Galileo Galilei (1564-1642) was a physicist, mathematician, and astronomer from the Renaissance who studied mechanics, celestial bodies, and their trajectory. The moons of Jupiter and the solar phases of Venus are among his most important discoveries, which is why he is known as the father of modern astronomy. Are you interested in learning more about his life and work? There is more information about Galileo Galilei in this short biography.

Summary of Galileo Galilei’s life

The index

  • Children are born with an innate talent for mathematics

  • Discovering what you are passionate about as a young person

  • The inventions and philosophy of Galileo Galilei in his early years

  • Aristotle vs Galileo Galilei: the free fall

  • First book on the movement, De Motu Antiquiora

  • The Greatest Discovery of Sidereus Nuncius

  • Sidereus Nuncius: Reactions

  • Catholic censorship

  • The new pope and Galileo Galilei

  • Galileo Galilei’s death and the birth of two new sciences

  • Galileo Galilei’s works

Mathematics innate talent from childhood

Galileo Galilei Ammannati is his full name. When Pisa was part of the Duchy of Florence, he was born on February 15, 1564. The first of his six children was born on that day to Vincenzo and Giulia Galilei. He was baptized in honor of an important ancestor of the family: Dr. Galileo Bonaiuti. He was also hoped to become a renowned doctor by his father. A good future could be secured by restoring the family name.

Galilei was both a music theorist and a good composer. Additionally, he had mathematical skills, which enabled him to establish the relationship between the tension of the string and the tone it produced. Although he had many talents, he had to temporarily work in the cloth trade in order to support his family.

At the age of 10, Galileo’s family moved to Florence, and he spent the next two years studying in a Christian convent. During this time, he began to show an interest in ecclesiastical life, which his father did not appreciate. When Vincenzo learned of Galileo’s growing inclination, he immediately removed him from the institute.

Discovering what you are passionate about as a young person

Galileo Galilei studied medicine in Pisa, where some of the best doctors in Italy worked in the early 1580s. Interestingly, it was here that he discovered his true passion was mathematics, which he inherited from his father.


The life of Galileo Galilei is notable for the fact that, while studying medicine, he was distracted by observing the movement of a chandelier that oscillated due to the force of the wind. Every time it turned, it drew a larger curve, but Galileo believed that the oscillation time remained constant. As soon as he got home, he applied different forces to two pendulums. In this way, he discovered oscillating bodies are isochronous.

When Galileo Galilei walked into a geometry class by mistake, he discovered that mathematics fascinated him more than anything else in the world. Over the years, he has tried to convince his stern father to let him change careers. Galileo was finally able to study mathematics and natural philosophy after much insistence.

The inventions and philosophy of Galileo Galilei in his early years

He devoured every book on the subject in 1583, when he started his first scientific investigations. He was most inspired by Euclid, Archimedes, Pythagoras, and Copernicus. From the beginning, he disagreed with Aristotle’s ideas that the functioning of nature could be understood by logical analysis alone (without the need for experiments).

In addition to teaching private classes, the young scientist studied applied mathematics, mechanics, hydraulics, and later, astronomy. In addition, he created the first thermometer, called the thermoscope. After he turned 22, he designed the hydrostatic balance. In the latter case, water weight was used to determine the volume of objects.

Make something possible if you find something you can’t measure. Galileo Galilei.

Aristotle vs Galileo Galilei: the free fall

Galileo’s most outstanding experiment was based on the principle of the pendulum movement: the free fall of bodies. To determine the fall rate of two spheres of different weights, he placed them on an inclined surface, which is commonly believed to have been on the Tower of Pisa.

It contrasted with the Aristotelian principle that heavier bodies must fall before lighter ones, which seemed so logical to the common academic that he did not dare to contradict it. Galileo had disproved Aristotle by discovering that regardless of weight-and negating air resistance-all objects fall at the same speed. In addition, he discovered acceleration as well!

Please note

The Principia Mathematica and the universal law of gravity were based on Galileo’s experiments decades later by Isaac Newton.

His first book on the movement was De Motu Antiquiora

Galileo was appointed chair of mathematics at the University of Pisa in 1589. The harsh death of his father two years later forces him to care for his younger siblings. He then accepted the position of chairman of mathematics at the University of Padua in 1592. A major part of Galileo’s life during this period was writing De Motu Antiquiora (translated as “The oldest writings on motion” in English). This is one of his most important works.

In addition to the results of his previous experiments, this book contains his critique of Aristotle’s views on physics and astronomy. Even though Galileo made multiple versions of De Motu, he never published it or completed a final draft. Its purpose is unknown.

The greatest discovery of Sidereus Nuncius

Galileo Galilei built the first astronomical telescope in mid-1609. Galileo used this instrument to study the movement of the planets and obtain important and irrefutable findings, which he later had to censor. One of them was the discovery of small satellites revolving around Jupiter, which Galileo believed indicated not everything should revolve around the Earth.

For me, the universe is a book… a mathematical book. It consists of geometric figures instead of letters, without which man would not be able to understand how it works. Galileo Galilei.

