them. This principle was incorporated into Newton's laws of motion (1st law).

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 an approximation appropriate to small amplitudes. It is good enough to regulate a clock, however, as Galileo may have been the first to realize. (See Technology below)

In the early 1600s, Galileo and an assistant tried to measure the speed of light. They stood on different hilltops, each holding a shuttered lantern. Galileo would open his shutter, and, as soon as his assistant saw the flash, he would open his shutter. 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 he could reach no conclusion on whether light propagated instantaneously, he recognized that the distance between the hilltops was perhaps too small for a good measurement.

Galileo is lesser known for, yet still credited with being one of the first to understand sound frequency. After scraping a chisel at different speeds, he linked the pitch of sound to the spacing of the chisel's skips (frequency).

In his 1632 Dialogue Galileo presented a physical theory to account for tides, based on the motion of the Earth. If correct, this would have been a strong argument for the reality of the Earth's motion. (The original title for the book, in fact, described it as a dialogue on the tides; the reference to tides was removed by order of the Inquisition.) His theory gave the first insight into the importance of the shapes of ocean basins in the size and timing of tides; he correctly accounted, for instance, for the negligible tides halfway along the Adriatic Sea compared to those at the ends. As a general account of the cause of tides, however, his theory was a failure.

Galileo also put forward the basic principle of relativity, that the laws of phsyics are the same in any system that is moving at a steady speed in a straight line, regardless of its particular speed or direction. Hence, there is no absolute motion or absolute rest. This principle provided the basic framework for Newton's laws of motion and Einstein's theory of relativity.


While Galileo's application of mathematics to experimental physics was innovative, his mathematical methods were the standard ones of the day. The analyses and proofs relied heavily on the Eudoxian theory of proportion, as set forth in the fifth book of Euclid's Elements. This theory had become available only a century before, thanks to accurate translations by Tartaglia and others; but by the end of Galileo's life it was being superseded by the algebraic methods of Descartes, which a modern finds incomparably easier to follow.

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. Such seeming contradictions were brought under control 250 years later in the work of Georg Cantor.


Galileo made a few contributions to what we now call technology as distinct from pure physics, and suggested others. This is not the same distinction as made by Aristotle, who would have considered all Galileo's physics as techne or useful knowledge, as opposed to episteme, or philosophical investigation into the causes of things.

In 1595–1598, Galileo devised and improved a "Geometric and Military Compass" suitable for use by gunners and surveyors. This expanded on earlier instruments designed by Niccolo Tartaglia and Guidobaldo del Monte. For gunners, it offered, in addition to a new and safer way of elevating cannons accurately, a way of quickly computing the charge of gunpowder for cannonballs of different sizes and materials. As a geometric instrument, it enabled the construction of any regular polygon, computation of the area of any polygon or circular sector, and a variety of other calculations.

About 1606–1607 (or possibly earlier), Galileo made a thermometer, using the expansion and contraction of air in a bulb to move water in an attached tube.

Galileo explains the use of a telescope

In 1609, Galileo was among the first to use a refracting telescope as an instrument to observe stars, planets or moons.

In 1610, he used a telescope as a compound microscope, and he made improved microscopes in 1623 and after. This appears to be the first clearly documented use of the compound microscope.

In 1612, having determined the orbital periods of Jupiter's satellites, Galileo proposed that with sufficiently accurate knowledge of their orbits one could use their positions as a universal clock, and this would make possible the determination of longitude. He worked on this problem from time to time during the remainder of his life; but the practical problems were severe. The method was first successfully applied by Giovanni Domenico Cassini in 1681 and was later used extensively for land surveys; for navigation, the first practical method was the chronometer of John Harrison.

In his last year, when totally blind, he designed an escapement mechanism for a pendulum clock. The first fully operational pendulum clock was made by Christiaan Huygens in the 1650s.

