Born on February 15, 1564, in Pisa, Italy, Galileo Galilei was a mathematics professor who made pioneering observations of nature with long-lasting implications for the study of physics. He also constructed a telescope and supported the Copernican theory, which supports a sun-centered solar system. Galileo was accused twice of heresy by the church for his beliefs, and wrote books on his ideas. He died in Arcetri, Italy, on January 8, 1642.
Galileo Galilei was born on February 15, 1564, in Pisa in the Duchy of Florence, Italy. He was the first of six children born to Vincenzo Galilei, a well-known musician and music theorist, and Giulia Ammannati. In 1574, the family moved to Florence, where Galileo started his formal education at the Camaldolese monastery in Vallombrosa.
In 1583, Galileo entered the University of Pisa to study medicine. Armed with high intelligence and talent, he soon became fascinated with many subjects, particularly mathematics and physics. While at Pisa, Galileo was exposed to the Aristotelian view of the world, then the leading scientific authority and the only one sanctioned by the Roman Catholic Church. At first, Galileo supported this view, like any other intellectual of his time, and was on track to be a university professor. However, due to financial difficulties, Galileo left the university in 1585 before earning his degree.
Galileo continued to study mathematics, supporting himself with minor teaching positions. During this time he began his two-decade study on objects in motion and published The Little Balance, describing the hydrostatic principles of weighing small quantities, which brought him some fame. This gained him a teaching post at the University of Pisa, in 1589. There Galileo conducted his fabled experiments with falling objects and produced his manuscript Du Motu (On Motion), a departure from Aristotelian views about motion and falling objects. Galileo developed an arrogance about his work, and his strident criticisms of Aristotle left him isolated among his colleagues. In 1592, his contract with the University of Pisa was not renewed.
Galileo quickly found a new position at the University of Padua, teaching geometry, mechanics and astronomy. The appointment was fortunate, for his father had died in 1591, leaving Galileo entrusted with the care of his younger brother Michelagnolo. During his 18-year tenure at Padua, he gave entertaining lectures and attracted large crowds of followers, further increasing his fame and his sense of mission.
In 1604, Galileo published The Operations of the Geometrical and Military Compass, revealing his skills with experiments and practical technological applications. He also constructed a hydrostatic balance for measuring small objects. These developments brought him additional income and more recognition. That same year, Galileo refined his theories on motion and falling objects, and developed the universal law of acceleration, which all objects in the universe obeyed.
Galileo began to express openly his support of the Copernican theory that the earth and planets revolved around the sun. This challenged the doctrine of Aristotle and the established order set by the Catholic Church.
In July 1609, Galileo learned about a simple telescope built by Dutch eyeglass makers, and he soon developed one of his own. In August, he demonstrated it to some Venetian merchants, who saw its value for spotting ships and gave Galileo salary to manufacture several of them. However, Galileo’s ambition pushed him to go further, and in the fall of 1609 he made the fateful decision to turn his telescope toward the heavens. In March 1610, he published a small booklet, The Starry Messenger, revealing his discoveries that the moon was not flat and smooth, but a sphere with mountains and craters. He found Venus had phases like the moon, proving it rotated around the sun. He also discovered Jupiter had revolving moons, which didn’t revolve around the earth.
Soon Galileo began mounting a body of evidence that supported Copernican theory and contradicted Aristotle and Church doctrine. In 1612, he published his Discourse on Bodies in Water, refuting the Aristotelian explanation of why objects float in water, saying that it wasn’t because of their flat shape, but instead the weight of the object in relation to the water it displaced. In 1613, he published his observations of sunspots, which further refuted Aristotelian doctrine that the sun was perfect. That same year, Galileo wrote a letter to a student to explain how Copernican theory did not contradict Biblical passages, stating that scripture was written from an earthly perspective and implied that science provided a different, more accurate perspective. The letter was made public and Church Inquisition consultants pronounced Copernican theory heretical. In 1616, Galileo was ordered not to “hold, teach, or defend in any manner” the Copernican theory regarding the motion of the earth. Galileo obeyed the order for seven years, partly to make life easier and partly because he was a devoted Catholic.
In 1623, a friend of Galileo, Cardinal Maffeo Barberini, was selected as Pope Urban VIII. He allowed Galileo to pursue his work on astronomy and even encouraged him to publish it, on condition it be objective and not advocate Copernican theory. In 1632, Galileo published the Dialogue Concerning the Two Chief World Systems, a discussion among three people: one who supports Copernicus' heliocentric theory of the universe, one who argues against it, and one who is impartial. Though Galileo claimed Dialogues was neutral, it was clearly not. The advocate of Aristotelian belief comes across as the simpleton, getting caught in his own arguments.
Reaction by the Church
Church reaction against the book was swift, and Galileo was summoned to Rome. The Inquisition proceedings lasted from September 1632 to July 1633. During most of this time, Galileo was treated with respect and never imprisoned. However, in a final attempt to break him, Galileo was threatened with torture, and he finally admitted he had supported Copernican theory, but privately held that his statements were correct.
He was convicted of heresy and spent his remaining years under house arrest. Though ordered not to have any visitors nor have any of his works printed outside of Italy, he ignored both. In 1634, a French translation of his study of forces and their effects on matter was published, and a year later, copies of the Dialogue were published in Holland. While under house arrest, Galileo wrote Two New Sciences, a summary of his life’s work on the science of motion and strength of materials. It was printed in Holland in 1638. By this time, he had become blind and in ill health.
Death and Legacy
Galileo died in Arcetri, near Florence, Italy, on January 8, 1642, after suffering from a fever and heart palpitations. But in time, the Church couldn’t deny the truth in science. In 1758, it lifted the ban on most works supporting Copernican theory, and by 1835 dropped its opposition to heliocentrism altogether.
In the 20th century, several popes acknowledged the great work of Galileo, and in 1992, Pope John Paul II expressed regret about how the Galileo affair was handled. Galileo's contribution to our understanding of the universe was significant not only in his discoveries, but in the methods he developed and the use of mathematics to prove them. He played a major role in the scientific revolution and, deservedly so, earned the moniker "The Father of Modern Science."
In 1600, Galileo met Marina Gamba, a Venetian woman, who bore him three children out of wedlock: daughters Virginia and Livia, and son Vincenzo. He never married Marina, possibly due to financial worries and possibly fearing his illegitimate children would threaten his social standing. He worried the two girls would never marry well, and when they were older, had them enter a convent. His son’s birth was eventually legitimized and he became a successful musician.