Galileo Galilei

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Galileo Galilei - portrait of Domenico Tintoretto , ca.1602-1607Galileo's signature

Galileo Galilei (born February 15, 1564 in Pisa ; † December 29, 1641 July / January 8,  1642 greg. In Arcetri near Florence ) was an Italian polymath . He was a philosopher , mathematician , engineer , physicist , astronomer and cosmologist . Many of his discoveries, especially in mechanics and astronomy , are considered groundbreaking. He developed the method of exploring nature through a combination of experiments, measurements and mathematical analyzes, and thus became one of the most important founders of the modern exact natural sciences . He also became famous for the fact that the Catholic Church condemned him; In 1992 she rehabilitated him.

life and work

Origin and years of apprenticeship

Freeze frame; Uffizi Gallery , Florence

Galileo Galilei came from an impoverished Florentine patrician family . His family branch had taken the name of an important ancestor, the doctor Galileo Bonaiuti (15th century). Galileo's father Vincenzo was temporarily after his marriage to Giulia Ammannati (Pisa, 1562) cloth merchant, but otherwise a musician, composer and music theorist and had mathematical knowledge and interests; he lived permanently in Florence from the 1570s. There he examined, among other things, the sound of a vibrating string and discovered the quadratic relationship between the changes in tension or length of the string when the pitch should change by a certain interval .

Galileo was a novice in the convent of Vallambrosian educated and showed tendency in the Benedictine order to enter, but was brought by his father home and 1580 to study medicine to Pisa sent where Galileo enrolled in 1581; there was one of his lecturers Andrea Camuzio .

After four years, he abandoned his studies and went to Florence in Ostilio Ricci , a scholar of the school of Nicolo Tartaglia , mathematics study. He earned his living with private tuition, occupied himself with applied mathematics, mechanics and hydraulics and began to draw attention to himself in the educated circles of the city with lectures and manuscripts . Before the Accademia Fiorentina, he shone with a geometric-philological lecture on the topography of Dante's hell ( Due lezioni all'Accademia fiorentina circa la figura, sito e grandezza dell'Inferno di Dante, 1588). In 1585/86 he published the first results on the weight of solid bodies (theoremata circa centrum gravitatis solidorum) (in the tradition of Archimedes ' writing about it) and solved an ancient problem handed down in an anecdote about Archimedes (the crown of Hieron II ) by constructing a hydrostatic one Scales for determining the specific weight ( La bilancetta, manuscript). His application for a professorship in mathematics at the Pontifical University of Bologna in 1587 was unsuccessful, although he made himself three years older in the application. The older Giovanni Antonio Magini , who had also studied there, was preferred. The reviewers also suspected an error in the mathematical writings that Galileo included in the application. After that he established a reputation as a mathematician in Florence, among other things through public lectures at the academy on the architectural dimensions of hell (1588) and through a manuscript on the theory of the priorities in the tradition of Archimedes (1587), which he circulated let.

University professor in Pisa, 1589–1592

The candlestick in Pisa Cathedral , on which Galileo is said to have examined the pendulum laws

In 1589, Galileo received a post as a professor and chair of mathematics at the University of Pisa for three years . He taught Euclid's elements and elementary astronomy as well as astrology for medical professionals. The pay was low, however; nevertheless he managed to build and sell excellent instruments. He also developed a thermometer that was still very imprecise . He examined the pendulum motion and found that the period does not depend on the deflection or the weight of the pendulum, but on its length. Until the last years of his life he was concerned with the problem of how to use this discovery to construct a pendulum clock .

Starting from the movement of the pendulum, Galileo introduced the inclined plane with a subsequent horizontal path as an experimental arrangement to investigate the laws of fall . He experimented with balls made of different materials. This made it possible for the first time to give the slowly rolling balls a certain speed and to measure this. This is how he discovered acceleration and the fact that it is completely different from speed. This, in turn, can best be represented in the formula language of mathematics. Galileo formulated this new approach to physics most clearly in the Saggiatore in 1623 :

“La filosofia è scritta in questo grandissimo libro che continuamente ci sta aperto innanzi a gli tcchi (io dico l'universo), ma non si può intendere se prima non s'impara a intender la lingua, e conoscer i caratteri, ne 'quali è scritto. Egli è scritto in lingua matematica, ei caratteri son triangoli, cerchi, ed altre figure geometriche, senza i quali mezzi è impossibile a intenderne umanamente parola; senza questi è un aggirarsi vanamente per un oscuro laberinto. ”

“The philosophy is written in this great book, the universe that is always open to our gaze. But the book cannot be understood without first learning the language and familiarizing oneself with the letters in which it is written. It is written in the language of mathematics, and its letters are circles, triangles, and other geometrical figures without which it is impossible for man to understand a single word of it; without this one wanders around in a dark labyrinth. "

- Galileo Galilei : Il Saggiatore

Galileo's pupil and first biographer Vincenzo Viviani claimed that Galileo had also tried to fall from the Leaning Tower in Pisa . However, there is no reference to such attempts in Galileo's own writings and records. This is to be distinguished from the tower argument as a thought experiment , which Galileo deals with in his main work Dialogo .

Galileo summarized the results of his mechanical investigations in a manuscript which is now cited as De motu antiquiora and which was not printed until 1890. The attacks on Aristotle contained therein were unfriendly to his Aristotelian colleagues in Pisa. Galileo's employment was not extended in 1592. His material situation was further aggravated by the fact that his father had died in 1591 and, as the eldest son, he now had to take responsibility for his siblings (one brother and three sisters) and mother.

Professor in Padua, 1592-1610

Thanks to good protection, Galileo was appointed to the chair of mathematics at the University of Padua in 1592, which Giordano Bruno had hoped for. In Padua, which was part of the rich and liberal Republic of Venice , Galileo stayed for 18 years.

