Galileo Galilei

Galileo Galilei (1)

Galileo Galilei(3) "Father of Modern Science", was born in Pisa, Italy on February 15, 1564. Galileo entered the world at a time when astronomers had discovered very little about the universe; however, the findings he made in his lifetime caused a new wave of scientific achievement. Famously known for using scientific methods and his refracting telescope, Galileo was able to find important details about the nature of our Solar System(13). These details were carefully recorded by Galileo and they led to his belief in heliocentrism(15), which suggests that the Earth revolves around the Sun. Galileo's agreement with this Copernican System(16) of heliocentrism was unorthodox for the time period, and it would later cause great controversy between Galileo and the Catholic Church(17).

Early Life
Portrait of Galileo (11)

Galileo Galilei was the eldest son in his family, as he had four sisters and two younger brothers. Galileo's father, Vincenzio Galilei(16), was well educated, and as a result, he was very influential in the education that Galileo received. For example, after moving from Pisa to Florence, Italy in 1572, Galileo received schooling at a Jesuit school. He was only ten years old when he moved to Florence; yet, after his experience at school, Galileo began working towards joining the priesthood. When Vincenzio Galilei realized that his eldest son had been working towards the priesthood, he encouraged Galileo to change career paths. Vincenzio suggested that Galileo leave the monastery immediately in order to study medicine. (2) Due to his father's advice, Galileo began studying medicine at the University of Pisa(12) in 1581. Galileo was only seventeen at the time; however, despite his young age, Galileo quickly displayed interest in science and mathematics. Galileo explained that he was interested in studying these subjects as he believed that it would allow him to acquire knowledge of nature.(3)

Galileo was known to be popular while studying at the University of Pisa, as he was very outgoing and enjoyed arguing in dispute of Aristotle's(18) work in class. This argumentative behavior would have given Galileo attention, as Aristotle's work was widely accepted in the Renaissance(19) period. (7) Thus, despite the fact that he did not graduate from the University of Pisa, Galileo was able to discover his main passion in life, and he had a very successful three years. In his three years at Pisa, Galileo had expanded his knowledge of the universe and began to believe in Copernicanism, or an Earth centered universe. (2) Also, after leaving the University of Pisa, Galileo was hired to be a mathematician at the University of Padua.(17) The University of Padua was another important stepping stone in Galileo's early life, as he stayed here for eighteen years. In addition, it was here that he met Marina Gamba(16), who was Galileo's mistress for ten years. Galileo would eventually have three children with Marina Gamba, although he is not listed as the father on their records. Despite the fact that Galileo never married Marina Gamba, historians suggest that she was very influential in Galileo's life, and their relationship remained strong for many years.(7)

***While studying at the University of Pisa, Galileo's outspoken personality earned him the following name: "The Wrangler"

Scientific Discoveries

During Galileo's time at the University of Pisa, he developed some important ideas about the nature of the Solar System. For instance, after reviewing the work of Aristotle, Galileo discovered that time was linked to the motion of objects. During his research regarding time and motion, Galileo created an incline plane(16) in order to slow the process of moving objects. In addition, Galileo was able to expand on Aristotle's concepts of the elements of Earth by adding that the heavens were made of material called quintessence(16). Galileo also argued against a number of Aristotle's ideas, such as, Aristotle's notion of falling objects. In arguing against Aristotle's belief of falling objects, Galileo pronounced that objects would fall at the same rate when they were unaffected by air resistance. Moreover, his rejection of these well-known Aristotelian notions caused some people to look down upon Galileo as an astronomer.(7)

One important discovery that Galileo is credited for is the creation of the first thermoscope(16) in 1600. This was the first instrument that could measure temperature, and in 1612, the first thermometers(16) were used in practice. Soon after this period of time, Galileo made some critical observations in regards to the motion of objects within the solar system. However, one negative theory that Galileo is remembered for is his teaching of Ptolemy's(16)theory. This is because Ptolemy's theory involved an Earth centered solar system, with the other planets revolving around the Sun. We know today that Ptolemy's concept of the Solar System is incorrect, and it is unfortunate that Galileo is linked to teaching this approach. However, Galileo was being payed to teach this theory, and many historians believe that Galileo did not fully accept Ptolemy's theory. This argument seems to be plausible, as we know that Galileo was very open about his strong belief in Copernicism.(7)