He created sketches of various inventions, such as a candle and mirror combination to reflect light throughout a building, an automatic tomato picker, a pocket comb that doubled as an eating utensil, and what appears to be a ballpoint pen.

Church controversy

Galileo was a practicing Catholic, yet his writings on Copernican heliocentrism disturbed some in the Catholic Church who believed in a geocentric model of the solar system. They argued that heliocentrism was in direct contradiction of the Bible (Joshua 10:12): "Then spake Joshua to the Lord in the day when the Lord delivered up the Amorites before the children of Israel, and he said in the sight of Israel, 'Sun, stand thou still upon Gibeon; and thou, Moon, in the valley of Ajalon'." Such Bible passages could be literally interpreted as asserting that the Sun and the Moon were both objects peripheral to the Earth; they could be given a more symbolic, metaphysical interpretation (e.g., their representing a highly illuminated state of consciousness (the Sun founded upon Gibeon) and a phase of lower reflected intellect (the Moon in the valley of Ajalon) or thought); or they could be taken as simply a description of the appearance of the heavens as seen from Earth. At that time the most literal Biblical interpretation was prevalent with the church hierarchy, especially among the Dominican Order, facilitators of the Inquisition; it was also in line with the highly revered ancient writings of Aristotle and Plato.

The geocentric model was generally accepted at the time, as it had been since philosophers first considered the heavens. By the time of the controversy, the Ptolemaic model had a serious rival in the Tychonian model in which the Earth was at the center of the Universe, the Sun revolved around the Earth and the other planets revolved around the Sun. This model is geometrically equivalent to the Copernican model and agreed with observations in that it predicted no parallax of the stars, an effect that was impossible to detect with the instruments of the time. In the view of Tycho and many others, this model explained the observable data of the time better than the geocentric model did. (That inference is valid, however, only on the assumption that no very small effect had been missed: that the instruments of the time were absolutely perfect, or that the Universe could not be much larger than was generally believed at the time. As to the latter, belief in the large, possibly infinite, size of the Universe was part of the heretical beliefs for which Giordano Bruno had been burned at the stake in 1600.)

An understanding of the controversies, if it is even possible, requires attention not only to the politics of religious organizations but to those of academic philosophy. Before Galileo had trouble with the Jesuits and before the Dominican friar Caccini denounced him from the pulpit, his employer heard him accused of contradicting Scripture by a professor of philosophy, Cosimo Boscaglia, who was neither a theologian nor a priest. Galileo was defended on the spot by a Benedictine abbot, Benedetto Castelli, who was also a professor of mathematics and a former student of Galileo's. It was this exchange, reported to Galileo by Castelli, 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.)

There is evidence of an organized and secretive opposition to Galileo among some academic philosophers. This included professors against whom Galileo, who was not officially a philosopher at all, had successfully argued for the theory of buoyancy developed by Archimedes, as against that of Aristotle, which had been taught in the academies. Moreover, the new telescopic discoveries in astronomy were, even without arguments on heliocentrism, upsetting the established comprehensive theory of the heavens, again due to Aristotle. The Jesuit astronomers, after a period of disbelief when good telescopes were almost unobtainable, had soon enough agreed on the validity of Galileo's discoveries; by contrast, some professors of the secular academic world refused for a time to look through the telescope. Caccini's attack, if not actually inspired by the philosophers, was welcomed by them and had their support.

However, real power lay with the Church, and Galileo's arguments were most fiercely fought on the religious level. The late nineteenth and early twentieth century historian Andrew Dickson White wrote from an anti-clerical perspective:

The war became more and more bitter. The Dominican Father Caccini preached a sermon from the text, "Ye men of Galilee, why stand ye gazing up into heaven?" and this wretched pun upon the great astronomer's name ushered in sharper weapons; for, before Caccini ended, he insisted that "geometry is of the devil," and that "mathematicians should be banished as the authors of all heresies." 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. The Archbishop of Florence solemnly condemned the new doctrines as unscriptural; and Paul V, while petting Galileo, and inviting him as the greatest astronomer of the world to visit Rome, was secretly moving the Archbishop of Pisa to pick up evidence against the astronomer.