Although his position was much better paid than the previous one in Pisa, Galileo improved his salary by giving private tuition to distinguished students, including two later cardinals , in addition to his academic lectures . In addition, from 1597 Galileo sold a proportion circle . He employed his own mechanic to manufacture this forerunner of the slide rule , which was called Compasso and whose construction he had considerably improved. In a letter to Johannes Kepler this year he made it clear that he favored the heliocentric world system over the prevailing belief in the geocentric worldview : "... our teacher Copernicus , who was laughed at".

The supernova of 1604 , now named after Kepler, prompted him to give three public lectures in which he attacked Aristotelian astronomy and natural philosophy . From the fact that no parallax could be determined, Galileo concluded, as did Tycho Brahe in 1572 , that the new star was far from the earth and must therefore be in the fixed star sphere . According to the prevailing doctrine, this sphere was held to be unchangeable and Galileo thus represented a further argument against the views of the Peripatetics , as the Aristotle students were also called. He continued his investigations into the laws of motion during these years.

Pen and ink drawing from the Sidereus Nuncius and photo
Notes of Galileo on the discovery of the moons of Jupiter (1610)

In 1609 Galileo heard about the telescope, which had been invented by Jan Lippershey in Holland the year before . He built a device with about four times magnification from commercially available lenses , then learned to grind lenses himself and soon achieved eight to nine times, in later years up to 33 times magnification. A shopping list discovered in the National Library of Florence also dates from this period and gives an insight into how Galileo put his findings into practice.

On August 25, 1609, Galileo presented his instrument, the military use of which was obvious and which, in contrast to the Kepler telescope developed a little later, provided an upright image to the Venetian government - the Signoria. The instrument made a deep impression and Galileo left the Signoria the completely illusory sole right to manufacture such instruments, whereupon his salary was increased. Various claims have been made that Galileo claimed the invention of the telescope against his better judgment, for example by Brecht in the drama The Life of Galilei and by Hans Conrad Zander , who referred to the Galileo quotation on a "telescope he recently invented" from the Sidereus Nuncius calls. On the other hand, Galileo probably did not pass the basic idea of ​​the telescope off as his own invention, but a reduction in salary (suspension) in the following year indicates that the Signoria felt that she was being duped.

Galileo was one of the first people to use a telescope to observe the sky . This marked a revolution in astronomy , because until then people had to rely on observation with the naked eye . He found that the moon's surface was rough and uneven, with bumps, crevices and craters. He also recognized that the dark part of the moon's surface is lightened by the earth (so-called earth shine ) and that the planets - in contrast to the fixed stars - can be seen as disks. He discovered the four largest moons of Jupiter , which he called the Medici stars in preparation for his move to the Medici Court and which are now referred to as the Galilean moons . He observed that the Milky Way is not a foggy structure (as it appears to the naked eye), but rather "nihil aliud quam innumerarum Stellarum coacervatim consitarum congeries (nothing more than an accumulation of countless stars)". These discoveries and his pen drawing of the lunar surface were published in the Sidereus Nuncius (Star Messenger or Message from the Stars) of 1610 and made Galileo famous in one fell swoop. Although Galileo published a depiction of a clearly non-existent large moon crater at the terminator , the Sidereus Nuncius was sold out within a few days.

Court mathematician in Florence, from 1610

Galileo Galilei's desk in the recreated Galilei room in the Deutsches Museum in Munich.

In autumn 1610 the Grand Duke of Tuscany and former pupil of Galileo Cosimo II. De 'Medici appointed him court mathematician, court philosopher and the first mathematics professor in Pisa without any teaching obligation. Galileo was thus given full freedom to devote himself entirely to his research. As early as 1605, Galileo had been elected a member of the Florentine Accademia della Crusca , and after his move he also took on leadership roles in it. In 1658 the Academy decided to use his opera in the next edition of the Vocabolario (published in 1691) as one of the textual bases for mathematical and philosophical terminology.

At the latest when he moved to Florence, Galileo separated from Marina Gamba, his housekeeper, with whom he had three children: Virginia (religious name: Maria Celeste ; 1600–1634), Livia (religious name: Arcangela; 1601–1659) and Vincenzio (1606–1659) 1669). With the help of an admirer, Cardinal Maffeo Barberini and later Pope Urban VIII , Galileo put his daughters in a monastery before they reached the minimum age, because as illegitimate children they had little chance of a proper marriage. The son was sent to his father in Florence in 1613 after Marina Gamba married a man named Giovanni Bartoluzzi. Galileo later legitimized him.

More astronomical discoveries

Galileo continued his astronomical observations and found that the planet Venus shows phase shapes like the moon . He interpreted the Venus sickle and the fuller phases in such a way that Venus is sometimes between the sun and earth, but at other times beyond the sun. About this he corresponded with the Roman Jesuits around Christophorus Clavius ( with whom he had already had a controversial discussion in 1587), who had already discovered the phase shape of Venus independently of him. The Jesuit mathematician and the astronomer were more or less clear about the cosmological consequences and about the fact that the Ptolemaic worldview was no longer tenable .

In his enthusiasm for his scientific findings, he sent telescopes made in his workshop to friends and other scientists. However, only a few copies achieved the desired resolution . It could happen that some could not see the moons of Jupiter and others of his discoveries and assumed that he was intent on deception.

In 1611 Galileo visited Rome . He was highly honored for his discoveries and with his telescope he immediately made "le cose nuove del cielo" (the newly discovered objects in the sky) accessible to his friends - including the Jesuits: Jupiter with its four companions, the mountainous, rugged moon, the "horned", d. H. sickle-shaped Venus and the "triple" Saturn. He was then appointed sixth member of the Accademia dei Lincei . This honor was so important to him that from then on he called himself Galileo Galilei Linceo .

During this stay he had an audience with Pope Paul V and met his old admirer Maffeo Barberini. A year later, Barberini was there when Galileo refuted another, untenable claim by Aristotle with a simple but convincing experiment: Ice floats on water not because it is heavier but shallow, but because it is lighter.

Between the end of 1610 and mid-1611, Galileo first observed dark spots on the solar disk with a telescope. This discovery of the sunspots involved him in a dispute with the Jesuit Christoph Scheiner : There was a dispute about both priority and interpretation. In order to save the perfection of the sun, Scheiner assumed that the spots were satellites, whereas Galileo cited the observation that sunspots arise and disappear. He published this finding in 1613 in Lettere solari, one of the first scientific works that was not written in Latin but in colloquial language.

