Biography of Galileo Galilei Italian scientist and astronomer, initiators of experimental physics. Galileo has been indelibly associated with the defense of the movement of the Earth and the planets around the Sun.

Family and studies of Galileo

Galileo Galilei was born in Pisa on February 15, 1564.

His father, Vincenzo Galilei, was a Florentine from a family that had long ago been illustrious. Galileo was the first-born of seven brothers.

In 1581, Galileo entered the University of Pisa, where he enrolled as a medical student.

Pisa is a city in the Italian region of Tuscany, known for its iconic Leaning Tower. Credit: web “”

Four years later, he dropped out of college without earning a degree. However, having lost interest in his career as a doctor, apart from his university studies, he had started in mathematics.

Professional life of Galileo Galilei

Galileo is one of the initiators of experimental physics. However, his name has been indelibly associated with the defense of the movement of the Earth and the planets around the Sun.

Between December 1609 and January 1610, with the help of the telescope that he himself built , Galileo made the first observations of the Moon, proving the existence on our satellite of mountains and craters that showed a similarity to Earth.

The Moon and its craters. Credit: web “”

Also with his telescope, around the year 1610, Galileo could observe the phases of Venus.

These facts radically invalidated geocentric cosmology and confirmed the validity of the theory of Copernicus.

Venus phases
Phases of Venus. Credit: web “”

Galileo discovered four moons orbiting Jupiter. He numbered them from 1 to 4 and called them “Medicean planets” in honor of the Grand Duke Cosimo II de Medici.

This finding definitely demolished the theory that the Earth was the center of all the movements that took place in the sky.

Jupiter and some of its moons. Credit: Wikipedia

These momentous discoveries were the ultimate thrust to overturn the cosmological theories of Ptolemy and Aristotle.

Eager to make them known, Galileo hastily drew up a short text that was published in March 1610 and which soon made him famous throughout Europe: the “Messenger of the Stars”, which was dedicated by Cosimo II de Medici.

Triumph of Galileo in Florence

With this, Galileo ensured his appointment as a mathematician and philosopher of the Tuscan court and the possibility of returning to Florence.

The job included an honorary professorship at Pisa, with no teaching obligations.

Florence, capital of the Tuscany region in Italy.   Credit: web “”

In 1611, Christof Scheiner (a German Jesuit), observed the sunspots and published a book (under a pseudonym) in which he affirmed that the sunspots were an extrasolar phenomenon (stars close to the Sun, which stood between it and the Earth).

In 1613, in the book “History and demonstration of the solar machinery“, Galileo who had previously observed these spots and on the occasion of a trip he made to Rome, showed them to the ecclesiastical authorities.

He came to the step of the interpretation of Scheiner, stating that the spots were from the Sun and not an external phenomenon.

The text triggered a controversy that lasted for years and made the Jesuit one of Galileo’s fiercest enemies.

Galileo’s difficulties with ecclesiastical authorities

In 1618, Galileo was involved in a new controversy with another Jesuit, Horacio Grassi, about the nature of comets.

As a result Galileo wrote a text, rich in reflections on the nature of science and the scientific method.

The work was dedicated to the new Pope Urban VIII, and in which Galileo affirmed that “the book of nature is written in mathematical language.”

Cardinal Roberto Belarmino (Jesuit), proclaimed that there was no conclusive scientific proof in favor of the movement of the Earth, which was in contradiction with biblical teachings.

Consequently, on February 23, 1616, the Holy Office condemned the Copernican system as false and opposed to the Holy Scriptures.

Galileo was admonished and given the strict order not to teach the theories of Copernicus publicly.

Galileo took refuge for a few years in Florence, dedicating himself to the making of tables of the movements of the satellites of Jupiter, in order to establish a new method for the calculation of longitudes on the high seas.

He tried in vain to sell this method to the Spanish and Dutch governments.

The new situation encouraged Galileo to write the great work of exposition of Copernican cosmology that he had already announced in 1610.

In it, the Aristotelian views were confronted with those of the new astronomy, in the form of dialogue.

Process and conviction of the Inquisition

The Holy Office did not hesitate to open a process, despite the fact that Galileo had obtained an imprimatur to publish the book.

Begun on April 12, 1633, the process ended with a life sentence, despite Galileo’s refusal to defend himself and his formal retraction.

The penalty was softened by allowing him to serve it in his villa in Arcetri, near Florence and the convent where in 1616 had entered his dearest daughter, Virginia.

Galileo’s house in Arcetri. Credit: wikipedia

In his retirement, where arthritism and blindness added to moral distress, Galileo managed to complete the last and most important of his works: the “Discourses and mathematical demonstrations around two new sciences”, published in Leiden in 1638.

In it, Galileo laid the physical and mathematical foundations for an analysis of motion, which allowed her to demonstrate the laws of falling bodies in a vacuum and to develop a complete theory of projectile firing.

The work was destined to become the cornerstone of the science of mechanics built by the scientists of the next generation, with Newton at the helm.

Last years and death of Galileo

In the last years of his life, Galileo was authorized to settle near the sea, in his house in San Giorgio.

There he remained surrounded by his disciples (Viviani, Torricelli, Peri) and working on astronomy and physics.

Galileo Galilei died on January 8, 1642 and was buried in the Santa Cruz church in Florence.

It is still curious that 300 years later, on January 8, 1942, another giant of science was born in Oxford, the famous Stephen Hawking.