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To a great extent, the world in which we live today was freed from the superstition and bigotry of the Middle Ages by Galileo Galilei. Some of the others were Leonardo Da Vinci who preceded him, and Isaac Newton who succeeded him. This article is an account of some of Galileo’s achievements.

Galileo Galilei was born to a distinguished family at Pisa in Italy in 1564, and commenced his studies at the University of Pisa aged nineteen years. In accordance with Italian custom he is referred to by his first name Galileo


. It was intended by his father that he should study medicine, but he upset his lecturers by finding fault with much of the dogma of Aristotle, which was universally accepted as being correct. During his student years he discovered the principle of the pendulum by observing a lamp swinging from a roof of a church. He noted that whether the swing was larger or smaller due to gusts of wind, the period of each swing was the same. The period depended only on the length of the pendulum and was completely independent of mass. This was put into use by physicians for comparing pulse rates, and later in grandfather clocks following further work by Christaan Huygens one hundred years later.

He abandoned his medical studies and concentrated on natural philosophy and mathematics, including the writings of Archimedes.  He made such an impression, that at the age of twenty-five he was made the professor of mathematics at the university.

While at the University of Pisa, further to research by earlier scientists, he is said to have dropped two balls of different mass simultaneously from the top of the Leaning Tower. Both are said to have hit the ground at the same time, putting paid to the theory of Aristotle concerning falling bodies: We see the same weight or body moving faster than another for two reasons, either because there is a difference in what it moves through, as between water, air, and earth, or because, other things being equal, the moving body differs from the other owing to excess of weight or of lightness.

However, given the impossibility of measuring time to the millisecond in those days, Galileo’s experiment was probably theoretical in his mind only.



Because of attacks made on his anti-Aristotelian views in Pisa, Galileo then moved to the University of Padua as professor of mathematics in 1592 , where among other discoveries, he developed the Galilean Telescope. He had heard of the invention in Europe of a telescope which could magnify objects three times.  He immediately experimented, and by using a combination of a convex and a concave lens, in 1609 he developed a telescope which could magnify objects twenty times. His friend the great German astronomer Johannes Kepler, later developed a telescope with a greater magnification by using a combination of two convex lens, which however produced and inverted image. This is able to be corrected by the use of a third convex lens as the eyepiece, or by the use of an additional concave mirror.



This is when it all started to go pear shape for Galileo. He was influenced by the writings of the Prussian canon and mathematician, Nicolaus Copernicus,who in the previous century had written that the earth revolved about the sun, and by the writings of the Dominican priestGiordano Bruno, who described an infinite universe in amazing detail. Bruno, who also published anti-religious writings, was condemned by the Italian Inquisition and executed on the order of Pope Clement VIII. The charges included his assertion of the plurarity of worlds. His execution, which took place in 1600,involved being suspended upside-down naked and then burned to death.


Making use of his telescope, Galileo observed the Milky Way, the moon with its valleys and mountains, and moons orbiting about Jupiter. He became convinced that Copernicus was correct and following his appointment in 1610 as the Philosopher and First Mathematician to the Grand Duke of Tuscany, published his Letters on the Solar Spots in 1613 which showed that by the transit of the sun spots which he observed, the sun was continually turning on its axis. He made many enemies including the Jesuits and those who adhered to Aristotle and Claudius Ptolemy, a Roman mathematician and astronomer who in the second century AD prepared a geocentric model, having the earth at the centre.


In early 1616, the Holy Office appointed theologians known as Qualifiers to assess the propositions advanced by Galileo that the sun was the centre of the world and immovable, and that the earth is not the centre of the world nor immovable. The Qualifiers found that both propositions were foolish and absurd, formally heretical, and expressly contradict the doctrine of Holy Scripture in many passages

Following the findings of the Qualifiers, Galileo was summonsed to appear before the Jesuit Cardinal Bellarmine in Rome, which occurred later that year.He was commanded in the name of Pope Paul V and the Holy Office to relinquish the opinion that the sun is the centre of the world and that the earth moves around it, and not to speak or write about such heliocentric theory. Galileo consented.


Surprisingly, much of the Christian theology, even up until today, is based on that of the ancient Greek philosophers, including Plato and his student Aristotle. The most prominent of the Christian philosophers was Thomas Aquinas who wrote his massive Tome Summa Theoligica containing some 3,500 pages which was published in the late 1400s, which was the century before Galileo.



In the Summa, which contained the Christian theology up until that time, Aquinas expressed his view as to the world in what is known as the geocentric system, which has the earth as its centre, with the sun, moon, stars and planets revolving around the earth, as follows:… as in astrology the theory of eccentrics and epicycles(geocentrics)is considered as established, because thereby the sensible appearances of the heavenly movements can be explained; not, however, as if this proof were sufficient, forasmuch as some other theory might explain them ...This reflected the writings of Aristotle and Ptolemy, whose treatise Almagest on the geocentric system was accepted as true for over 1200 years




This view of Aquinasechoes many biblical statements in support of geocentricity, such as: The earth is vast, and the heaven is high, and the sun is swift in its course, for it makes the circuit of the heavens and returns to its place in one day.1 Esdras 4:34

Following the 1616 injunction (and there is some doubt as to it was ever given, but was maliciously planted in Galileo’s file by one of his enemies), Galileo kept a low profile until 1623 when Pope Urban VIII replaced Paul V. Urban’s private secretary wrote to Galileo from Rome and urged him to resume publishing the results of his observations and research.


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Following audiences with, and encouragement from Pope Urban who had also attended the University of Pisa, Galileo completed writing Dialogue Concerning the Two Chief World Systems in 1629. The book described a fictitious debate between three men as to which word system was correct. Salviati (portraying Galileo) argues tor the heliocentric system; Sagredo is an undecided good listener; and Simplicois a committed defender of the geocentric system.

Galileo submitted the book to the Vatican for approval to publish, where the chief licenser NiccoloRiccardidemanded that Galileo revise the preface and conclusion, which Galileo did. Riccardi finally gave permission and the book was published in 1632 and sold out becoming a sensation. The Jesuits then intervened and persuaded Pope Urban that Simplico was a parody of himself. Publication was suspended, and Urban set up a commission of investigation. Following the commission’s report which contained proposed indictments against Galileo, the matter was referred to the Inquisition. Later that year Galileo was summonsed to appear in Rome before the Inquisition, and despite his age and frail health travelled to Rome.


Galileo was tried before the Inquisition of Cardinals in an extremely convoluted manner over a period of three months. During the trial he was questioned before being charged, and was found guilty of vehement suspicion of heresy. He wasshown the instruments of torture in order to decide whether he had intended to promote heliocentrism in the Dialogue as being true, in which case he would be in risk of the death sentence for heresy, as befell Bruno. Under this coercion, Galileo signed a document in which he admitted that Ptolemy was correct and Copernicus was incorrect. He was sentenced to life imprisonment, which next day was changed to house arrest on his farm for life.

To a degree, Galileo was incorrect. He believed that the sun was the fixed centre of the universe, whereas it is just the fixed centre of our solar system. He also believed that the sun does not move, whereas it orbits the centre of our galaxy, the Milky Way.



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