Galileo Galilei was born in Pisa on February 15, 1564. The little that, through some letters, is known of his mother, Giulia Ammannati di Pescia, does not make her an overly flattering figure. His father, Vincenzo Galilei, was a Florentine and came from a family that had long been illustrious; A musician by vocation, economic difficulties had forced him to dedicate himself to commerce, a profession that led him to settle in Pisa.
A man of wide humanistic culture, he was an accomplished performer and a composer and music theorist, whose works on the subject enjoyed a certain fame at the time. From him Galileo had to inherit not only a taste for music (he played the lute), but also his independent character and fighting spirit, and perhaps even contempt for blind trust in authority and a taste for combining theory with practice.
Galileo was the first-born of seven brothers of whom three (Virginia, Michelangelo and Livia) had to contribute, over time, to increase their economic problems. In 1574 the family moved to Florence, and Galileo was sent as a student or perhaps as a novice to the monastery of Santa Maria di Vallombrosa for a while.
In 1581 Galileo entered the University of Pisa, where he enrolled as a medical student at the will of his father. Four years later, however, he dropped out of college without obtaining a degree, albeit with a good knowledge of Aristotle. Meanwhile, a decisive event had occurred in his life: his initiation in mathematics, apart from his university studies, and the consequent loss of interest in his career as a doctor.
Back in Florence in 1585, Galileo spent a few years devoted to the study of mathematics, although he was also interested in philosophy and literature (in which he showed his preferences for Ariosto over Tasso); His first work on the barycenter of bodies dates from that time – which he would later recover, in 1638.
After giving some private math classes in Florence and Siena, he tried to get regular employment at the universities of Bologna, Padua and in Florence itself. In 1589 he finally got a place in the Pisa Study, where his dissatisfaction with the impoverished salary received could not be less than manifested in a satirical poem against academic dress. In Pisa Galileo composed a text on movement, which he kept unpublished, in which, still within the framework of medieval mechanics, he criticized Aristotelian explanations for the fall of bodies and the movement of projectiles; in continuity with that criticism.
In 1591 the death of his father meant for Galileo the obligation to take responsibility for his family and attend to the dowry of his sister Virginia. Thus began a series of economic difficulties that would only worsen in the following years; in 1601 he had to provide for the dowry of his sister Livia without the collaboration of his brother Michelangelo, who had gone to Poland with money that Galileo had lent him and that he never returned (on the contrary, he later settled in Germany, thanks again to the aid of his brother, and then sent his whole family to live with him).
The need for money at that time was increased by the birth of Galileo’s own three children: Virginia (1600), Livia (1601) and Vincenzo (1606), due to his union with Marina Gamba, which lasted from 1599 to 1610. and who did not marry. All this made insufficient the small improvement achieved by Galileo in his remuneration when he was chosen, in 1592, for the chair of mathematics at the University of Padua by the Venetian authorities who ran it. He had to resort to private classes, advances and even loans. Despite everything, Galileo’s stay in Padua, which lasted until 1610, was the most creative, intense and even happy period of his life.
In Padua Galileo had the opportunity to deal with technical issues such as military architecture, castration, topography and other related subjects that he discussed in his private classes. Various inventions also date back to that time, such as a water-lifting machine, a thermoscope and a mechanical calculation procedure that he exhibited in his first printed work: Le operazioni del compasso geometrico e militare, 1606.
Originally designed to solve a problem An artillery pilot, the instrument was soon refined by Galileo, who expanded its use in solving many other problems. The usefulness of the device, at a time when logarithms had not yet been introduced, enabled it to earn some revenue through its manufacturing and marketing.
In 1602 Galileo resumed his movement studies, experimenting with the pendulum isochronism and movement along an inclined plane to decide what the bass drop rule was. From then, and until 1609, when he formed the ideas that would form the core of his Discorsi thirty years later.
The stars’ message
In July 1609, on a visit to Venice (to request a raise), Galileo learned of a new optical instrument that a Dutchman had presented to Prince Maurice of Nassau; It was the telescope, the practical importance of which Galileo immediately grasped, dedicating his efforts to improving it until it became a true telescope. Although he declared that he had managed to perfect the apparatus thanks to theoretical considerations on the optical principles that were its foundation, most likely, he did so by means of successive practical attempts that, at most, were supported by some very summary reasoning.
Be that as it may, his undeniable merit lay in the fact that he was the first to succeed in extracting a decisive scientific advantage from the apparatus. Indeed, between December 1609 and January 1610 Galileo made the first observations of the Moon with his telescope, interpreting what he saw as evidence of the existence on our satellite of mountains and craters that demonstrated their community of nature with Earth; the traditional Aristotelian theses about the perfection of the celestial world, which demanded the complete sphericity of the stars, were questioned.