Cardinal Robert Bellarmine

Cardinal Robert Bellarmine, one of the most respected Catholic theologians of the time, was called on to adjudicate the dispute between Galileo and his opponents, including both religious zealots and secular university professors. The appointment shows the world view that prevailed before the Scientific Revolution: a leading theologian was assigned to tell scholars what views they were allowed to "hold or defend" concerning the workings of the physical world.

Bellarmine insisted that Galileo furnish more adequate proof of his new theories before he would be allowed to teach them as true or even as probably true. Until such proof was forthcoming, the ideas should only be taught as hypothesis, in the old sense of the word: that is, as calculating tricks that were not to be considered as in any way real.

This put Galileo in a difficult position, as he had no conclusive proof for his position. In fact, his theories had gaps and errors, as is (we now know) the usual condition of radically new scientific work. The real meaning of the requirement for better proof became clear in the 1630s, when Galileo was condemned by the Inquisition because of his book Dialogue Concerning the Two Chief World Systems. That book contained what Galileo considered to be a physical proof of the Earth's motion, based on the tides; had it been correct (which it was not), it would have satisfied Bellarmine's requirement. In the event, the Inquisition did not even consider whether the argument was right or wrong. It condemned Galileo simply for publishing, ignoring Bellarmine's reasoning.

While many in the Church supported Galileo, the charges brought by the priests who had been goaded to act against him were serious. These men asserted that dreadful consequences must result to Christian theology were the heavenly bodies proved to revolve about the Sun and not about the Earth. Their most tremendous dogmatic engine was the statement that "his pretended discovery vitiates the whole Christian plan of salvation." Father Lecazre declared, "It casts suspicion on the doctrine of the incarnation." Others declared, "It upsets the whole basis of theology. If the Earth is a planet, and only one among several planets, it can not be that any such great things have been done specially for it as the Christian doctrine teaches. If there are other planets, since God makes nothing in vain, they must be inhabited; but how can their inhabitants be descended from Adam? How can they trace back their origin to Noah's ark? How can they have been redeemed by the Saviour?" Nor was this argument confined to the theologians of the Roman Church; Melanchthon, Protestant as he was, had already used it in his attacks on Copernicus and his school. (White, 1898; online text)

In 1616, the Inquisition warned Galileo not to hold or defend the hypothesis asserted in Copernicus's On the Revolutions, though it has been debated whether he was admonished not to "teach in any way" the heliocentric theory. Copernicus's book was not condemned, rather, it was just held pending the correction of a few sentences. 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 latter is in Bellarmine's own hand and of unquestioned authenticity; the former is an unsigned copy, violating the Inquisition's own rule that the record of such an admonition had to be signed by all parties and notarized. Leaving aside technical rules of evidence, what can one conclude as to the real events? There are two schools of thought. According to Stillman Drake, the order not to teach was delivered unofficially and improperly; Bellarmine would not allow a formal record to be made, and assured Galileo in writing that the only order in effect was not to "defend or hold". According to Giorgio di Santillana, however, the unsigned minute was simply a fabrication by the Inquisition.

In 1623 Pope Gregory XV died, and Galileo's close friend Maffeo Barberini became Pope Urban VIII. The new Pope gave Galileo vague permission to ignore the ban and write a book about his opinions, so long as he did not openly support his theory. Galileo consented, and set to work writing his masterpiece, Dialogue Concerning the Two Chief World Systems (often called simply the Dialogue). It involved an argument between two intellectuals, one geocentric, the other heliocentric, and a layman, neutral but interested. Although it presented the Church's point of view, the geocentrist was depicted foolishly, while the heliocentrist often dominated the argument and convinced the neutral member in the end.

