Later that year Galileo turned his telescope toward
Saturn, observed its rings, and then turned toward
Venus. He discovered that Venus shows phases like
those of the Moon, which could only be possible if this
planet were to orbit the Sun, not the Earth. Galileo
had gathered convincing evidence to support the
Copernican theory of the solar system. Although the
religious authority at the time viewed this model as
antithetical to the Holy Scripture (in which the Earth
is perceived as lying at the center of the universe),
church leaders were tolerant of scholars who used
alternative theories in the guise of mathematical tools
for calculating the orbits of the planets. Galileo, unfor-
tunately, went further and later proclaimed in a private
communication that he was convinced that the theory
was a statement of physical reality. Unfortunately, the
letter was intercepted by the church, and for the 15
years that followed, the Catholic Church reviewed
Galileo’s work carefully and demanded that he follow
church teaching at all times. In 1632, Galileo
attempted to publish the text Dialogo (Dialogue) on
the theory of planetary motion, cleverly written so as
to never actually make the claim that the Copernican
system is the physical reality), but the church, feeling
that the boundary had been crossed, immediately
banned its sale, and tried Galileo for heresy. He was
found guilty and was placed under house arrest for the
remainder of his life. Galileo did, however, manage to
214 Galilei, Galileo
Galileo Galilei, an eminent scientist of the 17th century, was the
first to combine theory with experiment to understand dynamics.
He established that acceleration due to gravity is independent of
mass and that projectiles follow parabolic arcs. Galileo also
developed the telescope and made significant, and controversial,
astronomical observations. (Photo courtesy of Topham/The
Image Works)
Galileo managed to smuggle his controversial manuscript Dialogo
out of Italy, where its sale was banned, for publication in Holland.
(Photo courtesy of the Science Museum, London/Topham-HIP/The
Image Works)