Buttressed by common sense, the ancient philosophers, and the church, the geocentric model of the universe seemed secure in its authority. The Ptolemaic theory, however, was not impervious to attack. In the 16th century, astronomers strained to make modern observations fit Ptolemy’s geocentric model of the universe.
Increasingly complex mathematical systems were necessary to reconcile these new observations with Ptolemy’s system of interlocking orbits. Nicholas Copernicus, a Polish astronomer, openly questioned the Ptolemaic system and proposed a heliocentric system in which the planets “including Earth” orbited the sun (“Helios”). This more mathematically satisfying way of arranging the solar system did not attract many supporters at first, since the available data did not yet support a wholesale abandonment of Ptolemy’s system. By the end of the 16th century, however, astronomers like Johannes Kepler (1571-1630) had also begun to embrace Copernicus’s theory.
Ultimately, Galileo’s telescope struck a fatal blow to the Ptolemaic system. But, in a sense, the telescope was also nearly fatal to Galileo himself. The Catholic Church, desperately trying to hold the Protestant heresy at bay, could not accept a scientific assault on its own theories of the universe. The pressures of the age set in motion a historic confrontation between religion and science, one which would culminate in 1633 when the church put Galileo on trial, forced him to recant his stated and published scientific beliefs, and put him under permanent house arrest.