Galileo Galilei: Education and Scientific Contributions

Galileo Galilei, an Italian astronomer, physicist, engineer, and polymath, made profound contributions to science. Born in Pisa on February 15, 1564, and died on January 8, 1642, in Arcetri, near Florence. Galileo's work spanned diverse fields, including the study of speed and velocity, gravity and free fall, the principle of relativity, inertia, projectile motion, and applied science and technology. He is often called the “father of modern astronomy” and the “father of modern physics”.

Early Life and Education

Galileo di Vincenzo Bonaiuti de' Galilei was the first of six children born to Vincenzo Galilei, a lutenist, composer, and music theorist, and Giulia Ammannati, the daughter of a prominent merchant. Three of Galileo's five siblings survived infancy. The youngest, Michelangelo, also became a lutenist and composer. In his middle teens Galileo attended the monastery school at Vallombrosa, near Florence, and then in 1581 matriculated at the University of Pisa, where he was to study medicine. However, he became enamoured with mathematics and decided to make the mathematical subjects and philosophy his profession, against the protests of his father. Galileo then began to prepare himself to teach Aristotelian philosophy and mathematics, and several of his lectures have survived. In 1585 Galileo left the university without having obtained a degree, and for several years he gave private lessons in the mathematical subjects in Florence and Siena.

Although Galileo seriously considered the priesthood as a young man, at his father's urging he instead enrolled in 1580 at the University of Pisa for a medical degree. He was influenced by the lectures of Girolamo Borro, Domingo de Soto and Francesco Buonamici of Florence. Up to this point, Galileo had deliberately been kept away from mathematics, since a physician earned a higher income than a mathematician. However, after accidentally attending a lecture on geometry, he talked his reluctant father into letting him study mathematics and natural philosophy instead of medicine.

Early Scientific Pursuits

While studying medicine in 1581, Galileo observed a swinging chandelier in Pisa's cathedral. He noticed that the chandelier took the same amount of time to swing back and forth, no matter how far it was swinging. When he returned home, he set up two pendulums of equal length and swung one with a large sweep and the other with a small sweep and found that they kept time together. It was not until the work of Christiaan Huygens, almost one hundred years later, that the tautochrone nature of a swinging pendulum was used to create an accurate timepiece.

He created a thermoscope, a forerunner of the thermometer, and, in 1586, published a small book on the design of a hydrostatic balance he had invented, which first brought him to the attention of the scholarly world. Galileo also studied disegno, a term encompassing fine art, and, in 1588, obtained the position of instructor in the Accademia delle Arti del Disegno in Florence, teaching perspective and chiaroscuro. In the same year, upon invitation by the Florentine Academy, he presented two lectures, On the Shape, Location, and Size of Dante's Inferno, in an attempt to propose a rigorous cosmological model of Dante's Inferno. Being inspired by the artistic tradition of the city and the works of the Renaissance artists, Galileo acquired an aesthetic mentality.

Academic Appointments

In 1589, Galileo was appointed to the chair of mathematics in Pisa. In 1591, his father died, and he was entrusted with the care of his younger brother Michelagnolo. In 1592, he moved to the University of Padua where he taught geometry, mechanics, and astronomy until 1610.

Discoveries and Inventions

During his time at the University of Padua, Galileo made significant discoveries in both pure fundamental science as well as practical applied science. He improved upon existing technology, creating an improved telescope. Galileo also studied disegno, a term encompassing fine art, and, in 1588, obtained the position of instructor in the Accademia delle Arti del Disegno in Florence, teaching perspective and chiaroscuro.

The Telescope and Astronomical Observations

Perhaps based only on descriptions of the first practical telescope which Hans Lippershey tried to patent in the Netherlands in 1608, Galileo, in the following year, made a telescope with about 3× magnification. He later made improved versions with up to about 30× magnification. With a Galilean telescope, the observer could see magnified, upright images on the Earth-it was what is commonly known as a terrestrial telescope or a spyglass. He could also use it to observe the sky; for a time he was one of those who could construct telescopes good enough for that purpose.

On 25 August 1609, he demonstrated one of his early telescopes, with a magnification of about 8× or 9×, to Venetian lawmakers. His telescopes were also a profitable sideline for Galileo, who sold them to merchants who found them useful both at sea and as items of trade.

Galileo's observations revolutionized astronomy and provided evidence for the Copernican heliocentric model.

Lunar Observations

On 30 November 1609, Galileo aimed his telescope at the Moon. While not being the first person to observe the Moon through a telescope (English mathematician Thomas Harriot had done so four months before but only saw a "strange spottednesse"), Galileo was the first to deduce the cause of the uneven waning as light occlusion from lunar mountains and craters. In his study, he also made topographical charts, estimating the heights of the mountains. The Moon was not what was long thought to have been a translucent and perfect sphere, as Aristotle claimed, and hardly the first "planet", an "eternal pearl to magnificently ascend into the heavenly empyrian", as put forth by Dante. Comparing patterns of light and shadow in the vicinity of the terminator (the dividing line between light and shadow) at first and third quarter, Galileo could argue convincingly that there exists mountains and valleys on the lunar surface.