As well, he observed that Venus had phases similar to those of our moon, which was incompatible with any geocentric model. However, it did fit perfectly into Copernicus’ heliocentric model. His most controversial work was published in March 1610: Sidereus Nuncius (‘The sidereal messenger’), the first astronomical treatise based on telescope observations and the first to support heliocentrism scientifically.


It is widely believed that Galileo Galilei discovered that the Earth was round. There is no evidence that the astronomer made such a claim, despite defending heliocentrism.

Sidereus Nuncius: Reactions

Sidereus Nuncius spread rapidly throughout Italy and England, generating equal parts hostility and adulation. Clearly, Galileo did not anticipate the work attracting attention outside of the scientific community as well; works of art, poems, and texts were inspired by this new way of looking at astronomy. Even the astronomers themselves were fascinated by Jupiter’s moons.

Others argued that Galileo’s telescope was defective and produced points of light that distorted his observations. Astutely, the astronomer named them “Medician stars,” after the Medici family. It was possible to guarantee the support of the State by flattering the nobles in such a way.


Kepler was the first astronomer to publicly defend Galileo Galilei’s discoveries. In fact, he himself succeeded in describing the heliocentric motion of the planets mathematically shortly after Sidereus. There was only one piece missing to complete the puzzle: What kind of force allowed this movement to take place? The world wouldn’t know the answer for almost 8 decades.

Catholic Church censorship

Within a short time of the new scientific tendency gaining followers, the Inquisition started retaliating. Since Galileo Galilei had not considered the impact his scientific predictions would have on faith, he immediately traveled to Rome to request an audit from the authorities.

It was censored because the Catholic Church considered Aristotle’s and Ptolemy’s geocentric theories to be closest to the descriptions of the universe in the Holy Scriptures. Aristotle’s teachings were therefore considered heretical.

He argued that the Bible should not be read as a scientific text because its purpose was not scientific dissemination. Galileo believed that when the scriptures deviated from common sense, they did so in an allegorical sense. Despite Copernicanism’s efforts, the Church rejected it. As a warning, Galileo was prohibited from defending the heliocentric theory in the future.

We are endowed with intelligence and logical sense, yet God does not allow us to use them since he has already provided “all the information we need.” Galileo Galilei.

The new pope and Galileo Galilei

During the pontificate of an old friend of our scientist in 1623, he saw a glimpse of free speech. This is how he obtained permission to write and publish a book on the subject, as long as it was completely impartial and objective. The essay must also conclude by arguing that “God can take paths unimaginable and incomprehensible to human logic”, and that therefore “man cannot determine how the world works”.

So he did. Galileo was as impartial as he could be, and for this he used a very particular style in his next book: Dialogues on the two greatest systems of the world. The work is based on a hypothetical conversation between two interlocutors (Copernican vs Aristotelian). In addition, it emphasizes the participation of a third party, who establishes his logical point of view. In 1632, Dialogues became available in Italian, rather than Latin, as was customary in scientific essays.

Please note

It was Galileo Galilei’s serious mistake to make Simplicio, the defender of Aristotelianism, constantly see himself trapped in his mistakes, which destroyed his credibility. Possibly this was not intended, and any debate could weaken geocentrism by itself. Simplicio, however, was the only one who said the pope’s words, not one of the other -apparently smarter- interlocutors.

A literary and philosophical masterpiece, Dialogues sold throughout Europe. Moreover, he was also converting many people to Copernicanism, to his misfortune. The Inquisition recalled Galileo and sentenced him to life house arrest for “suspicion of heresy”. His last book was also banned, and it did not leave the Index (the Catholic Church’s literary blacklist) for two centuries.

A new science and the death of Galileo Galilei

Galileo Galilei claimed to have not taken sides in the Dialogues before and after his trial. From his first warning, he also claimed to have abandoned Copernican ideas. They tried all kinds of methods to convince Galileo to tell the truth, but they weren’t very successful. Despite being tortured and interrogated, the astronomer never admitted to supporting Copernicanism.

After suffering a sudden fever and strong heart palpitations, Galileo Galilei died at the age of 77 on January 8, 1642. According to popular legend, Galileo whispered “And yet he moves…”. It’s unclear whether it was just before he died or shortly after he denied the Copernican position.

Galileo Galilei was able to lay the foundations of mechanics (static and dynamic) during his years in prison, however. As a result, science separated itself definitively from Aristotelian physics.

Galileo Galilei’s works

  • Galileo did not write an autobiography, but a young assistant accompanied him during his last years. Vincenzo Viviani is known for being the author of Galileo Galilei’s first biography.

  • Three versions of Bertolt Brecht’s play about Galileo Galilei were written in 1939 by the famous playwright.

  • Later, the Galilean satellites were renamed after their discoverer, Galileo.

  • Galileo Galilei Planetarium, located in the capital of Argentina, is the most famous planetarium in the world. Founded on June 13, 1967, it has an observatory and performs didactic shows every year to promote the dissemination of astronomical scientific knowledge.

  • Likewise, Villa Alemana, Chile, named one of its main schools after Galileo.

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