Cheryl O'Shea, age 13, of Danville, I11., for his question:
WHO WAS GALILEO?
Galileo was an Italian physicist and astronomer who, with the German astronomer Johannes Kepler, initiated the scientific revolution that flowered in the work of the English physicist Sir Isaac Newton. Galileo's full name was Galileo Galilei and he lived from 1564 to 1642.
In physics, Galileo discovered the laws of falling bodies and the motion of projectiles. In the history of culture, he stands as a symbol of the battle against authority for freedom of inquiry.
In the field of astronomy, Galileo's main contributions were the use of the telescope in observation and the discovery of sunspots, lunar mountains and valleys, the four largest satellites of Jupiter and the phases of Venus.
Galileo's most valuable scientific contribution was his founding of physics on precise measurements rather than on metaphysical principles and formal logic.
Galileo entered the University of Pisa in 1581 to study medicine, but soon turned to philosophy and mathematics. He became a professor of mathematics at Pisa in 1589 and three years later he was appointed to the chair of mathematics at the University of Padua.
At Padua, Galileo invented a calculating "compass" for the practical solution of mathematical problems. He turned from speculative physics to careful measurements, discovered the law of falling bodies and of the parabolic path of projectiles, studied the motions of pendulums and investigated mechanics and the strengths of materials.
In 1609 Galileo heard that a spyglass had been invented in Holland. He improved the idea and came up with a telescope that was about as powerful as a modern field glass.
A few months later Galileo built a telescope of 20 times magnification, with which he discovered mountains and craters on the moon and saw that the Milky Way was composed of stars.
Galileo's father, Vincenzio Galilei, played an important role in the musical revolution from medieval polyphony to harmonic modulation. Just as Vincenzio saw that rigid theory stifled new forms in music, so his eldest son came to see Aristotelian physical theology as limiting scientific inquiry.
Galileo rejected the Aristotelian theory that assumed all planets circled a fixed earth. Instead, he preferred the Copernican theory that said the planets revolved around the sun. He was scorned by many for his beliefs.
But Galileo gained fame and won appointment as the court mathematician at Florence. He was thereby freed from teaching duties and had time for research and writing.
In 1632 Galileo published his masterpiece, "A Dialogue on the Two Principal Systems of the World." The Holy Office, or inquisition, immediately called him to appear before it. After a long trial, Church officials forced him to say that he gave up his belief in the Copernican theory, and sentenced him to an indefinite prison term. Instead of imprisoning Galileo, they confined him to his villa in Florence.
He spent his last years writing on the laws of force and motion.