The Dialogue was published in 1632 with the approval of Catholic censors. It was applauded by intellectuals but nevertheless aroused the Church's ire. Despite his continued insistence that his work in the area was purely theoretical, despite his strict following of the church protocol for publication of works (which required prior examination by church censors and subsequent permission), and despite his former friendship with the Pope (who presided throughout the ordeal), Galileo was summoned to trial before the Roman Inquisition in 1633.

The Inquisition had rejected earlier pleas by Galileo to postpone or relocate the trial because of his ill health. At a meeting presided by Pope Urban VIII, the Inquisition decided to notify Galileo that he either had to come to Rome or that he would be arrested and brought there in chains. Galileo arrived in Rome for his trial before the Inquisition on February 13, 1633. After two weeks in quarantine, Galileo was detained at the comfortable residence of the Tuscan ambassador, as a favor to the influential Grand Duke Ferdinand II de' Medici. When the ambassador reported Galileo's arrival and asked how long the proceedings would be, the Pope replied that the Holy Office proceeded slowly, and was still in the process of preparing for the formal proceedings. In the event, having responded to the urgent demands of the Inquisition that he must report to Rome immediately, Galileo was left to wait for two months before proceedings would begin.

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. The Inquisition questioned him on whether he had been ordered in 1616 not to teach Copernican ideas in any way (see above); he denied remembering any such order, and produced a letter from Bellarmine saying only that he was not to hold or defend those doctrines.

He was then detained for eighteen days in a room in the offices of the Inquisition (not in a dungeon cell). During this time the Commissary General of the Inquisition, Vincenzo (later Cardinal) Maculano, visited him for what amounted to plea bargaining, persuading Galileo to confess to having gone too far in writing the book. 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 May 10, he submitted his written defense, in which he defended himself against the charge of disobeying the Church's order, confessed to having erred through pride in writing the book, and asked for mercy in light of his age and ill health.

A month later (June 21), by order of the Pope, he was given an examination of intention, a formal process that involved showing the accused the instruments of torture. At this proceeding, he said, "I am here to obey, and have not held this [Copernican] opinion after the determination made, as I said."

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". Galileo was forced at this time to "abjure, curse and detest" his work and to promise to denounce others who held his prior viewpoint. Galileo did everything the church requested him to do, following (insofar as there is any evidence) the plea bargain of two months earlier; nonetheless, he was convicted of "grave suspicion of heresy" and was sentenced to life imprisonment.

Although ten Cardinal Inquisitors had heard the case, the sentence delivered on June 22 bears the signature of only seven; one of the three missing was Cardinal Barberini, the Pope's nephew. It is generally held that this indicates a refusal to endorse the sentence. The seven who signed, however, were those who were present at that day's proceedings; Cardinals Barberini and Borgia in particular, were attending an audience with the Pope on that day. Analysis of the Inquisition's records has shown that the presence of only seven of ten Cardinals was not exceptional; hence the inference that Barberini was protesting the decision may be doubted.

That the threat of torture and death Galileo was facing was a real one is widely, though not universally, accepted. Many point to the earlier Inquisitional trial against Giordano Bruno, who was burned at the stake in 1600 ostensibly for holding a naturalistic view of the Universe. However, Bruno denied the doctrine of the Trinity, the Incarnation and the immortality of the soul, among other heresies. He partially recanted his heretical beliefs during the investigation of his works, but returned to them before the investigation was completed. Heretics were never burned unless they recanted and subsequently returned to their heresies. Galileo was never convicted of heresy; even in the second trial, he was only "vehemently suspected of heresy".

It is often held that he was punished at the second trial for having disobeyed what was believed to be a valid injunction not to discuss Copernicanism. The formal decision of the court, however, makes no mention of such an order, condemning him only for the Copernican teachings. Moreover, in order to believe that there was such an injunction, one would have had to deny the word of a Cardinal (now a Saint) of the Church. In any case, such disobedience was not punishable by death. Thus, there is no substantial correspondence between Galileo's case and Bruno's. Whether such fine legal distinctions entered into Galileo's assessment of the dangers that faced him while the Inquisition was threatening him with torture and death is, of course, beyond the scope of this article.

