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Throughout his life Galileo would provide some of the most compelling arguments in favor of the heliocentric model; though this brought him endless trouble in his lifetime, he was vindicated by all subsequent investigators. The beginnings of Galileo's astronomical studies were quite dramatic: in 1604 a ``new star'' (a supernova--an exploding star) was observed,. Galileo demonstrated that this object must lie beyond the Moon, contradicting the Aristotelian doctrine which claimed that the region beyond the Moon was perfect and unchanging. Yet here was a star that was not there before and would soon disappear!

A few years later he learned about the discovery of the telescope. He quickly realized its potential as a tool in astronomical research, and constructed several of them (Fig. 4.6), which he used to investigate the heavens.


Figure 4.6: One of Galileo's telescopes  
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The first object which he studied with his telescope was the Moon of which he made many drawings (Fig. 4.7) some of which are quite accurate. He found that the surface of the Moon was heavily scarred, and identified some of the dark features he observed as shadows. The Moon was not exactly spherical and hardly perfect.


Figure 4.7: Galileo's drawings of the Moon.  
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Galileo was the first person to discover that Venus, like the Moon, shows periodic phases (Fig. 4.8). The simplest explanation is that this planet goes around the sun in accordance with the Copernican system. Galileo's astronomical observations were later verified by the Jesuit mathematicians of the Collegio Romano (although they did not necessarily agree with Galileo's interpretation!).


Figure 4.8: Galileo's drawings of the phases of Venus.  
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But the most dramatic of Galileo's astronomical discoveries was that of Jupiter's satellites (1610) [*]. He found that Jupiter was surrounded by a swarm of bodies that circled it and not Earth! These satellites, together with Jupiter, formed a mini-version of the Copernican model of the solar system with Jupiter taking the place of the Sun and it's satellites the places of the planets. All this was in blatant contradiction of the Aristotelian model; any remaining doubts which he might have had in his belief of the heliocentric model vanished.

In 1613, in a book on sunspots, Galileo openly declared the Earth to circle the Sun. But by then the Church was getting worried about these ideas: in 1616 Pope Pius V declared the Earth to be at rest and labeled the heliocentric model heretical, Copernicus' magnum opus was black-listed (where it remained until 1822!), and Galileo was called to Rome and told not to defend Copernicus' ideas.

In 1632 Galileo published his book on the Copernican and Ptolemaic systems Dialogue Concerning the Two Chief Systems of the World (in Italian so everyone could understand it). This was originally condoned by the Church, but the Pope Urban VIII had a change of heart and forbade the distribution of the book. Galileo was summoned to appear before the Roman Inquisition where, in a penitential garb and on one knee, he was made to swear on the Bible that he

``...abjured, cursed, and detested the error and heresy that the Sun is fixed and the Earth moves''

and that he would no longer support this idea in any manner. He was put under house arrest and was made to recite the seven penitential psalms weekly for three years. This, of course, did not change the fact that the planets do move around the sun, but it embittered Galielo's last years.

next up previous contents
Next: Galileo and the Inquisition Up: Galileo Galilei Previous: The motion of projectiles

Jose Wudka