GALILEO GALILEI

Galileo Galilei was born in Pisa  on February 15, 1564. His parents were Vincenzo Galilei from Florence and Giulia degli Ammannati. In 1574 his family left Pisa and moves to Florence. In 1581 Galileo goes to the University of Pisa in order to study Medicine, following his father's will. I During the studies he gets interested in Physics  and in 1583 he states the theory of the isochronism of the pendulum, which he guessed by observing the oscillations of a lamp inside the Pisa Cathedral.

In 1585 he goes back to Florence quitting University, and begins his activity in Physics and Mathematics, also giving private lessons. In 1586 he invents the hydrostatic balance.
In 1588 he obtains a chair at the Pisa University, which he holds until 1592. During this time he gets interested to the motion of the falling bodies and writes "De Motu".
In 1591 his father Vincenzo dies, leaving him as the guide of the family.
 

In 1592 Galileo obtains a chair of Mathematics (Geometry and Astronomy) at the Padova University, where he will stay until 1610. During this time he turns to the  Copernican theory of the planetary motion.
In 1599 he meets Marina Gamba, who will give him three children:  Maria Celeste, Arcangela and Vincenzo.

In 1602 he carries out a few experiments on the pendulum, during a study of the accelerated motion. In 1606 he invents the  thermoscope, a primitive thermometer.
In the following years he devotes himself to studies about hydrostatics and about the resistance of materials, he builds his  hydrostatic balance and discovers the parabolic motion of projectiles.
In 1604 Galileo observes a supernova, which appeared in the sky during the fall of the year.
 

In 1609, while Kepler publishes his "New Astronomy", which contains his first two laws of the planetary motion, Galileo gets interested to a new instrument, built in Holland: the telescope.  Until that moment, the astronomical observations were made by naked eye.
After improving it  in some ways, he presents a sample to Venice's Senate, which he calls "perspicillum".
With his new instrument, in Padova Galileo carries out a series of observations of the  Moon in December, 1609, and on January 7, 1610 he observes a few luminous "small stars" near Jupiter. In March, 1610, he reveals in  "Sidereus Nuncius"  (The Starry Messenger) that they are 4 satellites of Jupiter, which he later names "Astri Medicei" to honour  Cosimo II de' Medici, Grand Duke of Tuscany. It is only in later times that the satellites, due to a suggestion by Kepler, the satellites will be named as we know them today: Europa, Io, Ganymede and Callisto.
The discovery of a centre of motion which is not the Earth starts begins sapping the foundations of the  Ptolemaic theory of the Cosmos.

In July, same year, Galileo observes Saturn with his telescope: since he cannot distinguish its rings with his instrument, he believes that it is composed by three separated celestial bodies, and he names it three-bodied Saturn.
 

While other astronomers all over Europe (among whom Kepler) are observing the jovian satellites, Galileo (who in the meantime went back to Florence)  observes the  Venus phases and the Sun spots.
In 1611 the scientist is admitted to the "Accademia dei Lincei".
 

In the following years a debate is started about his discoveries; the interpretation given by the scientist refuses the Ptolemaic theory of the motion, which in those years was officially adopted by the scientific and religious world, and instead supports the Copernican theory.
The Inquisition brands this theory as an heretic one, and formally forbids Galileo to support it.
The book "De Revolutionibus Orbium Coelestium"  by Copernicus is set on the Index.
In April, 1630, Galileo completes his  "Dialogo sui due massimi sistemi del mondo", (Dialogue concerning the two chief world systems) where the Copernican and Ptolemaic theories are compared; later he agrees with the Vatican on some changes in order to print the book, but he then decides to have it printed in Florence, in 1632.
The Pope Urban VIII, after examining the "Dialogue", forbids its distribution and asks the Inquisition to set up a trial against Galileo.
 

The scientist, now old and ill, is called to Rome in 1633, where he is tried and requested to abandon the Copernican theory. Imprisoned and threatened with torture, he is forced to publicly abjure, and he is sentenced to life prison, but later he is allowed to serve the sentence in his Arcetri villa, near Florence.
 
 

In July, the same year, he begins writing the "Discorso intorno a due nuove scienze attinenti alla meccanica e ai movimenti locali"
(Discourse concerning two new sciences of mechanics and local motions). He dies, ill and blind, on January 8, 1642, in the Arcetri home.