Galilei, Galileo, generally called Galileo (1564-1642), an Italian astronomer, physicist, and mathematician. He ranks with Archimedes, Newton, and Einstein as one of the greatest scientists of all time. His discoveries, made with the crudest of equipment, were brilliant examples of scientific deduction. Galileo's studies of natural laws laid the groundwork for the experimental scientists who followed him.
Galileo constructed the first telescope used for astronomical observations; the observations he made supported Copernicus' theory that the sun is the center of the solar system. In physics, Galileo discovered the principles of motion followed by swinging pendulums, falling bodies, and flying projectiles. He invented the thermometer and a device called a hydrostatic balance for determining specific gravity.
Galileo was born at Pisa, the son of a musician who planned a medical career for him. He began studying medicine at the University of Pisa. According to legend, Galileo made his first major discovery at this time. He is said to have used his pulse to time the swinging of a suspended lamp in a cathedral; he found that, no matter how far the lamp swung, the timing was always the same. In later life Galileo established the fact that a free-swinging object, or pendulum, moves in uniform time intervals. Pendulum clocks are a common application of this principle.
Changing from the study of medicine to that of mathematics and natural science, Galileo conducted experiments on gravity that brought him to public attention. In 1589 he became a lecturer on mathematics at the University of Pisa, and began his studies of falling bodies. According to legend, he dropped objects from the Leaning Tower of Pisa to prove his theory that bodies fall at the same speed and with the same acceleration regardless of their weight and size. He also demonstrated that projectiles follow a parabolic path.
These discoveries were contrary to the teachings of the ancient Greek scientist and philosopher Aristotle, many of whose ideas had for centuries been accepted without question. Galileo aroused such opposition that in 1591 he was forced to resign from the university.
Success and Acclaim
The next year Galileo obtained a professorship in mathematics at the University of Padua, where he remained for 18 years. This was a period of successful research, acclaim, and prosperity for Galileo.
In 1609 Galileo received news of the invention, in Flanders, of a device that made distant objects appear larger. He immediately set out to build such a device for himself. The final result was a 32-power refracting telescope, with which he made a series of major discoveries. He found by observation that the moon shone only from reflected light; that the Milky Way was formed of a multitude of stars; and that the planet Jupiter was circled by several moons. His discoveries caused great excitement among astronomers, and he was besieged with orders for telescopes.
Conflict With the Church
In 1610 Galileo left Padua for Florence to become official mathematician and philosopher to Grand Duke Cosimo II de' Medici. By the end of the year his telescopic discoveries included the rings of Saturn, the phases of Venus, and sun spots. His observations clearly confirmed the theory of the Polish astronomer Copernicus that the earth and planets revolved around the sun. The Church, however, had accepted as conforming to the Bible the earlier idea of the planets and sun revolving around a stationary earth.
When Galileo visited Rome in 1611 he was given a welcome by Church officials befitting one of the greatest astronomers of all time, as he was then acknowledged to be. This gave him the courage to announce his support of the Copernican theory of the solar system.
Controversy flared. Although warned by the Church to avoid religious interpretation of his theory, Galileo attempted to prove it by quoting the Bible. He was told by the Church in 1616 to abandon the Copernican theory because it contradicted the Bible. In 1632, however, he published Dialogue on the Two Chief Systems of the World, in which he revived his argument in favor of the Copernican system. Galileo was then condemned by the Inquisition and forced to renounce his views. He lived his last nine years under house arrest.
In 1980 Pope John Paul II appointed a commission to reassess the Galileo case. In 1992 the pope, basing his decision on the commission's report, declared that the Inquisition erred in condemning Galileo.