Galilei, Galileo

Italian Astronomer, Mathematician, and Physicist 1564-1642

Galileo Galilei (commonly known as Galileo) was a founder of modern physics and modern astronomy. He was born in Pisa, Italy, in 1564, and was a professor from 1592 through 1610 at Padua, which was part of the Venetian Republic. While in Pisa, he noticed a chandelier swinging in the cathedral and developed the physical law that shows that pendulums of the same length swing in the same time interval. Using a pendulum for timing, he experimentally worked out how objects accelerate while falling. In these experiments, he rolled objects down an inclined plane; the traditional story that he dropped weights from the Leaning Tower of Pisa was a myth.

In 1609 Galileo heard of a device that existed that could magnify distant objects. Using his experimental abilities, he ground lenses and assembled a telescope. He demonstrated its possibilities for aiding commerce byshowing Venetian nobles that they could see ships approaching farther out than ever before. Starting that same year, Galileo also turned his telescope toward the sky. He subsequently discovered that the Moon had mountains and craters on it, that Jupiter had moons orbiting it, and that Venus went through a complete set of phases. These observations indicated that Greek philosopher Aristotle's (384-322 B.C.E.) view of the universe as unchanging and perfect was not true, and Galileo endorsed Polish astronomer Nicholas Copernicus's (1473-1543) idea that the Sun instead of Earth is the center of the solar system. Galileo's book Sidereus nuncius (The starry messenger; 1610) brought his discoveries to a wide audience.

Soon Galileo discovered sunspots, showing that the Sun is not a perfect body. But a controversy with a Jesuit astronomer over who discovered sunspots set the Roman Catholic Church against him. In 1616 the Church's Inquisition warned him against holding or defending Copernicus's ideas. To get his agreement, they showed him instruments of torture.

Galileo was relatively quiet until his book Dialogo sopra i due massimi sistemi del mondo (Dialogue on the two great world systems) was published in 1632. It was written in his native Italian instead of the scholarly Latin, to spread his discussion widely. The Inquisition then convicted him of teaching Copernicanism and sentenced him to house arrest. But even under those conditions, and the blindness that came on, he continued his scientific work. He died in Florence in 1642. In 1992 Pope John Paul II agreed that Galileo was correct to endorse Copernicanism, though Galileo was not pardoned.

Astronomy, History of (Volume 2);; Copernicus, Nicholas (Volume 2);; Jupiter (Volume 2);; Moon (Volume 2);; Religion (Volume 4);; Saturn (Volume 2);; Venus (Volume 2).

Machamer, Peter, ed. The Cambridge Companion to Galileo. Cambridge, UK: Cambridge University Press, 1998.

MacLachlan, James H. Galileo Galilei: First Physicist. New York: Oxford UniversityPress, 1987.

Reston, James, Jr. Galileo: A Life. New York: Harper Collins, 1994.

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