Discovery of Jupiter's Moons

On 7 January 1610, Galileo observed with his telescope what he described at the time as "three fixed stars, totally invisible[d] by their smallness", all close to Jupiter, and lying on a straight line through it. Observations on subsequent nights showed that the positions of these "stars" relative to Jupiter were changing in a way that would have been inexplicable if they had really been fixed stars. On 10 January, Galileo noted that one of them had disappeared, an observation which he attributed to its being hidden behind Jupiter. Within a few days, he concluded that they were orbiting Jupiter: he had discovered three of Jupiter's four largest moons. He discovered the fourth on 13 January. Galileo named the group of four the Medicean stars, in honour of his future patron, Cosimo II de' Medici, Grand Duke of Tuscany, and Cosimo's three brothers. Later astronomers, however, renamed them Galilean satellites in honour of their discoverer. Galileo's observations of the satellites of Jupiter caused controversy in astronomy: a planet with smaller planets orbiting it did not conform to the principles of Aristotelian cosmology, which held that all heavenly bodies should circle the Earth, and many astronomers and philosophers initially refused to believe that Galileo could have discovered such a thing.

Phases of Venus

From September 1610, Galileo observed that Venus exhibits a full set of phases similar to that of the Moon. The heliocentric model of the Solar System developed by Nicolaus Copernicus predicted that all phases would be visible since the orbit of Venus around the Sun would cause its illuminated hemisphere to face the Earth when it was on the opposite side of the Sun and to face away from the Earth when it was on the Earth-side of the Sun. In Ptolemy's geocentric model, it was impossible for any of the planets' orbits to intersect the spherical shell carrying the Sun. Traditionally, the orbit of Venus was placed entirely on the near side of the Sun, where it could exhibit only crescent and new phases. It was also possible to place it entirely on the far side of the Sun, where it could exhibit only gibbous and full phases. After Galileo's telescopic observations of the crescent, gibbous and full phases of Venus, the Ptolemaic model became untenable.

Observations of Saturn and Neptune

In 1610, Galileo also observed the planet Saturn, and at first mistook its rings for planets, thinking it was a three-bodied system. When he observed the planet later, Saturn's rings were directly oriented to Earth, causing him to think that two of the bodies had disappeared. Galileo observed the planet Neptune in 1612. It appears in his notebooks as one of many unremarkable dim stars.

Sunspots

Galileo made naked-eye and telescopic studies of sunspots. Their existence raised another difficulty with the unchanging perfection of the heavens as posited in orthodox Aristotelian celestial physics. An apparent annual variation in their trajectories, observed by Francesco Sizzi and others in 1612-1613, also provided a powerful argument against both the Ptolemaic system and the geoheliocentric system of Tycho Brahe. A dispute over claimed priority in the discovery of sunspots, and in their interpretation, led Galileo to a long and bitter feud with the Jesuit Christoph Scheiner. In the middle was Mark Welser, to whom Scheiner had announced his discovery, and who asked Galileo for his opinion. In his Letters, and unlike Scheiner, Galileo correctly identifies sunspots as markings on the solar surface, as opposed to small planets inside the orbit of Mercury. By studying the position of sunspots on successive days Galileo also inferred that the Sun rotates, and established its rotation period as close to one lunar month.

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The Milky Way

Galileo observed the Milky Way, previously believed to be nebulous, and found it to be a multitude of stars packed so densely that they appeared from Earth to be clouds. He located many other stars too distant to be visible to the naked eye.

Other Scientific Contributions

Galileo's contributions extended beyond astronomy to include significant advancements in physics and engineering.

Mechanics and Motion

Galileo's research while at Pisa and Padua was mostly concerned with the problem of motion, in particular motion on inclined planes, of the pendulum, and of freely falling bodies. Galileo's formulation of (circular) inertia, the law of falling bodies, and parabolic trajectories marked the beginning of a fundamental change in the study of motion.

Thermoscope and Hydrostatic Balance

He created a thermoscope, a forerunner of the thermometer, and, in 1586, published a small book on the design of a hydrostatic balance he had invented.

The Galileo Affair

Galileo's championing of Copernican heliocentrism was met with opposition from within the Catholic Church and from some astronomers. In the early 17th century, as a result of his discovery, the great majority of astronomers converted to one of the various geo-heliocentric planetary models, such as the Tychonic, Capellan and Extended Capellan models, each either with or without a daily rotating Earth. By 1616, Galileo’s support for the heliocentric theory had drawn the ire of the Roman Catholic Church. The Inquisition had burned astronomer Giordano Bruno at the stake in 1600 for similar heresies.

Galileo later defended his views in Dialogue Concerning the Two Chief World Systems (1632), which appeared to attack and ridicule Pope Urban VIII, thus alienating both the Pope and the Jesuits, who had both strongly supported Galileo until this point. On June 22, 1633 Galileo was forced to kneel in front of the "Roman Inquisition" and recant his beliefs in the Copernican doctrine and the motion of the Earth. He was tried by the Inquisition, found "vehemently suspect of heresy", and forced to recant. Galileo was soon summoned to Rome, accused of willfully disobeying the Papal order against the propagation of Copernicus’ theory. In 1633, the Inquisition found Galileo guilty of the charge, and forced him to publicly withdraw his belief in the heliocentric theory, and sentenced him to life imprisonment. Due to his advanced age, he was permitted to serve his term under house arrest at his villa outside Florence.

He was prohibited from publishing, was sentenced first to prison and then to house arrest, and was forced to “abandon the false opinion that the Sun was the centre of the universe and immovable, and that the Earth was not the centre of the same and that it moved.” Despite this, in 1638 he published Discourses and Mathematical Demonstrations Relating to Two New Sciences beyond the Inquisition’s jurisdiction in Holland.

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