Galileo Galilei – Founder Father of Natural Science

The name of the outstanding Italian scientist Galileo Galilei is well known even to those who have had no clue about physics, mathematics, and astronomy. His fundamental works and inventions considerably influenced the development of science in the 16th-17th centuries and later periods.


Galileo Galilei was a rationalist who believed that all phenomena and laws of nature had their explanations and were subject to human reason. He had a vivid, interesting, and in many ways difficult life, leaving a significant input in the world history.

Family and background

Galileo Galilei was born in Pisa in 1564 in the family of a nobleman, musician, and composer Vincenzo Galilei. He was an extremely enlightened and educated man.  Unfortunately, he had to deal with petty trade because of his hard financial situation.

Galileo’s mother, Giulia Ammannati, was also of noble birth. She had a problematic and capricious character and devoted her life to raising her children and managing the household. It is known that among the descendants of this aristocratic family (on his father’s side), there were scientists and doctors, some of whom were mentioned in documents dating back to the 14th century. Besides, Galileo’s relatives occupied important posts in the Republic of Florence (Repubblica Fiorentina).

Galileo was the eldest of six children (two died in infancy). When he was about 11 years old, in search of a better life, the family moved to Florence, the center of European culture, science, and art.

See also: How to get from Pisa to Florence.

Early Education

Galileo was a talented child in music and art. As a result, he succeeded in this area significantly.

He received his primary education at the school of the Abbazia di Vallombrosa, located in the small municipality of Reggello in the province of Florence. Galileo was a diligent pupil, studying theology, ancient languages, poetry, and rhetoric. He liked his life in a monastery, and he dreamed of becoming a priest.

Student years

Galileo’s father rejected his idea of devoting himself to the service of God. In 1581 Galileo entered the University of Pisa (Universita di Pisa) in the medical faculty on the insistence of his father, who was seeking a more lucrative occupation for their offspring.

As a secondary course the young student studied mathematics, geometry, physics, and astronomy. Galileo was fully immersed in theory and constantly was putting into scientific experiments. Very quickly, he changed the faculty to the mathematics one. Being a student, Galileo admired heliocentric Copernican theory.

At university, he was not only a knowledge-seeking young man but also a passionate debater. He knew nothing of diplomacy and always had his own opinion, which he did not find it necessary to hide it. Because of his family’s financial difficulties, he could not complete his studies, finishing only three courses. The boy’s intemperance and willful temper (which he had most likely inherited from his mother) played a dirty trick on him. Despite this talent, the faculty refused to let him continue his studies for free. Failing to obtain a professor’s degree, Galileo returned to Florence.

The patronage of Guidobaldo del Monte

Fortunately, the young man’s talent for technical sciences and outstanding abilities were noticed by Guidobaldo del Monte. A famous mathematician, mechanical theorist, astronomer, and philosopher.

Guidobaldo was an extremely rich man and had a position in society, who played an extremely important role in Galileo’s fate. Guidobaldo del Monte became the patron of the young scholar, and he made every effort to present the young talent to the Grand Duke of Tuscany, Ferdinando I de’ Medici, and obtained for him a paid position as professor of mathematics.

So, already in 1589, at the age of 25, Galileo returned to the walls of his alma mater and began teaching. At the University of Pisa, he lectured on mechanics and mathematics, conducted experiments, led researches, and wrote treatises. Unfortunately, Galileo’s enthusiasm for the technical sciences did not bring him much money because the salary he received differed from that of a professor of medicine.

It is noteworthy that Galileo was always experiencing material difficulties throughout his life. In 1591 his father died, and Galileo had to support his mother and two sisters.

Work at the University of Padua

Galileo, who had already had a certain authority in scientific circles and was known as an outstanding theorist and inventor, moved to Padua (Padova) – the great city of the Serenissima Repubblica di Venezia, in 1592. There he has been teaching mathematics, mechanics, and astronomy for 8 years. Galileo held a chair at the University of Padua (Universita degli Studi di Padova), considered the oldest and best educational center in Europe, and this was his most fruitful period as a scholar.

The professor was enormously popular with students eager to attend his class, and the Venetian government constantly commissioned him to design new technical devices. Many of Galileo’s works were translated into other languages. During this period, he achieved universal European recognition and great fame, becoming a legend.

The private life of the scientist

Galileo’s main and only true passion was science. However, it is believed that Galileo had relations with a woman who gave birth to their two daughters and a son. The Venetian-born Marina di Andrea Gamba was of poorer family and lower social status. That is why they were never legally married, even though they had three common children. It is also known that the couple lived together while Galileo was working in Padua.

