14 Jupiter’s Moons
In one night’s viewing of the moon’s surface through his telescope, Galileo proved Aristotle wrong—again. The last time Galileo’s observations had contradicted Aristotle’s
teachings, Galileo had been fired from his teaching position for being right when he proved
that all objects fall at the same rate regardless of their weight.
Galileo next aimed his telescope at Jupiter, the biggest planet, planning to carefully
chart its motion over several months. Through his telescope (the name is a combination of
the Greek words for “distant” and “looking”) Galileo saw a magnified view of the heavens
no human eye had ever seen. He saw Jupiter clearly, and, to his amazement, he found moons
circling the giant planet. Aristotle had said (and all scientists believed) that Earth was the
only planet in the universe that had a moon. Within days, Galileo discovered four of Jupiter’s moons. These were the first discovered moons other than our own.
Aristotle was wrong again.
Still, old beliefs do not die easily. In 1616 the Council of Cardinals forbade Galileo
ever again to teach or promote Copernicus’s theories. Many senior church officials refused
to look through a telescope, claiming it was a magician’s trick and that the moons were in
the telescope.
When Galileo ignored their warning, he was summoned to Rome by the Church’s
all-powerful Inquisition. A grueling trial followed. Galileo was condemned by the Church
and forced to publicly recant his views and findings. He was placed under house arrest for
the rest of his life, dying in 1640 without hearing even one voice other than his own proclaim that his discoveries were true. The Church did not rescind the condemnation of Galileo and his discoveries until October 1992, 376 years after they incorrectly condemned him.
Fun Facts: Galileo would have been astonished to learn that Jupiter resembles a star in composition. In fact, if it had been about 80 times more
massive, it would have been classified as a star rather than a planet.
More to Explore
Aldrain, Buzz. Galileo for Kids: His Life and Ideas. Chicago: Chicago Review Press, 2005.
Atkins, Peter, Galileo’s Finger: the Ten Great Ideas of Science. New York: Random
House, 2004.
Bendick, Jeanne. Along Came Galileo. San Luis Obispo, CA: Beautiful Feet Books, 1999.
Drake, Stillman. Galileo. New York: Hill and Wang, 1995.
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