In 1609, Galileo was able to adjust and improve the telescope,(16) which increased his popularity greatly. Galileo's improvement of the telescope was revolutionary for the time period, and the magnification enabled him to see the Moons of Jupiter(16) and the Mountains on Earth's Moon(16). (3) Galileo proposed that the Moon's mountains were greater than four miles in height, which led him to believe that the Moon had larger mountains than those of Earth. Galileo's improvement of the telescope also allowed him to take a much closer view of the stars than anyone had done before. For instance, Galileo is said to have made critical observations of Saturn(24) and Venus(20). However, Galileo seemed to be confused by Saturn (due to its disappearing Moons), so he spent a long time observing Saturn and Venus.(7) Many of his telescopic discoveries were published in Galileo's, The Starry Messenger(21) which came out in 1610. The Starry Messenger was an important text as it displayed Galileo's achievements and increased his popularity as an astronomer.(3) However, it should be noted that Galileo's telescope had a very small field of view. Therefore, despite the fact that Galileo's telescope allowed him to enlarge objects up to 20 times, the most he could see of the Moon was roughly one-half of its entire diameter.(4)

***While watching the Moons of Saturn, Galileo reported that the Moons would sometimes disappear. Scientists today believe that this may have been caused by Saturn's rings being edge onto Earth, where they are not visible for a period of time. This only happens about once every fifteen years!(7)

Galileo's Telescope (8)

The YouTube video below was found at (14)


Between 1611 and 1615, Galileo became focused on two problems due to encounters that he had come across in his studies. Galileo became concerned with floating bodies (3) as well as the appearance of sunspots (3).(2) Galileo believed strongly in Copernicanism and he felt that it was his duty to convert as many people to the Copernicanism as possible. Galileo thought that Copernicanism was the only plausible option for the Earth, as the Earth's motion was the clear cause of the tides(16). Galileo expresses his reasoning behind the proof that Earth tides are linked to the Copernican System in On the Ebb and Flow of the Tides(16). This text expressed Galileo's belief in Copernicanism, which unfortunately caused many people to reject Galileo's work. In addition, Galileo's heartfelt duty to teach Copernicanism would eventually lead to controversy with the Catholic Church.(3)

***Rather than writing his texts in the manner that we are familiar with today, Galileo sometimes chose to use conversations between three different people.(7)

Renaissance Astronomy (9)

Galileo's Trial (6)


Soon after Galileo published Dialogues Concerning the Two Great World Systems(22) in 1632, the Catholic Church banned it's sale and Galileo was forced to go on trial. Specifically, Galileo was charged for heresy (17) in teaching others that the Sun was the center of the universe. Thus, in 1633, Galileo pleaded guilty, but was still condemned to house arrest. In Galileo's condemnation, the Catholic Church also stated that Galileo would be forced to live in isolation until his death (1642).(3)

After being convicted, Galileo was forced to take back his scientific beliefs. It is believed that he stated the following:

"I, swear that I have always believed, do now believe and, with God's help shall believe hereafter, all which is held, preached and taught by the Holy Catholic and Apostolic Church. ... I must altogether abandon the false opinion that the Sun is the center of the world and immovable, and that the Earth is not the center of the world and moves and that I must not hold, defend or teach in any way whatsoever, verbally or in writing, the said false doctrine ..." (7)

***According to popular legend, it is stated that after Galileo was condemned he said, "Eppur si muove, " which means, "and yet the it (the Earth) does move."(7)

End of Life

After Galileo's condemnation in 1633, Galileo began working on his final work entitled, Discourses and Mathematical Demonstrations Concerning Two New Sciences(23). Unfortunately, around the same time that Galileo began writing his final book, he fell ill and his daughter, Maria Celeste(16) passed away in 1634. He was deeply saddened by the death of his daughter and his health soon took a turn for the worst. As a result of his health, he lost his eyesight in 1637, and historians suggest that he petitioned the Catholic Church to release him from isolation due to medicinal reasons. The Catholic Church denied this petition and Galileo was forced to remain in isolation for the remainder of his life.(7) Also, because Galileo had been condemned from expressing his belief in Copernicism, his final book would not have been allowed to be published in Italy. However, despite this ruling, Discourses and Mathematical Demonstrations Concerning Two New Sciences was illegally taken out of Italy and published in Holland in 1638, right before Galileo's death. Galileo died of health complications in 1642, and due to his condemnation, he was buried in an unknown location until 1737.(3)

***Almost 300 years after Galileo's death, the Catholic Church acknowledged the truth in Galileo's work in 1992.(7)

Galileo Cartoon (10)

By: Melanie Albert

Works Cited

*Link to Famous Astronomers