Galileo Galilei

Galileo Galilei

Was an Italian astronomer, physicist, engineer, philosopher, and mathematician who played a major role in the scientific revolution of the seventeenth century. He has been called the “father of observational astronomy”, the “father of modern physics”, and the “father of science”. His contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the discovery of the 4 largest satellites of Jupiter (named the Galilean moons in his honour), and the observation and analysis of sunspots. Galileo also worked in applied science and technology, inventing an improved military compass and other instruments.

Galileo was born in Pisa, then part of the Duchy of Florence in nowadays Italy as the first of the six children of Vincenzo Galilei, a famous lute singer and music theorist and of his wife, Giulia Ammannati. Galileo’s full name was Galileo di Vincenzo Bonaiuti de Galilei. At the age of 8 years old, his family moved to Florence, but he remained two years in Jacopo Borghini’s care. Then, he was educated in the Camaldolese Monastery from Vallombrosa, 35 km southeast of Florence. Although he seriously considered becoming a priest, he entered the University of Pisa to study medicine at his father’s urging. He did not complete his medical degree, but instead studied mathematics. In 1589, he started to work at the chair of mathematics in Pisa. His father died in 1591 and Galileo took care of his younger brother, Michelagnolo. In 1592, he moved to the University of Padova, where he teachied geometry, mechanics and astronomy until 1610. During this period, Galileo made significant discoveries in both pure science (astronomy and cinematic movement) and applied science (strength of materials, improvement of the telescope). His multiple interests included the study of astrology, which in pre-modern disciplinary practice was seen as correlated to mathematics and astronomy.

In 1610, Galileo published an account of his telescopic observations of Jupiter’s satellites, using this observation to argue in favor of the Copernican heliocentric theory of the universe as an alternative to the dominant earth-centered theories of Ptolemaic and Aristotelian origin. The following year, Galileo visited Rome in order to present his telescope to the influential philosophers and mathematicians of the Jesuit Collegio Romano, and to let them see with their own eyes the reality of the four satellites of Jupiter. During his stay in Rome, he became a member of the Accademia dei Lincei.

In 1612, opposition to the heliocentric theory supported by Galileo Galilei increased. In 1614, the pulpit of the Basilica Santa Maria Novella, Father Tommaso Caccini (1574-1648) denounced Galileo’s opinions on the motion of the Earth, judging them as dangerous and close to heresy. Galileo Galilei went to Rome to defend himself against these accusations, but, in 1616, Cardinal Roberto Bellarmino personally handed Galilei an admonition not to advocate nor teach Copernican astronomy. Between 1621 and 1622, Galileo wrote his first book, “Il Saggiatore”, which was approved and published in 1623. In 1630 he returned to Rome to apply for a license to print the “Dialogue Concerning the two Chief world systems”, published in Florence in 1632. In October that year, however, he was ordered to appear before the Holy Office in Rome.

Galileo observed the Milky Way, previously considered to be a nebula, and found it to be a multitude of stars so close to each other that from the Earth they appeared to be clouds. He located many other stars too distant to be visible with the naked eye. Galileo observed “Neptune” in 1612, but did not realize it was a planet and didn’t gave much attention. It appears in his notebooks as one of the many other distant and weak stars. He noticed the double star Mizar in the Ursa Major in 1617. In “The Starry Messenger”, Galileo reported that the stars appeared to be simple bright flames unchanged in their appearance seen from the telescope, putting them in contrast to the planets that through the telescope were shown like disks. In his later writings, however, he described the stars as also being disks, whose size he measured. According to Galileo, stellar disk diameters typically measured a tenth of the diameter of the disc of Jupiter (five hundredth of the diameter of the Sun), although some were somewhat higher, others much smaller. Galileo also said that the stars are also some smaller suns that aren’t arranged in a spherical shell around the solar system, but at different distances from Earth. Brighter stars were considered  nearer suns and the weaker were farther. Based on this idea and based on the dimensions calculated by him for stellar discs, he calculated that the stars are at distances of a few hundred solar distances. These distances, although too small by modern standards, were much higher than planetary distances, and he used these calculations to argue the anti-Copernican theories which considered that the arguments of distant stars were absurd.

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