Galilei, Galileo
1564–1642
Italian scientist

Galileo Galilei of Italy was the foremost scientist of the Renaissance. He made important contributions to the field of mechanics (the study of force and motion) and to the development of the scientificmethod. He is chiefly remembered, however, for his work in astronomy. Galileo, as he is known, did much to promote the heliocentric view of the universe, which holds that the Earth revolves around the Sun. This idea met with opposition from the Roman Catholic Church and from some other scientists, who saw it as conflicting with the Bible and with earlier ideas on the nature of the universe. Galileo spent his final years under house arrest, but his ideas spread, influenced other thinkers, and became part of the foundation of modern science.

Early Career. Galileo was born in Pisa, Italy. Eight years later his family moved to Florence, where Galileo received a classical* education at a nearby monastery. In 1581 Galileo enrolled as a medical student at Pisa's university, where he studied under several leading mathematicians of the day. After four years, Galileo left the university without a degree and began teaching mathematics privately in Florence. A few years later he became a professor of mathematics in Pisa. During his years there, Galileo wrote several volumes of notes on scientific subjects. One volume, which focused on topics such as gravity and bodies in motion, discussed a series of experiments that Galileo had performed in an effort to develop a set of laws of motion.

The death of Galileo's father in 1591 placed heavy financial burdens on the young scientist, who took a position at the University of Padua to improve his salary. He spent the next 18 years in Venice, a period that Galileo later described as the happiest of his life. During this time the scientist produced works on mechanics and kept notes and sketches of experiments he performed with pendulums, objects rolling on slanted surfaces, and thrown or falling objects.

A New Look at the Universe. During his early career, Galileo taught astronomy according to the theories of the ancient scholar Ptolemy. For centuries astronomers had relied on Ptolemy's model of the universe, which used an elaborate mathematical system to explain how the Sun, the Moon, and all the planets revolved around the Earth. A 1543 work by astronomer Nicolaus Copernicus, however, had presented a bold new view of the heavens, in which Earth and all the other planets revolved around the Sun. Galileo would come to be the leading champion of this new theory.

In 1609 Galileo heard that scientists in Holland had invented a new device called the telescope, which made it possible to view distant objects in greater detail than ever before. Galileo perfected the telescope for the study of heavenly bodies and turned his eyes toward the skies. He made startling discoveries, including new stars invisible to the naked eye, mountains on the surface of the Moon, and satellites orbiting the planet Jupiter. The following year he published these discoveries in a book called Sidereal* Messenger, which quickly made him the most famous astronomer in Europe. Galileo's discoveries earned him the patronage* of Cosimo II de' Medici, the grand duke of Tuscany (the region surrounding Florence). The scientist moved to Florence to serve as "mathematician and philosopher" to the grand duke. He also visited Rome, where he enjoyed the praise of fellow scientists.

Although Galileo had taught the theories of Ptolemy in Padua, his own observations and calculations convinced him that the Earth actually traveled around the Sun. He discussed this view with other scholars and referred to it in some of his writings. Although Galileo tried to argue that his evidence of the Earth's motion did not necessarily contradict the Bible, pressure against him began to mount. In early 1616 the church ordered Galileo not to "hold, teach, or defend" the view that the Earth moves and the Sun does not. Galileo agreed and avoided arrest. A few days later the church added Copernicus's revolutionary work to the Index of Prohibited Books.

In 1623 a new pope, Urban VIII, took office. At first, Urban VIII was sympathetic to Galileo, and most scholars believe that he granted the scientist some sort of permission to resume his studies of the Copernican system. By 1630 Galileo had finished his great work Dialogue Concerning the Two Chief World Systems. In this piece he compared the evidence for the systems of Ptolemy and Copernicus and came down heavily in favor of the Copernicans—in the process making those who held to the Ptolemaic system look rather foolish. Galileo argued that the Earth is similar to heavenly bodies in its motion and material. He disputed earlier proofs that the Earth is at rest and claimed that Earth was probably a planet that revolved around the Sun.

Trial and Later Years. To get a church censor to approve the publication of the Dialogue, Galileo added a statement to the text claiming that he meant it as a mathematical exercise only, not a proof of a moving Earth or a stationary Sun. Despite this precaution, the book's publication in 1632 landed Galileo in deeper trouble than he could have imagined. Pope Urban VIII was furious, possibly feeling that Galileo had broken an earlier promise to write on the topic without taking sides. The pope also thought that Galileo had ridiculed his own answer to the problem of the two world systems, which was that human intellect could not solve it. The church banned all further publication and sales of the Dialogue. It then summoned Galileo to Rome to be tried for teaching a theory that the church had condemned as contrary to Scripture.

A committee of ten cardinals tried Galileo. They found that he had taught and defended the opinions of Copernicus, although they could not be certain that he actually believed them—a more serious charge. To bring the matter to a close, the head of the committee offered to let Galileo plead that he had become carried away while writing and had defended the Copernican theory without meaning to do so. Galileo agreed to this position, but the pope was not satisfied. He made Galileo swear that he did not believe in the Earth's motion and that his former teachings were wrong. The church then pardoned Galileo, but confined him to his home and forbade him to write any more on Copernicanism.

During his forced retirement, Galileo continued his research into the science of mechanics. He published his results in 1638 under the titleThe Two New Sciences—the manuscript had been smuggled to Holland for printing. After 11 years of quiet house arrest, the leading scientist of his age died peacefully at his villa* at Arcetri. He was buried in the church of Santa Croce in Florence, where his remains lie near those of such other celebrated Renaissance figures as the artist Michelangelo Buonarroti and the author Niccolò Machiavelli.

(See alsoSciences, Physical; Scientific Instruments. )

* classical

in the tradition of ancient Greece and Rome

* sidereal

relating to the stars

* patronage

support or financial sponsorship

Righting a Wrong

Centuries after Galileo's death, the Roman Catholic Church admitted that it had been wrong to put him on trial and ban his work. The process began in 1820, when the church withdrew its condemnation of the Copernican system. Fifteen years later it removed Galileo's Dialogue from its list of forbidden books. In 1981 Pope John Paul II established a special commission to reexamine Galileo's trial. Its report, released in 1992, officially declared that religious authorities had misunderstood Galileo's teachings.

* villa

luxurious country home and the land surrounding it