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Like Aristotle and Copernicus, Galileo Galilei learned from observing and measuring what
he saw. Galileo lived in Pisa, a city on the northwestern coast of the Italian peninsula.
In 1583, when Galileo was nineteen-year-old, he observed a priest swinging an altar lamp.
No matter how wide the swing of the lamp, it seemed the time it took to move from one
end to the other was always the same. Galileo had discovered what scientists today call
isochronism, and his observations led to the development of the pendulum clock.
Galileo heard stories of a tool that used curved pieces of glass to magnify distant
objects. The Italian scientist was unable to purchase the instrument we now call a telescope,
so he built a telescope on his own. When Galileo observed the heavens, he made several discoveries
that differed with Aristotle’s theory of an earth centered universe.
In Galileo’s time, many people believed in a geocentric universe where all heavenly
objects revolved around the earth. Galileo’s discovery of moons orbiting Jupiter disproved
that theory. While Galileo’s discovery did not prove the earth travels around the sun,
it disagreed with the way many people interpreted the Christian Bible. In 1616 Pope Paul V,
the leader of Galileo’s Catholic Church, commanded that the scientist never again “defend
or hold” the idea of a heliocentric universe. Though he was a very religious man, Galileo
continued to make new discoveries and continued to promote Copernicus’ theory of a universe
that revolved around the sun. Sixteen years later, Galileo went on trial for heresy. Heresy
is an opinion or belief that disagrees with the official position of the church. Galileo
was found guilty of teaching that the sun is the motionless center of the universe.
He was sentenced to house arrest for the remaining nine years of his life. Galileo accepted his
sentence, but he continued to write and study from his home.