For Galileo it was obvious that his astronomical observations supported the heliocentric worldview of Nicolaus Copernicus , but did not provide any conclusive proof: All observations such as the phases of Venus were also compatible with the world model of Tycho Brahe , according to which the sun and moon surround the earth, the but rotate other planets around the sun. In fact, it was not until 1729 that James Bradley succeeded in using the stellar aberration to demonstrate the earth's proper motion in relation to the sphere of fixed stars.

Galileo initially held back in interpreting his astronomical observations. However, already during his time in Pisa the thought occurred to him that the rotations (revolutiones) of the earth around its axis and around the sun are the cause of the tides : "The waters would be accelerated and moved back and forth". He believed that he had proof of the Copernican view of the world. Only Isaac Newton was able to prove in 1687 that in addition to centrifugal force , the forces of attraction of the masses of the moon and sun are also responsible for ebb and flow .

Controversial discussions at the Florentine court prompted Galileo to declare that astronomical information in the Bible should not be taken literally, that a biblical interpretation compatible with the Copernican system was possible, and that research should be free from church doctrine (letter to his pupil and successor in Pisa, Benedetto Castelli , December 21, 1613, a copy of which was leaked to the Inquisition on February 7, 1615 by the Dominican Niccolò Lorini ). On February 16, 1615, Galileo sent a weakened, less heretical version of the letter as the alleged original to his friend Piero Dini in Rome with the request that it be circulated in the Vatican. Many copies were made of both versions and it was long unclear whether Galileo's claim to protection was correct. The original, provided by Galileo with numerous deletions and additions, which Castelli had sent back to him, was only rediscovered in the library of the Royal Society in summer 2018 ; it was missed in the catalog on October 21, 1613.

In March 1614 Galileo succeeded in determining the specific weight of air as one 660th of the weight of water - the prevailing opinion at the time was that air had no weight. This was another refutation of Aristotelian beliefs. During this time he was often active as an expert for the Grand Duke on technical and physical issues. As a researcher, he dealt in particular with hydrodynamics , light refraction in glass and water, and mechanics with the mathematical description of the acceleration of any body.

In the years 1610–1614 he stayed frequently on the estate of his friend Filippo Salviati in order to restore his health, which had been bad for years.

The process of 1616

In 1615, the cleric Paolo Antonio Foscarini (circa 1565-1616) published a book that was supposed to prove that Copernican astronomy did not contradict Scripture. Thereupon the Roman Inquisition opened an investigation procedure after preparatory work by the important Doctor of the Church, Cardinal Robert Bellarmin , a central figure of the Curia and the Inquisition. In 1616 Foscarini's book was banned. At the same time, some non-theological writings on Copernican astronomy, including a work by Johannes Kepler, were placed on the Librorum Prohibitorum index . The main work of Copernicus, De revolutionibus orbium coelestium , published in 1543, the year of his death, was not forbidden, but "suspended": From then on until 1822 it was only allowed to appear in the sphere of influence of the Roman Inquisition in arrangements that emphasized that the heliocentric system was a mere mathematical model.

Galileo was not officially involved in this process, which cannot be counted among the inquisition trials. However, his attitude was an open secret, even if the letter to the Grand Duchess mother had not yet been published. A few days after the formal resolution of the index, Bellarmine wrote a letter to Galileo with the assurance that Galileo had not had to renounce any teaching; At the same time, however, this letter contained the emphatic admonition not to defend the Copernican system as a fact in any way, but rather to discuss it as a hypothesis . This letter was cited as evidence of Galileo's disobedience in the 1632/33 trial. However, there were two different versions in the files, only one of which was correctly signed and delivered, which is why some historians in the 19th and 20th centuries assumed that the Inquisition Authority had forged evidence to the disadvantage of Galileo in 1632.

From then on Galileo held back from making public statements about the Copernican system. From 1616 he worked intensively on the possibility of using the movements of Jupiter's moons as a timekeeper to solve the longitude problem. However, he was unsuccessful. He also changed a telescope into a microscope for the first time , but without seriously pursuing the discoveries made with it.


Title page from Il Saggiatore, engraving by Francesco Villamena , 1623

In 1623 Galileo's old patron, Cardinal Maffeo Barberini, was elected Pope (Urban VIII). Galileo immediately dedicated his work Saggiatore (Italian = the gold balance), a polemic against the Jesuit priest Orazio Grassi about the comet appearances from 1618–1619, about atomistic and methodological questions. In this book, on which he had been working since 1620, Galileo expressed his now famous conviction that philosophy (according to the parlance of the time, this means natural science) is in the book of nature, and that this book is written in mathematical language: Without To master geometry , you don't understand a single word. Since then, Galileo has been considered the founder of the modern, mathematically oriented natural sciences, at the same time this contained a clear rejection of alchemy and astrology .

In the Saggiatore he resorted to Aristotle's theory of meteors and interpreted the comets as near-Earth optical effects, comparable to phenomena such as rainbows or polar lights . At the time of the comet's appearance, however, Galileo was unable to make observations himself for health reasons. His empirically unfounded polemics against the theory of comets, which Tycho Brahe and Orazio Grassi advocated, should be understood as an indirect defense of the Copernican system, which would have been threatened by the assumption that celestial bodies did not move on circular orbits.

The Saggiatore was reported anonymously for atomism and thus a violation of the dogmas of the Tridentine Council concerning the Eucharist . With the help of a courtesy report from Father Giovanni Guevara, Galileo's patrons in the Vatican had this advertisement panned out. The historian of science Pietro Redondi therefore suspects that the 1633 trial was also based on a complaint of atomism and thus heretical views regarding the Lord's Supper, which was diverted to the far less explosive question of Copernicanism and disobedience through the intervention of the specially created papal investigative commission.

