Born in Pisa on 15 February 1564, Galileo completes his first studies in literature and logic in Florence where he moved with his family in 1574. In 1581, at the behest of his father, he enrolled at the Faculty of Medicine of the University of Pisa, but for this discipline it will not show a real interest. So left the Pisan university returns to Florence. Here he develops a passion for mechanics by starting to build increasingly sophisticated machines, deepening mathematics and making observations of physics with the guidance of Ostilio Ricci.
As time passes, he formulates some theorems of geometry and mechanics. From the study of Archimedes in 1586 he discovered the "balance" to determine the specific weight of the bodies (the famous hydrostatic balance).
In 1589 he obtained the chair of mathematics at the University of Pisa, which he held until 1592; in 1591 his father Vincenzo died leaving him at the helm of the family; in this period he is interested in the movement of falling bodies and writes the "De Motu".
In 1593 Galileo was called to Padua where the local University offered him a prestigious chair in mathematics, geometry and astronomy. Galileo agrees with enthusiasm and will remain there until 1610.
It is in this period that he begins to move towards the Copernican theory of planetary motion, supported by the observations made with a new instrument built in Holland: the telescope, Galileo will then bring significant improvements to the instrument. In 1609 he published his "New astronomy", which contains the first two laws of planetary motion.
In Padua with the new instrument Galileo makes a series of observations of the moon in December 1609; is January 7, 1610 when he observes the "bright little stars" near Jupiter. In March 1610 he reveals in the "Sidereus Nuncius" that it is four satellites of Jupiter that will baptize "Astri Medicei" in honor of Cosimo II de 'Medici, Grand Duke of Tuscany.
Only later, at the suggestion of Kepler, will the satellites take the names with which they are known today: Europa, Io, Ganymede and Callisto.
The discovery of a center of motion that was not the earth begins to undermine the Ptolemaic theory of the cosmos. The astronomical theories of Galileo Galilei are soon considered incompatible with the truths revealed by the Bible and the Aristotelian tradition.
A first consequence is a formal admonition by Cardinal Bellarmino. Galileo after all does nothing but confirm the Copernican theory theory already known for some time.
The ecclesiastical Inquisition does not hear reasons, as a heretical bubble this cosmological plant and formally forbids Galileo from supporting such theories. As if this were not enough, the text "De Revolutionibus Orbium Coelestium" of Copernicus is put to the index.
In April 1630 Galileo, intimidated but not sufficiently to interrupt his extraordinary scientific exploration, ended writing the "Dialogue on the Two Worlds Systems of the World", in which Copernican and Ptolemaic theories are dialectically compared, and then naturally demonstrate the superiority of new scientific acquisitions.
He also agrees with the Church to make some changes to print the work, but then decides to have it printed in Florence, in 1632. Having arrived in the hands of Pope Urban VIII, he prohibits its distribution and has instituted a trial against Galileo by the Inquisition. .
The scientist, now elderly and ill, is called to Rome and tried (1633). Imprisoned and threatened with torture, Galileo is forced to publicly abjure (humiliated he wore a rough sack) and sentenced to life imprisonment. It is said that on the occasion Galileo was murmuring between his teeth "Eppur moves".
The sentence was then commuted to what we would now call "house arrest": he is allowed to serve his sentence in his villa in Arcetri, near Florence, prison and exile until his death.
This colossal scientist and thinker to whom we owe the fundamental building blocks of scientific progress as we know it today, died in Florence on January 8, 1642, surrounded by a few students and almost total blindness.
Galileo owes the law of the pendulum (the time of the oscillations is constantly the same, whatever their amplitude): those who go to the Cathedral of Pisa can still admire, suspended at the very high ceiling of the temple, the lamp that with its oscillations inspired the young Galileo precisely the invention of the pendulum as a regulator of a mechanical movement.
Galileo Galilei is buried in Florence, in Santa Croce, in the mausoleum of Italian summits.
Three hundred and fifty years after his death (1992), the Church formally recognized the greatness of Galileo Galilei, "rehabilitating" him and acquitting him of the accusation of heresy.