The tale that Galileo, rising from his knees after recanting, said "E pur si muove!" (But it does move!) cannot be accepted as true: the penalty for going back on a confession before the Inquisition was to be burned at the stake (famously, in the case of Giordano Bruno and Jacques de Molay), and such a defiance would have been a ticket to follow Bruno to the stake. But the widespread belief that the whole incident is an 18th century invention is also false. (Drake, 1978, pp. 356–357). 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 "E pur si muove" was circulating in Galileo's time. In the months immediately after his condemnation, Galileo resided with Archbishop Ascanio Piccolomini of Siena, a learned man and a sympathetic host; the fact that Piccolomini's brother was a military attaché in Madrid, where the painting was made some years later, suggests that Galileo may have made the remark to the Archbishop, who then wrote to his family concerning the event, which later became garbled in re-telling.

Galileo in Arcetri

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. Because of a painful hernia, he requested permission to consult physicians in Florence, which was denied by Rome, which warned that further such requests would lead to imprisonment. Under arrest, he was forced to recite penitentiary psalms regularly, but his daughter, who was a nun at a nearby convent, successfully petitioned Rome to be allowed to say the psalms in his place. He was not supposed to have house guests, but this rule was not always strictly enforced. He was allowed to continue his less controversial research. During his confinement at home, Galilei managed write an important book on his discoveries in physics (not related to the astronomical controversies), the "Discorsi e Dimostrazioni Matematiche, intorno á due nuoue scienze" or Two New Sciences.

Publication was another matter. His Dialogue had been put on the Index Librorum Prohibitorum, the official black list of banned books, where it stayed until 1822 (Hellman, 1998). The banning of specific works was not an uncommon occurrence or one necessarily involving other dire consequences; Bellarmine himself had at one time been threatened with having his own work placed on the index. Nor, of course, did the ban inhibit Protestants and others; it meant only that Roman Catholics would not be able (without special permission) to know what Galileo had written. However, the prohibition did not stop at the one book. 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. The ban was effective in France, Poland, and German states, but not in the Netherlands. When the time came to publish the new book, Galileo had it smuggled out to Leiden, where it was published in 1638.

Placed under house-arrest, Galileo would, in 1638, be allowed to move to his home near Florence. Though by then totally blind, he continued to teach and write. After more than 8 years under arrest, he died at his villa in Arcetri, just north of Florence, in 1642.

According to Andrew Dickson White, in A History of the Warfare of Science with Theology in Christendom (III.iii), 1896, Galileo's experiences demonstrate a classic case of a scholar forced to recant a scientific insight because it offended powerful, conservative forces in society: for the church at the time, it was not the scientific method that should be used to find truth—especially in certain areas— but the doctrine as interpreted and defined by church scholars, and White documented how this doctrine was defended by the Church with torture, murder, deprivation of freedom, and censorship. In a less polemical frame, this has remained the mainstream view among the historians of science. However, this elides much of the underlying complexity of the trials and their context within Church and secular academic politics, as well as the weaknesses of some of Galileo's specific arguments, in light of the imprecise observations available at the time.

The viewpoints of White and similar-minded colleagues were never accepted by the Catholic community, partially because White's final analysis depicted Christianity as a destructive force. A fierce expression of this critical attitude can also be seen in Bertolt Brecht's play about Galileo, a source for popular ideas about the scientist. This is, of course, unfortunate. Brecht, a Marxist, was not interested in hewing to the historical facts so much as he was in making a case against theism and for atheism. Moreover, deeper examination of the primary sources for Galileo and his trial shows that claims of deprivation were likely exaggerated. Dava Sobel's biography 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 and 340 years after his death, Pope John Paul II established a commission that ultimately 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." After the release of this report, the Pope said further that "... Galileo, a sincere believer, showed himself to be more perceptive in this regard [the relation of scientific and Biblical truths] than the theologians who opposed him."

