Galileo Galilei is widely considered to be the "father" of modern science, and, hence, of the world we know today. He was the first experimental physicist in the modern sense, and his work was the foundation on which Isaac Newton would, in the following generation, build the science of mechanics. However, Galileo achieved his greatest fame (and notoriety) for a series of sensational discoveries with the newly invented telescope. These discoveries include craters on the moon, spots on the sun, the phases of Venus, stars invisible to the naked eye and the moons of Jupiter. More than any one man, Galileo was responsible for the replacement of Ptolemy's geocentric (Earth centered) universe with the heliocentric (Sun centered) universe of Copernicus.

Galileo was born in 1564 in Pisa, Tuscany. His early schooling was in nearby Florence, but he returned to Pisa to attend the university there. He later became a professor of mathematics at that same institution and began the study of bodies in motion. His studies led him to conclude that physics of Aristotle, then still accepted as authoritative throughout Europe, was seriously flawed. Legend has it that he disproved Aristotle's assertion that heavy bodies fall faster than light bodies by dropping two unequal weights off the leaning tower of Pisa.

Galileo was an ambitious man, so, much like scholars today, he sought to enhance his position by seeking employment at a more prestigious university. This led him to Padua, then under the control of Venice, and home of the second oldest institution of higher learning in Italy. The University of Padua (nicknamed Ill Bo, "the Ox", from a nearby tavern) could boast of several illustrious alumni, in particular the poet Dante, who's Devine Comedy summarized the medieval view of the world (Earth in the center, hell below and heaven above) and the astronomer Copernicus, who had sent the Earth spinning around the Sun some 50 years before Galileo's time . Galileo became a professor at the university in 1592 and remained there until 1610. His stay at Padua was momentous, because it was here that he became convinced that Copernicus was right about the Earth moving around the Sun and set out to find evidence to support this view. He was helped tremendously in this project when he heard about the invention in Holland of a device which made distant objects appear nearer. We, of course, call this device a telescope, and Galileo immediately set out to make one for himself. Galileo did not just duplicate the telescopes that were then available in northern Europe, he improved their performance. His best early telescope had a magnifying power of about 30 times, and with this he was able to make his celebrated discoveries of craters on the moon, the phases of Venus, Sunspots, and, perhaps the greatest of all, the moons of Jupiter.

On weekends Galileo went down to Venice to relax with friends, especially Gianfrancesco Sagredo, a wealthy nobleman who had a palace (Palazzo Sagredo) on the Grand Canal and who shared Galileo's scientific enthusiasms. It was here that he met a woman named Marina Gamba with whom he established a long term relationship. This liaison eventually resulted in three children. (Galileo was particularly close to his eldest daughter and maintained a life long literary correspondence with her, some of which survives to this day.) Sagredo was well connected to the rulers of the Venetian state, and having friends in high places gave Galileo an opportunity to impress people who were in a position to further his career. He demonstrated his telescope from the top of the Campanile (bell tower) in Piazza San Marco and showed how it could be used as an early warning system to determine whether a distant approaching ship was "friend or foe". The Venetian power brokers liked what they saw and offered Galileo permanent employment in Venice.

This was all well and good, but Galileo's real ambition was to return to Florence as a full professor of philosophy, both because of Florence's preeminence in Renaissance culture (hence, carrying more prestige) and because it was in his native Tuscany , near his daughter who was by that time a nun in the convent of San Matteo. Today Venice and Tuscany are part of a united Italy, but then they were separate states. During this period Tuscany was ruled by the powerful Medici family who had final say on all professional appointments in their territory. Galileo's strategy to get back to Florence involved using the offer from Venice to pad his resume and buttering up the Medici by naming the newly discovered moons of Jupiter in their honor. Thus the moons of Jupiter were christened the Medician Stars. Conveniently, there were four powerful Medici brothers to match the four moons, but no one outside of Tuscany ever thought much of these names, and they were quickly discarded in the rest of Europe in favor of the classical Io, Ganeymede, Europa, and Collisto. However, it was a good move for Galileo, as he was welcomed to Florence with open arms, honors and a permanent position as mathematician and philosopher to the Medici court.

Galileo set up housekeeping in the Villa dell'Ombrellino, a mansion in the fashionable Bellosguardo district of Florence. Here he continued his studies on motion and his astronomical observations. This was perhaps the most productive period of his life and he wrote a number of books announcing new discoveries and stating his clear belief in the truth of the heliocentric system proposed by Copernicus. This view was not well received by either the academic or religious establishments and concerted attacks Galileo and his beliefs were launched from all directions. The first public challenge was delivered in a sermon by father by Father Tommaso Caccini on December 21, 1614 at the church of Santa Maria Novella. Father Caccini began with a reading from the New Testament "Ye men of Galilee why stand ye gazing into the heavens?" , and then proceeded to denounce the heliocentric system and all those who supported it. From then on, for the next 17 years, Galileo was on the defensive, playing a "cat and mouse" game with the authorities, sometimes seeming to pretend that he really thought of the heliocentric system only as an interesting mathematical hypothesis, while at other times strongly implying that Copernicus' model was the only true way to view the world.

Galileo's problems with the Catholic Church is a complicated subject. Briefly, he was forbidden by the Pope to publish anything stating that Copernicus' system was a proven fact. However, he was still allowed to discuss the heliocentric idea in print as long as it was clearly stated that the system was no more than an unproven hypothesis. In 1632, while still at the Villa dell'Ombrellino he wrote Dialogue on the Two Chief World Systems, a book that he hoped would satisfy the demands of ecclesiastical establishment while at the same time presenting rigorous arguments in favor of Copernicus. Instead, the book proved to be his undoing. Although Galileo maintained that his Dialogue was an even handed presentation of both geocentric and heliocentric systems, it was clear that the sympathies of the author was overwhelmingly with the new heliocentric view of the world. The church authorities felt that Galileo had violated the Pope's injunction and, therefore, had to be punished. Galileo was summoned to Rome, put on trial in the monastery attached to Santa Maria sopra Minerva basilica, and found guilty. He was sentenced to live under house arrest for the rest of his life and was forbidden to teach, write or otherwise discuss the Copernican system or any other matter pertaining to cosmology.

Galileo spent the last ten years of his life at the villa il Giorello in Arcetri, a suburb of Florence in the hills overlooking the city. As this house was a only a short distance from his daughter's convent, one small modification to his terms of confinement was that he was allowed take the short walk to San Matteo to visit her. Galileo visited her often until her death in April of 1634. Although he was not allowed to discuss cosmology, in his final years he was able to publish what many consider his most important scientific work, Discourse on Two New Sciences, which laid the foundation for the science of mechanics.

Galileo died on January 8, 1642 and was buried in Franciscan church of Santa Croce in Florence. His original tomb was in a small room in the Novices' Chapel , but in 1737 after the cosmological controversy of the previous century had faded, Galileo's admirers were able to persuade the authorities to allow his body to be relocated into the main basilica in a place of honor. Here they erected an elaborate mausoleum facing that of another of Florence's famous sons, Michelangelo. Despite this concession, Galileo's official rehabilitation by the church took much longer. The Dialogue remained on the index of forbidden books until 1835 and it was not until 1992 that Pope John Paul II fully exonerated him, acknowledging "mistakes were made" by the ecclesiastical authorities in handling the issue back in 1633.

References:

Galileo, A Life by James Reston Jr. Harper Collins 1994

Galileo's Daughter by Dava Sobel Penguin Books, 1999

Galileo's Italy