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GALILEO GALILEI (1564 - 1642)

Galileo was born near Florence, Italy. His family moved to Pisa when he was two years old and Galileo lived there until the age of ten. When he returned to Florence he was first tutored by Jacopo Borghini and then sent to Camaldolese Monastery, about 33km from Florence. Galileo enjoyed the solitary life of the monks and wanted to join the order. His father, however, had other ideas; he wanted Galileo to study medicine. Eventually Galileo did attend Pisa University as a medical student but his heart was not in his medical studies. He preferred to study mathematics and went to all the mathematics lectures. One summer, his mathematics tutor joined Galileo and his family and persuaded his father to allow Galileo to swap courses.

In fact, Galileo dropped out of university and started teaching mathematics in Sienna. He was noticed by a lot of influential people in the academic world and, after giving some lectures at Florence University, he was offered a job teaching mathematics at the University of Pisa. He spent three years in Pisa but moved on to the University of Padua when his father died because the new post offered more money and he now had to support his family.

In 1609 Galileo first learnt about the telescope in letters from one of his friends. With very little information to go on, he made his own telescope, even making the lenses to use in it. Galileo telescope magnified around x30. He called it an Aperspillum. The Aperspillum was demonstrated in Venice and, even though Galileo had admitted the Apersillum was not his invention; the Venice State gave Galileo a large increase in salary for the right to make more.


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Galileo started pointing his telescope towards the skies in 1609. He saw Moon craters, stars in the Milky Way and four of the larger of Jupiter’s moons. He wrote a book about his observations called Starry Messenger and this publication made him famous. In 1610 he turned his telescope to Venus. His observations told him that Venus had phases, just like the Moon. He realised that this could only happen if Venus orbited the Sun. This meant that Copernicus and his heliocentric model were correct.

The Church had adopted the geocentric theory, which says that the sun and the other planets revolve around the Earth. To openly advocate the heliocentric theory was considered heresy. Galileo, however, was on good terms with Pope Urban VIII and thought that it would be alright for him to publish his book, Dialogue Concerning the Two Chief Systems of the World - Ptolemaic and Copernican. This book had been started in 1624 but it was not published until 1632. The book is a dialogue between a geocentric theory supporter and a heliocentric theory supporter. The dialogue makes the geocentric supporter, hence the Church, look silly.

The Inquisition banned the book and Galileo was put on trial in Rome. He was given a life sentence but, because of his ill health, this became a house arrest. It basically meant that, for the rest of his life, he could not do anything without the Inquisition watching him.

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