The dialogue about the two world systems

Title page of Galileo's Dialogue: Aristotle, Ptolemy and Copernicus discuss.

In 1624 Galileo traveled to Rome and was received six times by Pope Urban VIII, who encouraged him to publish on the Copernican system as long as he treated it as a hypothesis ; Urban VIII did not know the letter from Bellarmine to Galileo from 1616 at that time.

After long preparatory work and again interrupted by illness, in 1630 Galileo completed the Dialogo di Galileo Galilei sopra i due Massimi Sistemi del Mondo Tolemaico e Copernicano (Dialogue of Galileo Galilei on the two most important world systems, the Ptolemaic and the Copernican). In this book, Galileo explained, among other things, his principle of relativity and his proposal for determining the speed of light . The first precise measurement of the speed of light on earth was not made until 1849 by Fizeau . As supposedly the strongest argument for the Copernican system, Galileo used his - erroneous - theory of the tides .

In May 1630, Galileo traveled again to Rome to obtain an imprimatur from Pope Urban VIII and the inquisitor Niccolò Riccardi, who was responsible for the censorship . He then received preliminary permission to print. Back in Florence, Galileo decided, for various reasons, to be content with the imprimatur by the Florentine Inquisitor and to have the work printed in Florence. Two of these reasons were the death of the editor, Prince Cesi, founder of the Accademia dei Lincei, and a plague epidemic. Due to various difficulties caused by Riccardi, however, printing could not begin until July 1631. The Dialogo appeared in February 1632 . Galileo Galilei dedicated the book to Grand Duke Ferdinando II de 'Medici and handed him the first printed copy on February 22nd.

In two respects, the Dialogo set new accents in the current, astronomical and also ideological-theological discourse:

  1. The vernacular Italian took the place of the scientific language of Latin , because the discussions should be carried out specifically beyond the scientific circles.
  2. He deliberately kept silent about the Jesuits - u. a. Clavius, Giovanni Riccioli , Grimaldi - favored Tychonic planetary models . Analogous to Copernicus' model, it would have explained some phenomena such as the occasional Venus sickle and the variable size of the planetary disks . In the struggle for the interpretive sovereignty of the astronomical worldview, Galileo fought the competitor Tycho Brahe with dead silence.

The censorship requirement to conclude the work with a closing speech in favor of the Ptolemaic system, Galileo thought to comply with by putting this speech into the mouth of the obvious fool Simplicio . Moreover, he made the mistake of making fun of a favorite thought of Barberini (Urban VIII.): That one could never test a theory about the effects it had predicted, since God could produce these effects at any time in other ways. With that, Galileo had gone too far and gambled away the protection of the Pope.

The trial against the dialogue

Galileo Galilei - Portrait of Justus Sustermans (1636)

In July 1632 Riccardi instructed the Inquisitor of Florence to prevent the dialogue from spreading . In September the Pope called Galileo to Rome. With a request for postponement, medical certificates, a lengthy journey and, on top of that, quarantine due to the plague epidemic, the entire winter passed.

In Rome, Galileo lived in the residence of the Tuscan ambassador. At the beginning of April 1633 he was officially questioned and had to move into Inquisition accommodation for 22 days. On April 30th, in a second hearing, he confessed that he had made a mistake in his book and was allowed to return to the Tuscan embassy.

On May 10th, he submitted his written defense, asking for mercy. On June 22nd, 1633 the trial took place in the Dominican monastery next to the basilica of Santa Maria sopra Minerva . At first Galileo, referring to the dialogue form of his work, denied having taught the Copernican system.

The Bellarmine Letter (which version is not known) was shown to him and he was accused of disobedience. After renouncing, cursing and loathing his mistakes, he was sentenced to life imprisonment and escaped execution at the stake.

That Galileo was condemned at all was a matter of dispute among the ten cardinals responsible; three of them (including Francesco Barberini , the Pope's nephew) did not sign the judgment.

Galileo himself held fast to his convictions. The claim that he is said to have mumbled, "Eppur si muove" (and it [the earth] does move) as he left the courtroom, is often considered an afterthought. It was spread soon after his death, as shown by a Spanish painting from around 1643/45 with these words, which was discovered in 1911.

Galileo saw circular orbits as a central component of the Copernican system and rejected elliptical orbits for this reason. With his model of the elliptical orbits, Kepler, with whom he was in correspondence, had practically eliminated all inconsistencies between observation and the heliocentric worldview. To save his concept of circular orbits, Galileo accepted that it predicted the observed position of the planet Mars much worse than the geocentric models of Ptolemy or Brahe.

The fact that Galileo reinterpreted the comets as atmospheric phenomena because the alternative explanation of objects moving around in the solar system would have endangered his view of the world would also have been rather detrimental to the credibility of his model. In the case of sunspots, which can only be observed with great danger to the eyesight, the number of sunspots decreased after 1610 and from 1645 onwards they remained almost completely absent for almost 75 years (so-called Maund minimum ).

Finally, in his dialogue, Galileo wisely discussed only the two world systems of Copernicus and Ptolemy. He had empirically refuted the latter based on the phases of Venus, but not Brahe's geocentric model, which was also compatible with his observations.

House arrest 1633–1642 and the Discorsi

After the judgment, Galileo remained under arrest in the embassy of the Duchy of Tuscany in Rome. After a few weeks he was placed under the supervision of the Archbishop of Siena , who, however, was his ardent admirer and supported him as much as he could. In Siena he was able to overcome his deep depression about the trial and its outcome.

After five months, in December 1633, he was allowed to return to his Villa Gioiella in Arcetri, but remained under house arrest, combined with the prohibition of any teaching activity. When he asked for permission to see doctors in Florence because of a painful hernia, his request was turned down with warnings that further such requests would lead to the release of house arrest and incarceration.

According to the judgment, he had to pray the seven penitential psalms weekly for over three years; his daughter, Sister Maria Celeste, assumed this responsibility while she was still alive. In addition, his social contacts were severely restricted. At least he was allowed to continue his less controversial research and visit his daughters in the monastery of San Matteo. All publications were forbidden to him, but he conducted an extensive correspondence with friends and scholars at home and abroad and was later able to receive temporary visitors, including Thomas Hobbes and John Milton , from 1641 his former student Benedetto Castelli .

