Galilei, Galileo ................................ G
(1564–1642)
Italian physicist and astronomer, the first
scientist to rigorously apply mathematical
calculation to observation of the physical
world, thus inventing a revolutionary sci-
entific method that is still in use. Born in
Pisa, Galileo was the son of Vincenzo Ga-
lilei, a musician and amateur mathemati-
cian. His father’s calculations of musical
intervals and tonality inspired Galileo’s in-
terest in mathematics. Although he entered
a medical school at the University of Pisa,
Galileo did not complete the course of
study, turning instead to the field of math-
ematics and becoming head of the
university’s mathematics faculty at the age
of twenty-five, a reward for a paper he
wrote on the center of gravity in solid ob-
jects. While at Pisa he studied magnetism,
optics, and the phenomenon of the tides.
His invention of the hydrostatic balance
won him even wider renown in 1586, but
his innovative idea that the velocity of a
falling body was independent of its
weight—contradicting the classical teach-
ings of Aristotle—aroused a storm of op-
position. In 1592 he joined the faculty of
the University of Padua, where he taught
mathematics, astronomy, and physics; he
remained in this post until 1610.
In 1608, news of the invention of the
telescope in the Netherlands reached Italy.
Galileo soon fashioned one of his own that
allowed him to make important observa-
tions of the moon and the solar system. In
1610, he discovered Io, Europa, and Cal-
listo, three of the moons of Jupiter; four
days later he discovered the moon of
Ganymede. As these moons occasionally
disappeared, Galileo surmised that they
were regularly orbiting and disappearing
behind Jupiter; from this he concluded
that the traditional Ptolemaic, earth-
centered view of the universe was incor-
rect, as not all heavenly bodies revolved
around the earth. These observations made
Galileo a committed believer in the theory
of Nicolaus Copernicus, who placed the
sun at the center of the universe. To prove
his point, Galileo traveled to Rome, where
he demonstrated the telescope and allowed
church leaders and distinguished scholars
to view the satellites of Jupiter for them-
selves.Galileo Galilei. AP IMAGES.