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Early life -

Galileo Galilei was born in Pisa, Italy, on February 15, 1564. In 1581 he entered the University of Pisa and began studying medicine.

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Early life -

However, over the course of his studies, he found himself drawn more towards Euclidean geometry, mathematics, and scientific research. Four years in, he abandoned medicine.

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Experimentation -

When Galileo left the university without a degree in 1585, he began experimenting with pendulums and hydrostatic forces. He also gave private lessons in mathematical subjects.

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Dante's Inferno lectures -

In 1588, Galileo had his first university appointment, teaching art at the Accademia delle Arti del Disegno in Florence. During this time, he gave two published lectures on the dimensions of Dante’s Inferno to the Academy.

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Gaining attention -

He continued publishing theorems on topics such as the centers of gravity, which gained him the attention of his contemporaries. He received the patronage of a nobleman and the author of several works about mechanics, Guidobaldo del Monte. 

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University of Pisa appointment -

Thanks to his patronage and growing reputation, the following year at the age of just 25, Galileo was appointed to the role of Chair of Mathematics at the University of Pisa.

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Tower of Pisa experiment -

While teaching at the University of Pisa, Galileo dropped bodies of different weights from the top of the famous Leaning Tower. In doing so, he demonstrated that the speed of the fall of a heavy object is not proportional to its weight, which had been claimed by Aristotle.

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Rejection of Aristotle -

Instead, Galileo’s observations directly contradicted the Aristotelian view of the universe. Initially, this made Galileo unpopular, as Aristotle's views were widely accepted by both scientists and theologians. His contract at the University of Pisa was not renewed as a result.

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University of Padua (1592-1610) -

Luckily, his patrons were able to secure him a role teaching at the University of Padua, where he was tenured between 1592 and 1610.

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First telescope -

In 1609, Galileo designed his first telescope. He managed to design and make it using only limited descriptions of the earliest telescopes, which had been created a year earlier in the Netherlands. 

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Presentation to lawmakers -

He presented one of his first telescopes to lawmakers of the Venetian Senate in August 1609, which had eight to nine times magnification. It enabled magnified images of Earth but it could also be used to observe the sky.

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Continued improvements -

Galileo kept improving upon his design, reaching a magnification of up to 30 times. He was able to draw the Moon's phases and discovered its surface was uneven. In 1610, he discovered four moons around Jupiter.

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Sidereus Nuncius: Starry Messenger -

He then produced his findings in Sidereus Nuncius, or 'Starry Messenger,' his first book on astronomy. Published in 1610, it put forward the idea that the Earth was not the center of our Universe.

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The de Medici family -

Galileo had tutored Cosimo II de Medici (1590–1621), the grand duke of his native Tuscany, for several summers. He dedicated 'Starry Messenger' to him, and named the moons of Jupiter after the de Medici family: the Sidera Medicea, or "Medicean Stars."

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Celebrity -

As a result of 'Starry Messenger,' Galileo became a celebrity in Italy. He began to live the life of a gentleman and continued to sell telescopes to merchants as a sideline income.

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Friends and enemies -

Galileo certainly had a flair for self-promotion. It would earn him powerful friends among Italy’s ruling elite, such as the de Medici's. However, it also created enemies among the Catholic Church’s leaders. He was first summoned by the Roman Inquisition in 1615, to defend the ideas put forward in 'Starry Messenger.'

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Venus and Saturn discoveries -

Before leaving Padua, Galileo discovered the strange appearance of Saturn, which would later be revealed to have rings around it.

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Venus and Saturn discoveries -

What he uncovered about the phases of Venus and Mercury demonstrated that they revolved around the Sun, not the Earth. These observations appeared to help confirm the central tenet of heliocentrism.

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Nicolaus Copernicus -

The first modern scientific argument for a heliocentric (sun-centered) universe was put forward in Nicholas Copernicus’s "De Revolutionibus," in 1616. It was promptly banned by the Catholic Church.

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Sunspots -

Galileo was an independent discoverer of sunspots. In 1613 he published Istoria e dimostrazioni intorno alle macchie solari e loro accidenti —"History and Demonstrations Concerning Sunspots and Their Properties," or "Letters on Sunspots."

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Il Saggiatore (The Assayer) -

In 1623, Galileo published Il Saggiatore — The Assayer. This work was a polemic on physical reality and detailed the Scientific Method, making it one of the first to do so.

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The new Pope's blessing -

A friend, admirer, and patron of Galileo (Maffeo Cardinal Barberini) became Pope Urban VIII around the time of publication. Galileo went to Rome to present his theory about the tides. He was given permission to write about universal theories, with the caveat that Copernican theory could only be treated as hypothetical.

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Dialogue Concerning the Two World System -

In 1630 Galileo published his most famous work, Dialogo sopra i due massimi sistemi del mondo, or 'Dialogue Concerning the Two World System.'

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Dialogue Concerning the Two World System -

In it, Galileo supposedly puts forth hypothetical arguments for both sides of the heliocentrism debate. However, his attempt at balance was unsuccessful. 

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Heliocentrism -

Notably, the person in the text advocating for geocentrism, or that the Universe revolves around the Earth, was called "Simplicius."

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Heliocentrism -

The main reason why the Church was so opposed to the concept of heliocentrism was that passages of the Bible referred to the fixed nature of the Earth. On publishing 'Dialogue...,' he had alienated his most powerful supporter—the Pope.

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The Roman Inquisition, 1633 -

In 1633, three years after the publication of 'Dialogue...,' he was called before the Roman Inquisition for a second time. 

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The Roman Inquisition, 1633 -

He denied advocating for heliocentrism at first, but later backtracked and said he'd done so unintentionally. He was found guilty of a charge almost equivalent to heresy.

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House arrest and continued work -

Galileo was sentenced to imprisonment but this was commuted to house arrest, which he remained under for the rest of his life.

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House arrest and continued work -

However, Galileo continued working and writing, and in 1638 released Discorsi e dimostrazioni matematiche intorno a due nuove scienze attenenti alla meccanica (Dialogues Concerning Two New Sciences). It was published in Holland to avoid censorship, and summarized his findings on motion. The work was later praised by Albert Einstein. Galileo passed away in 1642.

Sources: (Britannica) (History Channel) (Online Education)

See also: The greatest discoveries and advancements in the history of astronomy

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