Galileo had had problems with his eyes for a long time; In 1638 he became completely blind - be it as a result of his initially without adequate protection undertaken sun observations or due to a genetic predisposition. However, shortly before he completely lost his eyesight, he discovered the libration of the moon. A pardon for release was denied. He spent his last years in his country house in Arcetri.

Tomb of Galileo, Santa Croce , Florence

From July 1633 - while still in Siena - Galileo had been working on his main physical work Discorsi e Dimostrazioni Matematiche intorno a due nuove scienze . Although the Inquisition judgment did not contain an explicit publication ban, publication in the sphere of influence of the Catholic Church turned out to be impossible. It so happened that the world first became aware of Galileo's work through Matthias Bernegger's Latin translation, published under the title Systema cosmicum by Elsevier and printed in Strasbourg in 1635 by David Hautt. A print of the Italian text of the Discorsi was published by Elsevier in Leiden in 1638 .

In terms of content, Galileo took up approaches and results from his early years in the Discorsi. The two new sciences that Galileo founded in it are, in modern language, strength theory and kinematics . Among other things, he demonstrated that the arched movement of a projectile consists of two components: the horizontal with constant speed due to inertia , the downward with time-proportional increasing speed due to constant acceleration. The interaction of both leads to a parabolic trajectory. The book also contains a paradox about the infinite ( Galileo's paradox ), the underlying ideas of which were only developed by Georg Cantor much later in the 19th century .

In the late autumn of 1641 Evangelista Torricelli replaced the companion Vincenzo Viviani, who had been working for Galileo since 1639, as assistant and private secretary, but it was already clear that Galileo would not have long to live. He died on January 8, 1642 in Arcetri. A solemn burial in a splendid grave that the Grand Duke had planned was prevented. He was initially buried anonymously in Santa Croce in Florence. Only about 30 years later was the grave marked with an inscription. The representative tomb in Santa Croce that exists today was completed in 1737. It was financed by a foundation of the Galileo assistant Vincenzo Viviani .

Galileo and the Church

After the popes and cardinals had only just succeeded in consolidating their influence in Italy in the fight against the Reformation with the help of the Dominican and Jesuit orders, they interpreted the promotion of science in Great Britain, Holland and Germany as an ongoing attack on the declaratory sovereignty of their institutions - of the decreed consensus patrum . They found themselves compelled to insist on the traditional. At the same time, there were powerful ecclesiastical voices who rejected a literal interpretation of the Holy Scriptures and aggressively defended the argument that faith and science were separate spheres. Cardinal Bellarmine wrote that if there was real evidence of the heliocentric system, one would indeed have to be careful in interpreting the scriptures . An expression of the church's ambivalence towards him is the rather mild admonition of 1616 that Galileo was “in error of faith” and should therefore “refrain from spreading the Copernican view of the world”.

Galileo Galilei before the Inquisition in the Vatican 1632 - painting by Joseph Nicolas Robert-Fleury from 1847

Only after Galileo in 1632 with the Dialogo again advocated the Copernican view of the world and the first copies even to his declared opponents such as B. sent the Inquisitor Serristori, formal proceedings were opened against him. Even now, compared with other heresy trials, the climate was friendly and the judgment mild. After Galileo had sworn to have “always believed, to believe in the present and to want to believe in the future with God's help everything that the Catholic and Apostolic Church considers to be true, preaches and teaches”, he received only imprisonment, which after a few Weeks into house arrest. Galileo never sat in a dungeon.

The tragedy of Galileo's work lies in the fact that, as a lifelong deeply believing member of the Church, he attempted to save this Church from a fatal error. It was not his intention to refute or to divide the church, but rather to reform the worldview of the church. His various stays in Rome up to 1616 also had the purpose of convincing churchmen like Bellarmine that the Peripatetics were not infallible and that statements of astronomical content in the Holy Scriptures do not always have to be read to the letter. Galileo was also convinced that sooner or later he would be able to fully clarify the works of God through experiment and logic. Pope Urban VIII, on the other hand, took the view that the diverse natural phenomena caused by God were forever withdrawn from man's limited understanding.

The inquisition trial against Galileo sparked endless historical controversies and numerous literary adaptations; among others in Bertolt Brecht's Life of Galileo .

1741 granted the Roman Inquisition at the request of Benedict XIV. The imprimatur to the first edition of the works of Galileo. Under Pius VII. , In 1822, an imprimatur was first issued on a book that treated the Copernican system as a physical reality. The author, a certain Settele, was a canon . The interdict had long since become irrelevant to non-clerics.

In 1979, John Paul II commissioned the Pontifical Academy of Sciences to deal with the famous case. The commission report was delivered on October 31, 1992, and John Paul II gave a speech in which he presented his view of the relationship between church teaching and science. On November 2, 1992, Galileo Galilei was formally rehabilitated by the Roman Catholic Church . He should get a statue in the Vatican . In November 2008 the Vatican again distanced itself from the condemnation of Galileo by the papal inquisition. The then Pope Urban VIII did not sign the judgment against Galileo, the Pope and Curia did not stand united behind the Inquisition.

Scientific achievements

Founder of the scientific method

Galileo is considered to be the essential founder of modern natural sciences . On the one hand, he largely developed the method that was fundamental to them, consisting of the combination of his own observation, possibly based on planned experiments, with the most accurate quantitative measurement of the observable quantities and the analysis of the measurement results using the means of mathematics. On the other hand, he called for the results obtained in this way to be given priority over purely philosophical or theologically based statements about nature.

It was inevitable that Galileo, as the essential founder of the experimental methodology, was accused of never having carried out some of the experiments he described and given as proof of the correctness of his theories himself. This is considered to be refuted in essential points (see Fraud and Forgery in Science ).

