Galileo Galilei (1564-1642)

The Church and Copernicus | Galileo Galilei | Tycho Brahe and Johannes Kepler | Isaac Newton

Overview and Beginnings

Galileo Galilei was an Italian mathematician and philosopher. He is possibly the most famous of all Renaissance scientists, and he is often considered the founder of modern astronomy. The reason for this was his perfection of the refracting telescope, which was invented in Holland in the very early 1600's. Galileo heard of it, and built a home-made model in 1609.

With it, Galileo was able to see the four major Jovian moons (now called the Galilean Satellites in his honor)*. Besides these, which rank among the most important of his observations, Galileo drew detailed diagrams of the moon, observing valleys and mountains and craters. He also looked at the sun and observed dark blemishes on its surface, which are now called sunspots. From the movement of these, he was able to determine that the sun has a rotation period of about one month.

These observations of celestial bodies, published in a book called Sidereus Nuncius (The Starry Messenger) in 1610, were the foundations of his troubles with the Catholic Church.

*Galileo originally named the four moons of Jupiter the "Medician Stars, " in honor the ruling family of his province in Italy at the time. After all, it's not a bad idea to name a celestial object after one of your biggest sources of funding.

Resistance Is Futile

Besides the geocentric - Earth-centered - model of the universe, the Church held that celestial bodies, such as the sun and moon, were prefect. Galileo's observations of spots on the sun and varied terrain on the moon were in direct opposition to this doctrine.

Besides this, Galileo viewed the Jupiter system as a small model of our solar system, and became convinced of the Copernican heliocentric system. Making his argument public, Galileo was ordered by the Church in 1616 to retract his claims that the Earth rotated around the sun.

However, Galileo did not, and in 1632 published the book Dialogue Concerning the Two Chief World Systems. In it, he presented arguments for the Copernican view as a discussion with a character who is a proponent of geocentricity. Time and again in the book, the Copernican believer is shown to be well-founded in logic and observation. Not only did the book present again this forbidden view, but it was also published in Italian which made it very widely available to the general public.

Galileo was again brought before the Church, and made to retract his claims upon threat of torture. He was also placed under house arrest in 1633 through the end of his life, four years later on January 8, 1642. His book, however, was brought to a press in Holland where it was published and referred to as Two New Sciences. In 1992, the Catholic Church reconsidered the Inquisition's findings, and removed Galileo from any wrongdoings.

In honor of Galileo, the Galileo spacecraft was launched in 1989 by NASA in his honor. The craft's mission was to explore Jupiter and its moons, just as its namesake had over almost 300 years earlier.