Copernicus and Galileo Theory

Astronomy took a dramatic turn in the 16th century as a result of the contributions of the Polish astronomer Nicolaus Copernicus. Educated in Italy and made a canon (member of the clergy) of the Roman Catholic Church, Copernicus spent most of his life pursuing astronomy. His greatest contribution is entitled On the Revolution of Heavenly Bodies (1543), in which he analyzed critically the Ptolemaic theory of an Earth-centered universe and showed that the planetary motions can be explained much more simply by assuming that all the planets, including Earth, orbit the Sun. His ideas were not widely accepted until more than 100 years later.

The Italian astronomer Galileo ushered in a new era of science, one in which observations and experiments play the key role in testing models and hypotheses. Most historians believe that Dutch spectacle-maker Hans Lippershey invented the first telescope in the year 1608, but Galileo built one of his own in 1609, shortly after news of this invention reached him. Others had used telescopes to observe objects on Earth, but Galileo was the first to report astronomical observations, and his observations confirmed that Copernicus was right and that Ptolemy’s model of the planetary motions was wrong. Copernicus had predicted that if Venus orbits the Sun rather than Earth, Venus should go through phases just as the Moon does. Galileo discovered the phases of Venus. He also detected four moons orbiting Jupiter, which showed that not everything orbits Earth. One argument against the idea that Earth orbits the Sun was that the Moon would be left behind. Galileo’s observations clearly disproved that argument. After all, Jupiter’s moons were able to keep up with Jupiter.

Convinced that at least some planets did not circle Earth, Galileo began to speak and write in favor of the Copernican system. His attempts to publicize the Copernican system caused him to be tried by the Inquisition for heresy, and he was condemned to house arrest. Although he was forced to repudiate his beliefs and writings, Galileo and other Renaissance scientists showed that nature can be studied and understood through experiments and observations.