Accelerated movement, principle of relativity and principle of inertia

One of Galileo's great conceptual achievements was the refutation of Aristotle's theory of motion, in particular the fundamental contradictions it formulated between rest and motion and between natural and unnatural (or forced) motion. Galileo measured the increase in the speed of fall on the inclined plane for the first time and found that it does not increase in discrete degrees and not in proportion to the distance traveled, but that it steadily increases in proportion to the elapsed time from zero and until the final speed is reached runs through all values ​​in between. The fact, observed by Johannes Buridan and Francis Bacon , that the purely mechanical processes such as falling and collision take place on an evenly moving ship in exactly the same way as on land, was generalized by Galileo to a new principle of relativity : According to this, there is no absolute difference between rest in the observable processes and (uniform) movement. This led him further to the establishment of the principle of inertia , because if the uniform movement of a body with a ship can just as well be viewed as rest by a passenger of the ship, then the maintenance of this movement obviously does not require any permanent external force . (P. 65), (chap. 7), (chap.1.4)


David Randolph Scott , Commander of the Apollo 15 lunar mission (1971), demonstrates Galileo's
law of fall, using a spring and a hammer that he drops in a vacuum on the moon , that all bodies fall at the same speed, regardless of their mass.

The steadily accelerated movement occupied Galileo for over forty years. His experimental innovation consisted in the use of a gutter as an inclined plane with which he could study the laws of fall on a decelerated timescale. He determined the acceleration by his pulse, with water clocks or by the fact that the body triggers a rhythmic signal when the trigger is placed at suitable intervals. Equally important for the development of the physical method was Galileo's step to use the knowledge gained from experiments to plan and carry out further experiments: With the help of the inclined plane, he prepared bodies that had a defined horizontal speed and was able to carry out the experiments with them make a horizontal throw.

The widespread story about Galileo's hand-carried drop tests from the Leaning Tower in Pisa can be classified as legend, because there is no reliable evidence for it. Likewise, it was and still is occasionally doubted that Galileo really carried out the attempts at accelerated movement on the inclined plane. The reason was originally based on the fact that in the entire estate of Galileo, which was published at the beginning of the 20th century, there were almost no records of measurements taken. However, in the 1960s Stillman Drake found numerous sheets by Galileo's hand after he himself had gone down to the archive in Florence, which had been left out of the complete edition. It was the logs of the measurements that had been considered unimportant when compiling the complete edition because there was little or no text on them, but sketches and numbers.

Strength theory

As is evident from the title of the Discorsi , Galileo published his results on the strength of a beam with the full awareness that it was the basis for a new science. The further development has proven him right; his contribution can actually be regarded as the foundation of the strength theory .

Galileo found that the load-bearing capacity of a beam is greater if it is placed upright, not flat. He was the first to put external stress in relation to internal tensions. However, he has not yet been able to develop a quantitative theory. He arranged the area of ​​vanishing tensile or compressive stress , known today as the neutral surface , at the lower edge of the clamped beam instead of in the middle of the beam cross-section. Corrections to this error could not prevail in the 17th and 18th centuries; it was not until the beginning of the 19th century that Navier successfully made a correction.


Galileo's astronomical discoveries are already listed in the biographical section. Some of them produced groundbreaking discoveries :

  • Supernovae do not take place sublunar , but far away: The fixed star sphere is not immutable.
  • The surface of the moon is rough and the sun shows spots : bodies in the sky are not perfect.
  • Jupiter orbits four moons : There are neither impenetrable, crystalline celestial spheres , nor does the aether turn around the earth in an eternal circle .
  • The Venus shows phases : It must therefore around the sun does not revolve around the Earth.

More inventions

Galileo's thermoscope from 1592 is the first detectable temperature measuring device . It was marked with graduation marks by Santorius and finally improved decisively by Fahrenheit in 1714.

Christiaan Huygens later developed Galileo's idea of ​​controlling a mechanical clock with a pendulum to make it ready for practical use.


Galileo Galilei on the Italian 2000 lire banknote
Postage stamp, Soviet Union 1964

See also category: Galileo Galilei as namesake .

Named after Galileo are:


  • Bertolt Brecht : Life of Galileo . (Denmark, 1938/39) Suhrkamp, ​​Frankfurt am Main 2002, ISBN 3-518-10001-7 .
    In the 8th picture, Galileo sums up the problem of scientific research and theological sovereignty of interpretation with a famous aperçu : "The sum of the angles in the triangle cannot be changed according to the needs of the Curia."
  • Zsolt Harsányi : And yet it moves. Translated from the Hungarian by Joseph P. Toth, Artur Luther. Esche Verlag, Leipzig 1937 (Pabel-Moewig Verlag, 1993, ISBN 3-8118-7557-4 ).
  • Atle Næss : When the world stood still: Galileo Galilei - betrayed, misunderstood, adored. Springer 2006.
  • Dava Sobel : Galileo's Daughter: A Story of Science, the Stars and Love. Berlin Verlag 2008 (first as Galileo's Daughter 1999).


  • Haggard : Eppur Si Muove. Concept album about Galileo Galilei, 2004, Metal. "Eppur Si Muove" means in German "and she (the earth) is moving".
  • Philip Glass : Galileo Galilei. 2001, opera.


Sculpture Galileo in Berlin


  • In 1947 Ruth Berlau and Joseph Losey filmed the Broadway production of Brecht's Life of Galileo with Charles Laughton in the title role. It is a black and white silent film of 30 minutes.
  • Ernst Schröder played Galileo in a German television adaptation based on Brecht's Life of Galileo , directed by Egon Monk . With a game length of 150 minutes, this is the longest implementation of the material on television so far.
  • In the 76-minute American television adaptation Lamp at Midnight (1966), which is not based on Brecht, Galileo was played by Melvyn Douglas .
  • In 1975 Joseph Losey directed Galileo (USA), a feature film based on Brecht's play. Chaim Topol played the scholar in the 145-minute Eastmancolor film.
  • In 1989, the director filmed Ivo Barnabò Micheli under the title "Eppur si muove" Galileo Galilei process their own research on the Inquisition trial of Galileo. In the film, Mario Adorf embodies both the figure of the contemporary researcher and that of the historical Galileo in a double role. In interviews u. a. the then Cardinal Joseph Ratzinger and the physicist Carl Friedrich von Weizsäcker have their say.