Leaving the city, the professor took his daughters and his son. Officially the scholar recognized only a son (he confirmed paternity in 1619). The daughters spent their lives in the convent of the church of St. Matthew in Arcetri (Chiesa di San Matteo in Arcetri), a small village near Florence. Being bastards, they had no chance of a happy marriage in those days. Despite this fact, Galileo was in good relations with his children throughout his life.

Life and work in Florence, relations with the Catholic Church

Fame did not relieve Galileo of his incessant need for money. In 1610, hoping to improve his financial situation, the scholar gladly accepted an invitation to move to Florence, where he lived until 1632. A high-paying job as an adviser and teacher at the court of the Duke of Tuscany, Cosimo II de’ Medici, promised him relief from his rising debts. However, he formally retained his position as a professor at the University of Pisa, which did not require lecturing.

As “the first mathematician and philosopher” at the ducal court, Galileo was working on his astronomical research. He stood for the world’s heliocentric system and gathered scientific proof. This caused irritation and dissatisfaction among many church members and followers of the teachings of Aristotle and Ptolemy. By this period, Galileo, eager to fathom the mysteries of the celestial bodies, had already succeeded in making several revolutionary discoveries, which included:

  1. The presence of sunspots;
  2. The rotation of the Sun around its axis;
  3. The rotation of the Earth not only around its own axis but also around the Sun;
  4. The presence of irregularities (mountains and craters) on the surface of the Moon;
  5. Discovery of Jupiter’s satellites;
  6. Discovery of Saturn’s rings;
  7. Observation of the phases of Venus;
  8. Explaining the nature of the Milky Way, consisting of countless stars.

In 1611 the scientist came to Rome to the reception of Pope Paul V in order to prove to the head of the Catholic Church the necessity to keep pace with scientific thought. He demonstrated the telescope he had made, explained his discoveries, and was generally received with warmth and favor. Remarkably, despite later conflicts with the church, Galileo always considered himself a ‘good Catholic’.

Accusations of heresy

Starting from 1611, a series of events significantly influenced Galileo’s future. First, encouraged by the goodwill of the higher clergy, he wrote (and later recklessly published) a letter to his disciple and friend Benedetto Castelli. In this letter, he openly declared that Sacred Scripture was good for faith and penance only and could not serve science as an authoritative source of knowledge about objects and natural phenomena.

Then, in 1613, Galileo’s book ‘On the Sun Spots’ was published. Here he acknowledged the correctness of Copernican theories. As a result, after two years, the inquisitors opened the first case against the scientist. Galileo’s trial was held in Rome in 1616, in parallel the church officially recognized heliocentrism as a dangerous heresy. And although the scientist was acquitted, the verdict obliged him to refuse open support for the Copernican world model and archaic authorities.

In 1633 a second trial was held against the scholar. The reason for the Inquisition’s repeated persecution was the publication of Galileo’s next treatise – ‘Dialogue on the Two World Systems,’ written in Italian so that a wider audience could read it.

It is an important fundamental work that laid the foundations for new mechanics and physics. After working on it for several years, the book was published in 1632 and, after a very short period, was withdrawn from sale.

After his first interrogation, Galileo spent 18 days in prison. They blamed him for heresy and sentenced him to life imprisonment (later changed to house arrest), the inquisitors also required Galileo to renounce all his beliefs (which he did) and forbade him to publish any theoretical or research papers. Many biographers tend to speculate that the scientist was even tortured.

The legendary phrase, “Eppur si muove” (“And yet it turns”), attributed to the scholar, was never his and is nothing more than fiction.

Last years of his life, death, and posthumous rehabilitation of Galileo Galilei

The scientist was seriously ill in his old age, and in 1637 Galileo lost his sight. He could not publish his works, but he did not stop doing science even in spite of his worsening state of health. The inquisitors constantly followed the prisoner to the end of his days, making it difficult for him to communicate with friends and students.

He spent the rest of his life in a small villa in Arcetri, a suburb of Florence, not far from the convent where his daughters were serving. The building has survived to this day and is now the Galileo House Museum (Villa Il Gioiello), owned since 1942 by the Faculty of Astronomy of the University of Florence (Universita degli Studi di Firenze, UNIFI).

In 1642, the great scientist died at the age of 78, surrounded by his followers and son. The Church forbade the burial of the heretic in the family crypt and the erection of monuments to him. The last representative of the famous family, Galileo’s grandson, took the monastic vows and burned his grandfather’s valuable manuscripts. In 1737 the remains of the scholar were reburied in the Basilica di Santa Croce in Florence.

Tomb of Galileo Galilei in the Basilica di Santa Croce in Florence

The tomb is decorated with a marble figure of Galileo and late Baroque allegorical statues representing Geometry and Astronomy. The Italian sculptor Giovanni Battista Foggini was responsible for decorating the sarcophagus.