The discovery of four Jupiter satellites, for its part, contradicted the principle that the Earth should be the center of all the movements that took place in the sky. As for the fact that Venus had lunar-like phases.
Eager to make his discoveries known, Galileo quickly produced a short text that was published in March 1610 and which soon made him famous throughout Europe: the Sidereus Nuncius, the ‘sidereal messenger’ or ‘messenger of the stars’ , although the title also allows the translation of ‘message’, which is the meaning that Galileo, years later, said he had in mind when he was criticized for the arrogance of claiming the status of heavenly ambassador.
The book was dedicated to the Grand Duke of Tuscany, Cosimo II de ‘Medici, and in his honor Jupiter’s satellites were called’ Medicean planets’ there. With this, Galileo secured his appointment as mathematician and philosopher of the Tuscan court and the possibility of returning to Florence, for which he had been fighting for several years.
The job included an honorary professorship in Pisa, without teaching duties, thus fulfilling a long-held hope and which made him prefer an absolute monarch to a republic like the Venetian, since, as he himself wrote, “it is impossible to obtain any payment of a republic, splendid and generous as it may be, that does not carry any obligation; since, to get something from the public, you have to satisfy the public ».
The battle of Copernicanism
In 1611 a German Jesuit, Christof Scheiner, had observed sunspots by publishing a book about them under a pseudonym. Around the same time, Galileo, who had already observed them previously, made them see various characters during their stay in Rome, on the occasion of a trip that was described as triumphant and that served, among other things, for Federico Cesi to make member of the Accademia dei Lincei that he himself had founded in 1603 and that was the first scientific society of lasting importance.
Under his auspices, the Istoria e dimostrazione internal alle macchie solari was published in 1613, where Galileo was in step with the interpretation of Scheiner, who claimed that the spots were an extrasolar phenomenon (“stars” close to the Sun, which stood between it and the earth). The text sparked a controversy about the priority in the discovery, which lasted for years and made the Jesuit one of the most bitter enemies of Galileo, which was not without consequences in the process that was to follow the Inquisition. Furthermore, it was there that, for the first and only time, Galileo gave the press unequivocal proof of his adherence to Copernican astronomy, which he had already communicated in a letter to Kepler in 1597.
Faced with the attacks of his academic adversaries and the first signs that his opinions could have conflicting consequences with ecclesiastical authority, the position adopted by Galileo was to defend (in a letter addressed to Cristina de Lorena in the middle of 1615) that, even Admitting that there could be no contradiction between Holy Scripture and science, it was necessary to establish absolute independence between the Catholic faith and scientific facts. Now, as Cardinal Bellarmino noted, it could not be said that conclusive scientific evidence was available in favor of the Earth movement, which, on the other hand, was in contradiction with Biblical teachings; consequently, the Copernican system could only be understood as hypothetical. In this sense,
Final part of Galileo’s abjuration document
Galileo, knowing that he did not possess the proof that Bellarmino claimed, even though his astronomical discoveries did not leave him in doubt about the truth of Copernicanism, took refuge for a few years in Florence in the calculation of Tables of the movements of Jupiter’s satellites, with the aim of establishing a new method for calculating lengths on the high seas, a method that he tried in vain to sell to the Spanish and Dutch governments.
In 1618 he was involved in a new controversy with another Jesuit, Orazio Grassi, regarding the nature of comets, which resulted in a text, Il Saggiatore (1623), rich in reflections on the nature of science and the scientific method, which contains his famous idea that “the Book of Nature is written in mathematical language.” The work, edited by the Accademia dei Lincei, was dedicated by the latter to the new Pope Urban VIII, that is, Cardinal Maffeo Barberini, whose election as pontiff filled with joy the educated world in general and, in particular, Galileo, who the cardinal had already shown his affection.
The new situation encouraged Galileo to write the great exposition work on Copernican cosmology that he had already announced in 1610: the Dialogue sopra i due massimi sistemi del mondo, tolemaico e Copernicano; In it, the Aristotelian points of view defended by Simplicio were compared with those of the new astronomy advocated by Salviati, in the form of dialogue moderated by Sagredo’s bona mens.
Although the work failed in its attempt to live up to the demands expressed by Bellarmino, since it provided, as proof of the movement of the Earth, a false explanation of the tides, the inferiority of Simplicio before Salviati was so evident that the Holy Profession did not hesitate to open a process to Galileo, despite the fact that he had obtained an imprimatur to publish the book in 1632. Initiated on April 12, 1633, the process ended with the sentence of life imprisonment, despite Galileo’s resignation to defend himself and his formal retraction.
The sentence was softened by being allowed to serve him in his fifth in Arcetri, near the convent where, in 1616 and with the name of Sister Maria Celeste, his most beloved daughter, Virginia, had entered, who died in 1634.