Galileo published his scientific findings in the following major works:

  • Sidereus Nuncius . Venice 1610. (German: News of New Stars )
  • Il Saggiatore. Rome 1623. (German: The examiner with the gold balance )
  • Dialogo sopra i due massimi sistemi. Florence 1632. German: Dialogue about the two main world systems. Leipzig 1891.
  • Discorsi e dimostrazioni matematiche. Leiden 1638. German: Discussion and mathematical demonstration about two new branches of knowledge concerning mechanics and the laws of fall. Leipzig 1890.

Newer editions are:

  • Edward Stafford Carlos (Ed.): The sidereal messenger of Galileo Galilei and a part of the preface to Kepler's Dioptrics containing the original account of Galileo's astronomical discoveries. London 1880,
  • Arthur von Oettingen (Ed.): Discussion and mathematical demonstration about two new branches of knowledge concerning mechanics and the laws of fall. Leipzig: Engelmann 1890,
  • Antonio Favaro (ed.): Le opere di Galileo Galilei. 20 volumes, Florence 1890 to 1909, reprints with additions Florence 1929 to 1939, 1964/1965.
  • Emil Strauss (transl., Ed.): Dialogue about the two main world systems. Teubner 1891,
  • Stillman Drake (Ed.): Discoveries and Opinions of Galileo. Doubleday & Company, New York NY 1957 (selection from his writings).
  • Stillman Drake (translator): On Mechanics. University of Wisconsin Press, Madison 1960.
  • Stillman Drake (translator): Il Saggiatore, The Assayer. In: Stillman Drake, Charles D. O'Malley (eds.): The Controversy of the Comets of 1618. The University of Pennsylvania Press, Philadelphia 1960.
  • IE Drabkin (transl.): On Motion. University of Wisconsin Press, Madison 1960.
  • Franz Brunetti (Ed.): Opere di Galileo Galilei. 2 volumes, Turin 1964.
  • Pio Paschini, Edmondo Lamalle: Vita e Opere di Galileo Galilei. 3 volumes, Vatican City 1964.
  • Hans Blumenberg (Ed.): Sidereus Nuncius. News of new stars. Suhrkamp Taschenbuch Wissenschaft 1980, 2002.
  • Galileo Galilei, Anna Mudry (Ed.): Writings, letters, documents. Albus im VMA-Verlag, Munich 1987, Wiesbaden 2005, ISBN 3-928127-94-2 .
  • Stillman Drake (translator, ed.): (Discourses on the) Two New Sciences. University of Wisconsin Press, Madison 1974, 2nd edition 1989, Toronto 2000.
  • Dialogue on the two main world systems. Marix Verlag, Wiesbaden 2014.
  • Ed Dellian (translator, ed.): Discorsi: Conversations and mathematical reasoning for two new areas of knowledge. Philosophical Library, Felix Meiner Verlag, 2015.


Individual aspects

  • Hans Bieri: The dispute over the Copernican world system in the 17th century. Galileo Galileo's theory of accommodation and its historical background. Bern 2007 Explains Galileo's methodological proposal for a biblical exegesis, which understands the texts as adapted to human comprehension possibilities and the underlying traditions; with text edition and commentary.
  • Horst Bredekamp : Galileo's thinking hand. Form and research around 1600. de Gruyter, Boston a. a. 2015, ISBN 3-11-041457-0 .
  • David Freedberg : The Eye of the Lynx. Galileo, his friends and the beginning of modern natural history. University of Chicago Press, Chicago Ill. 2002, ISBN 0-226-26147-6 .
  • Karl von Gebler : Galileo Galilei and the Roman Curia. Cotta, Stuttgart 1876,
  • Alexandre Koyré : Leonardo, Galilei, Pascal. The beginnings of modern science (= Fischer 13776). Fischer-Taschenbuch-Verlag, Frankfurt am Main 1998.
  • Alexandre Koyré: Études galiléennes. 3 volumes. Hermann, Paris 1939, 2nd edition in one volume, 1966.
  • Lydia La Dous: Galileo Galilei. To the story of a case. Pustet, Regensburg 2007, ISBN 978-3-7867-8613-9 (on the proceedings against Galileo).
  • Erwin Panofsky : Galileo Galilei and the visual arts. Presented by Horst Bredekamp, ​​translated from the English by Heinz Jatho. Diaphanes, Zurich 2012, ISBN 978-3-03734-149-0 .
  • Pietro Redondi : Galileo - the heretic. Munich 1989, ISBN 3-406-33981-6 (representation of the inquisition process of 1633, with some documents published for the first time).
  • Volker Remmert : Dedication, explanation of the world and legitimation of science. Cover pictures and their functions in the scientific revolution (= Wolfenbütteler Forschungen. Volume 110). Harrassowitz, Wiesbaden 2005, ISBN 3-447-05337-2 . In it especially the chapter on Catholic Bible Exegesis and the roots of the Galileo Affair. The copper title of the Opera mathematica (1612) by Christoph Clavius. Pp. 23-53.
  • Franz Heinrich Reusch : The process of Galileo and the Jesuits. Eduard Weber's Verlag, Bonn 1879,
  • Michael Segre, Eberhard Knobloch (ed.): The untamed Galilei. Steiner Verlag, 2001.
  • Galileo and the experiment. Practice of Natural Sciences / Physics, Volume 56, 2007.
  • István Szabó : History of mechanical principles and their main applications. Birkhäuser, 1979, ISBN 3-7643-1735-3 .
  • Karl-Eugen Kurrer : The History of the Theory of Structures. Searching for Equilibrium , Ernst & Sohn 2018, ISBN 978-3-433-03229-9 .