Only in the second half of the XX century the Catholic Church dropped charges against Galileo. And in 1992, after a special commission, Pope John Paul II officially admitted the error of the Inquisition.

Discoveries of Galileo Galilei

Galileo is rightly considered the founder of natural science. His mind allowed him to discover and formulate the laws of nature on which physics as a science in general and mechanics in particular, as they are understood today, are based. Galileo introduced new methods of investigation based on ephemeral reasoning and references to authoritative dogmas, as well as on observation, experimentation, and mathematical analysis. Discoveries that dramatically changed the scientific worldview include:

  1. The law of isochronally (the period of oscillation of a pendulum);
  2. The law of free fall of bodies;
  3. The principle of motion of bodies on an inclined plane;
  4. The law of addition of motions;
  5. The principle of relativity;
  6. The law of inertia.

The scientist also made a significant contribution to the development of the mathematical theory of probability and sets. He investigated the nature of light, measured the density of air, and dealt with issues of physical optics. Galileo’s major inventions, which influenced many areas of human life, included:

  1. Hydrostatic scales for determining the density of bodies;
  2. The thermoscope, an analogue of the modern thermometer;
  3. The telescope and the inverse of the device, the microscope;
  4. The proportional compass to change scale.

Galileo was an inventor from his early years until his old age, constantly inventing new instruments and devices.

Creation of the telescope

The telescope is one of Galileo’s greatest and most important inventions. It significantly accelerated understanding of the solar system.

The first copy was presented to the public in 1609. Galileo worked on the basis of “telescope” invented by Johann (Hans) Lippersgeij, a spectacle-maker from Middelburg (Netherlands), and improved it.

Galileo perfected the Dutch optical device and gave it its current name.  Ancient Greek word ‘telescope’ literally translates as “to look far.” The Italian professor succeeded, unlike his predecessor, in magnifying the image thirty times.

Thanks to the telescope, he made detailed sketches of the lunar surface, discovered sunspots, studied the nature of the Milky Way, assumed the existence of other galaxies. Besides, Galileo made a number of other revolutionary discoveries describing them in his treatise published in 1610 “The Starry Messenger. The book became a real sensation in Europe, and its fame even reached China.

It is noteworthy that Galileo created about a hundred telescopes during his lifetime, he gave copies of the invention to members of the higher clergy and monarchs and even tried to establish industrial production but did not want to share the secret of the lens with fellow astronomers.

Interesting Facts

  1. Although Galileo was the first to formulate the laws of universal acceleration, there is no evidence that he ever dropped balls from the Tower of Pisa to prove them.
  2. When Galileo thought he had discovered several Saturns, he concealed his findings by encoding them in an anagram.
  3. He sketched out ideas for his future inventions.  This includes a combination of candles and mirrors to reflect light through a building, an automatic tomato picker, a pocket comb that doubled as flatware, and a ballpoint pen.
  4. After his father died and, fearing debtor’s prison, he made his living by designing a military compass for aiming cannonballs. His earlier invention, the first thermometer to measure temperature fluctuations, failed.
  5. For a brief period, he worked as a drawing teacher in Florence.
  6. In 1610, Galileo was the first astronomer to discover the four moons of Jupiter. These cosmic bodies were named “Galileo’s moons” in his honor. The four moons associated with Galileo are Io, Europa, Ganymede, and Callisto. The largest of Galileo’s moons is Ganymede. Thus he discovered the first satellites ever known to orbit a planet other than Earth.
  7. After 400 years, Galileo’s telescope is still alive, and you can see it at the Istituto e Museo di Storia della Scienza in Florence. In the museum, you will find Galileo’s two telescopes and lenses. Address of the museum: Piazza dei Giudici, 1, 50122 Firenze. Official website:
  8. He could not publish his book while under house arrest. However, it was published in Holland in 1638.
  9. They say that Galileo went blind because he observed the sun for a long time while looking at sunspots with his telescope.
  10. Galileo was depicted on the Italian banknote of 2,000 lire.Galileo Galilei on the Italian 2000 lire bank-notes
  11. Pisa International Airport (Aeroporto Internazionale di Pisa, di Aeroporto Galileo Galilei, IATA code: PSA) is named after the Italian scientist.
  12. He established that in the absence of air resistance, gravity accelerates all objects equally, regardless of their mass.
  13. Galileo was against Kepler’s theory that the moon was causing the tides on Earth and instead believed it was due to the rotation of the Earth. Surprisingly, Kepler supported Galileo for his work, publishing letters of support at the time.
  14. Initially, Galileo’s telescope could only magnify an image eight times. However, he soon improved it to provide twenty times magnification.
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