In his retirement, where moral affliction was added to those of arthritis and blindness, Galileo managed to complete the last and most important of his works: the Discorsi e dimostrazioni matematiche intorno à due nine scienze, published in Leiden by Luis Elzevir in 1638. In it, starting from the discussion on the structure and resistance of materials, Galileo laid the physical and mathematical foundations for an analysis of movement, which allowed him to demonstrate the laws of bass drop in a vacuum and to elaborate a complete theory of projectile firing. The study was supposed to become the foundation of the mechanics science developed by next-generation scientists, with Newton at the helm.
Invention of the telescope
In May 1609, Galileo received from Paris a letter from the French Jacques Badovere, one of his former students, who confirmed an insistent rumor: the existence of a telescope that allows distant objects to be seen. Made in Holland, this telescope would have already allowed you to see invisible stars with the naked eye.
With this unique description, Galileo, who no longer teaches Cosme II de Medici, builds his first telescope. Unlike the Dutch telescope, it does not deform objects and increases them 6 times, that is twice that of its opponent. It is also the only one of the time that manages to obtain a right image thanks to the use of a diverging lens in the eyepiece. This invention marks a turn in the life of Galileo.
On August 21, as soon as his second telescope was finished (it increased eight or nine times), he presented it to the Venice Senate. The demonstration takes place at the top of the Campanile in San Marco square. Spectators are enthusiastic: before his eyes, Murano, located 2 km and a half, seems to be only 300 m away.
Galileo offers his instrument and bequeaths the rights to the Republic of Venice, very interested in the military applications of the object. In reward, he is confirmed for life in his Padua post and his emoluments are doubled. It finally frees itself from financial difficulties.
However, contrary to his claims, he did not dominate optical theory and the instruments he manufactured are of highly variable quality. Some telescopes are practically unusable (at least in astronomical observation). In April 1610, in Bologna, for example, the demonstration of the telescope is disastrous, as Martin Horky reports in a letter to Kepler.
Galileo recognized in March 1610 that, among more than 60 telescopes he had built, only a few were adequate. Numerous testimonies, including Kepler’s, confirm the mediocrity of the first instruments.
The observation of the Moon
During the fall, Galileo continued to develop his telescope. In November, he makes an instrument that increases twenty times. Take the time to turn your telescope to the sky. Quickly, observing the phases of the Moon, he discovers that this star is not perfect as Aristotelian theory wanted it. Aristotelian physics, which had authority at that time, distinguished two worlds:
- the “sublunar” world, which comprises the Earth and everything between the Earth and the Moon; in this world everything is imperfect and changing;
- the “supralunar” world, which begins on the Moon and extends beyond. In this zone, there are only perfect geometric shapes (spheres) and immutable regular movements (circular).
Galileo, for his part, observed a transitory zone between shadow and light, the terminator, which was not at all regular, which therefore invalidated the Aristotelian theory and affirms the existence of mountains on the Moon. Galileo even estimates its height at 7000 meters, more than the highest known mountain at the time. It must be said that the technical means of the time did not allow knowing the altitude of the land mountains without fantasies. When Galileo publishes his Sidereus Nuncius he thinks that the lunar mountains are higher than those of Earth, although in reality they are equivalent.
The head thinking of the stars
In a few weeks, you will discover the nature of the Milky Way, count the stars of the Orion constellation and find that certain stars visible to the naked eye are, in fact, star clusters. Galileo observes Saturn’s rings but does not discover their nature. Also study sunspots.
On January 7, 1610, Galileo makes a capital discovery: he highlights 3 small stars on the periphery of Jupiter.  After several nights of observation, he discovers that there are four of them and that they revolve around the planet. These are the satellites of Jupiter, which he calls Callistus, Europe, Ganymede, and Io, (today called Galilean satellites). On March 4, 1610, he published his discoveries in Florence in The Messenger of the Stars (Sidereus Nuncius), the result of his first stellar observations.
For him, Jupiter and its satellites are a model of the Solar System. Thanks to them, he thinks he can demonstrate that Aristotle’s crystal orbits do not exist and that all heavenly bodies do not revolve around Earth. It is a very hard blow to the Aristotelians. He also corrects certain Copernicans who claim that all heavenly bodies revolve around the Sun.
In order to protect himself from the necessity and doubtless eager to return to Florence, Galileo will for some time call Jupiter’s satellites the “medicinal stars” honor of Cosme II de ‘Medici, his former student and Grand Duke of Tuscany. Galileo did not hesitate between Cosmica sidera and Medicea sidera. The play on words “Cosmica = Cosme” is obviously voluntary and it is only after the first impression that the second name is retained.
On April 10, show these stars to the court of Tuscany. It is a triumph. The same month, he gives three courses on the subject in Padua. Always in April, Johannes Kepler offers his support to Galileo. The German astronomer will not truly confirm this discovery – but with enthusiasm – until September, thanks to a lens offered by Galileo in person.