Popular science books on the astronomical environment

Web links

Wikisource: Galileo Galilei  - Sources and full texts (Italian)
Wikisource: Galileo Galilei  - Sources and full texts
Commons : Galileo Galilei  - album with pictures, videos and audio files

Overview pages

Primary texts

View of the Catholic Church

Individual evidence

  1. Heilbron, Galileo, Oxford UP 2010, p. 8.
  2. ^ After Franz Brunetti (ed.): Galilei, Opere . Volume 1. Turin, 1964, p. 44, lettore di matematica, initially appointed for three years. He held the chair of mathematics, which is why he is often referred to in literature as a professor in Pisa, z. B. in the article on Galileo in the Dictionary of Scientific Biography or Heilbron: Galilei . 2010, p. 41.
  3. Heilbron: Galileo . 2010, p. 46.
  4. ^ Opere di Galileo Galilei, Volume VI. G. Barbèra, Florenz 1933, p. 232 ( online ).
  5. ^ Galilei, Opere, Turin 1964, Volume 1, p. 44.
  6. Peter Prantner: The shopping list of Galileo Galilei. In: February 15, 2014, accessed February 16, 2014 .
  7. Hans Conrad Zander: Why the Inquisition was right in the Galileo case. In: The world. January 18, 2008, online version.
  8. See the essay by Horst Bredekamp, ​​Angela Fischel, Birgit Schneider, Gabriele Werner: Bildwelten des Wissens. ( Memento of May 24, 2013 in the Internet Archive ) (PDF; 1.6 MB).
  9. Das Labor nach Galilei , Deutsches Museum , Munich, accessed on July 25, 2017.
  10. ↑ List of members of the Crusca with a picture from the holdings of the Academy.
  11. ^ Text archive - Internet Archive
  12. Salvatore Ricciardo, Franco Giudice, Michele Camerota: Notes and Records , 2018, in press.
  13. Alison Abbott: Discovery of Galileo's long-lost letter shows he edited his heretical ideas to fool the Inquisition. nature news, 2018, doi: 10.1038 / d41586-018-06769-4 .
  14. Sources on the date of publication of the "Dialogo".
  15. Winfried Hofmann (arrangement): Winged words . The classic encyclopedia of quotations. 39th edition, Frankfurt am Main, Berlin 1993, p. 346 f.
  16. ^ Stillman Drake: Galileo at Work. His Scientific Biography. University of Chicago Press, Chicago 1978, p. 357.
  17. See Peter G. Watson: The Enigma of Galileo's Eyesight. Some Novel Observations on Galileo Galilei's Vision and His Progression to Blindness. In: Survey of Ophthalmology. Vol. 54, No. 5 (Sep./Oct. 2009), pp. 630-640, abstract .
  18. walwyn: Tomb of Galileo Galilei - Santa Croce Florence. In: Moriarty. October 27, 2012, accessed November 15, 2015 .
  19. Bellarmin's letter of April 12, 1615 to Foscarini. In: Anna Mudry (Ed.): Galileo Galilei: Writings - Letters - Documents. Volume 2, Beck, Munich 1987, ISBN 3-928127-94-2 , p. 47.
  20. ^ Walter Brandmüller: Galileo and the Church or The Right to Error. Pustet Verlag, Regensburg 1982, ISBN 3-7917-0743-4 .
  21. ^ Albrecht Fölsing: Galileo Galilei: A process without end. Rowohlt Taschenbuch Verlag, Reinbek near Hamburg 1996, ISBN 3-499-60118-4 .
  22. Matthias Dorn: The problem of the autonomy of the natural sciences in Galileo. Verlag Franz Steiner, Stuttgart 2000, ISBN 3-515-07127-X , p. 75 f.
  23. Peter Markl: It is enough for the mathematician. In: Wiener Zeitung . June 11, 1999, accessed November 19, 2013.
  24. Address of John Paul II to the participants in the plenary assembly of the Pontifical Academy of Sciences on October 31, 1992 . At: Retrieved February 5, 2010.
  25. ^ Vatican erects a monument to Galileo Galilei. On: Spiegel online. March 9, 2008.
  26. From Religion and Society. In: DLF. Nov 28, 2008. (News in the "Day by Day" series), 9:45 am.
  27. Ueli Niederer: Galileo Galilei and the development of physics . In: Quarterly publication of the Natural Research Society in Zurich . tape 127 , no. 3 , 1982, pp. 205–229 ( online (PDF) [accessed March 6, 2016]).
  28. Stillman Drake: Galileo . Herder, Freiburg 1999.
  29. ^ Julian B. Barbour: Absolute or Relative Motion? Cambridge University Press, Cambridge (GB) 1999.
  30. ^ Roberto Torretti: The Philosophy of Physics . Cambridge University Press, Cambridge 1999.
  31. Alexandre Koyré : Études galiléennes. (3 vols.) . Hermann, Paris 1939.
  32. ^ Stillman Drake : Galileo At Work. His Scientific Biography . University of Chicago Press, Chicago 1978, ISBN 0-226-16226-5 .
  33. Made accessible in digitized form by the National Library in Florence and the Max Planck Institute for the History of Science , e.g. B. .
  34. MARS, GALILAEI. ( Memento of May 10, 2010 in the Internet Archive ). In: Mars Gazetteer. National Science Space Data Center. Retrieved April 4, 2010.
    Planetary Map Index . In: USGS Astrogeology Science Center. Retrieved April 4, 2010.
  35. Lotte Burkhardt: Directory of eponymous plant names - Extended Edition. Part I and II. Botanic Garden and Botanical Museum Berlin , Freie Universität Berlin , Berlin 2018, ISBN 978-3-946292-26-5 doi: 10.3372 / epolist2018 .
  36. Life of Galileo (1962) in the Internet Movie Database (English)
  37. Lamp at Midnight (1966) in the Internet Movie Database (English)
  38. Galileo (1975) in the Internet Movie Database (English)
  39. Joachim Gatterer, Jessica Alexandra Micheli (ed.): Ivo Barnabò Micheli. Poetry of opposites. Cinema radicale. Folio-Verlag, Vienna / Bozen 2015, pp. 90–100.
This article was added to the list of excellent articles on June 10, 2004 in this version .