Galileo's family

Galileo's parents were were Vincenzo Galilei and Guilia Ammannati. Vincenzo, born in Florence in 1520, was a musician. Guilia, who was born in Pescia, married Vincenzo in 1563. Galileo was their first child. Although a devout Catholic, Galileo fathered three children out of wedlock. All were the children of Galileo and Marina Gamba. Because of their illegitimate birth, both girls were sent to the convent of San Matteo in Arcetri at early ages.

Virginia (b. 1600) who took the name Maria Celeste upon entering a convent. Galileo's eldest child, the most beloved, and inherited her father's sharp mind. She is buried with Galileo at the Basilica di Santa Croce di Firenze.

Livia (b. 1601) took the name Suor Arcangela. Was sickly for most of her life at the convent.

Vincenzio (b. 1606) was later legitimized and married Sestilia Bocchineri.

Galileo's writings

Two New Sciences 1638 Lowys Elzevir (Louis Elsevier) Leiden (in Italian, Discorsi e Dimostrazioni Matematiche, intorno á due nuoue scienze Leida, Appresso gli Elsevirii 1638)

Dialogue Concerning the Two Chief World Systems 1632 (in Italian, Dialogo dei due massimi sistemi del mondo)

The Starry Messenger 1610 Venice (in Latin, Sidereus Nuncius)

Letter to Grand Duchess Christina

Writings on Galileo

Galileo Galilei, an opera by Philip Glass

Galileo a play by Bertolt Brecht


  • Drake, Stillman (1957). Discoveries and Opinions of Galileo. New York: Doubleday & Company. ISBN 0-385-09239-3
  • Drake, Stillman (1973). "Galileo's Discovery of the Law of Free Fall". Scientific American v. 228, #5, pp. 84-92.
  • Drake, Stillman (1978). Galileo At Work. Chicago: University of Chicago Press. ISBN 0-226-16226-5
  • Fantoli, Annibale (2003). Galileo—For Copernicanism and the Church, third English edition. Vatican Observatory Publications. ISBN 88-209-7427-4
  • Fillmore, Charles (1931, 17th printing July 2004). Metaphysical Bible Dictionary. Unity Village, Missouri: Unity House. ISBN 0-871-59067-0
  • Hellman, Hal (1988). Great Feuds in Science. Ten of the Liveliest Disputes Ever. New York: Wiley.
  • Lessl, Thomas, "The Galileo Legend". New Oxford Review, 27-33 (June 2000).
  • Newall, Paula (2004). "The Galileo Affair."
  • Settle, Thomas B. (1961). "An Experiment in the History of Science". Science, 133:19-23.
  • Sobel, Dava. (1999). Galileo's Daughter. ISBN: 0-140-28055-3
  • White, Andrew Dickson (1898). A History of the Warfare of Science with Theology in Christendom. New York 1898.

Sculpture of Galileo

Galileo, Justus Susterman

Named after Galileo

The Galileo mission to Jupiter

The Galilean moons of Jupiter

Galileo Regio on Ganymede

Galilaei crater on the Moon

Galilaei crater on Mars

Asteroid 697 Galilea (named on the occasion of the 300th anniversary of the discovery of the Galilean moons)

Galileo (unit)

Galileo positioning system

See also

Galilean transformation
Galilean invariance
Lorentz transformation equations
Vincenzo Galilei
World Almanac's Ten Most Influential People of the Second Millennium


Note 1: Galileo, Lucid Cafe Feb '96"


Biographies of Physicists and Astronomers

Retrieved from ""
All text is available under the terms of the GNU Free Documentation License

Home - Hellenica World