The Life of Galileo

The Father of Astronomy

Galileo Galilei was an Italian physicist, mathematician and astronomer who played a major role in the Scientific Revolution in the 17th Century. 

Galileo’s achievements included improvements in telescope design, and support for the heliocentric theories of Nicolas Copernicus. Galileo is sometimes called the Father of Astronomy and the Father of Science. For these reasons, Galileo is considered to be one of the great minds of the Renaissance.

Galileo’s Childhood

Galileo Galilei was born on February 15, 1564 in Pisa, to Vincenzo Galilei, a noted musician and composer at the time. Galileo was the oldest of six children, four of whom survived to adulthood.

When Galileo was eight years old his family moved to Florence. At the age of ten, Galileo was sent to the Camaldolese Monastery 35 km southeast of Florence to be educated. While he was there, Galileo seriously considered entering the priesthood. However, he enrolled at the University of Pisa, at his father’s urging, where he studied medicine. Galileo did not complete his medical degree, however, and graduated with a degree in mathematics instead. In 1589, Galileo was appointed Chair of Mathematics at the University of Pisa. In 1597, Galileo’s father died and he was entrusted with the care of his younger brother, Michelangelo. A year later, he accepted a position at the University of Padua as a professor of geometry, mechanics and astronomy. He stayed in Padua until 1610.

In 1610, Galileo published an account of his observations of the moons of Jupiter. He used these findings to bolster support for heliocentric astronomy. In 1611, Galileo visited Rome, where he demonstrated his telescope for a number of influential philosophers and scientists at the Jesuit-run Collegio Romano. In 1612, opposition to heliocentrism began to grow more heated. In 1614, Father Tommaso Caccini publicly denounced Galileo and accused him of being close to heresy. In 1616, Galileo returned to Rome to defend himself, but he was personally handed an admonition by Cardinal Roberto Bellarmino, not to advocate or teach the ideas of Nicolas Copernicus. In 1632, Galileo was ordered to appear before the Holy Office in Rome, where he was to be tried by the Inquisition for supporting heliocentric astronomy.

Galileo’s Trial

Galileo defended heliocentrism by claiming that the Earth orbiting the sun was not in violation of Scripture, particularly Palms 93:1 and First Chronicles 16:30. Galileo took the position of St. Augustine, and argued that not every passage in the Bible is meant to be interpreted literally.

By 1616, the attacks on Copernicus had reached a head and Galileo went to Rome to try to persuade the Church not to ban Copernicus’s ideas. However, he was forced to desist from studying heliocentrism for several years by Cardinal Bellarmino.

Galileo was able to revive his project of writing a book on the subject of heliocentrism, thanks to the election of Cardinal Barberini to the Papacy as Pope Urban VIII, in 1632. Pope Urban asked Galileo to write a book outlining the arguments both for and against heliocentrism. Pope Urban also asked that his own views be included in Galileo’s book. In spite of these requests and Galileo’s own good intentions, his book, Dialogue Concerning the Two Chief World Systems, caused a firestorm of controversy when it was published. The reason for this is because of a character in the book named Simplico. Even though Galileo stated in the book’s preface that Simplico was named after a famous Aristotelian philosopher named Simplicus, in Italian Simplico can also be interpreted as simpleton. Galileo’s error was compounded by the fact that Galileo put the words of the Pope in the mouth of Simplico. Galileo was found guilty of heresy and sentenced to house arrest.

Galileo’s Legacy

In spite of being persecuted by the Church, Galileo made many contributions to math and physics, in addition to being a pioneer in the field of astronomy.

Based on only vague descriptions of the first telescope, which was developed in the Netherlands in 1608, Galileo built his own telescope in 1609, with a 3x power magnification. He eventually built telescopes with up 30x power magnification.

In January, 1610, Galileo observed what he called, ‘three fixed stars, totally invisible by their smallness.” Observations over subsequent nights revealed that the positions of the three stars were changing in a manner not consistent with geocentric cosmology. These observations triggered an astronomical revolution that still reverberates today.

The nature of Galileo’s discovery was such that many of his contemporaries refused to accept his findings. However, after his discovery was confirmed by Christopher Clavius, Galileo received a hero’s welcome when he visited Rome in 1611.

Galileo was also one of the first astronomers to directly observe a sun spot. The existence of sunspots directly challenged the geocentric notion of cosmic perfection and the work of Tycho Brahe.

Galileo died of heart palpations while under house arrest at his villa, near Arcetri, in 1642.


Biagioli, Mario (1993). Galileo, Courtier: The Practice of Science in the Culture of Absolutism. Chicago, IL: University of Chicago Press.

Blackwell, Richard J. (2006). Behind the Scenes at Galileo’s Trial. Notre Dame, IN: University of Notre Dame Press.

Brodrick, James, S. J. (1965) [c1964]. Galileo: the man, his work, his misfortunes. London: G. Chapman. Drake, Stillman (1990). Galileo: Pioneer Scientist. Toronto: The University of Toronto Press.

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