Galileo Galilei

 Galileo Galilei (1564-1642) made major contributions to the fields of physics, astronomy, cosmology, mathematics and philosophy. He invented an improved telescope that let him observe and describe the moons of Jupiter, the rings of Saturn, the phases of Venus, sunspots and the rugged lunar surface. His flair for self-promotion earned him powerful friends among Italy’s ruling elite and enemies among the Catholic Church’s leaders. His advocacy of a heliocentric universe brought him before religious authorities in 1616 and again in 1633, when he was forced to recant and placed under house arrest for the rest of his life. Galileo was born in Pisa, Tuscany, on February 15, 1564, the oldest son of Vincenzo Galilei, a musician who made important contributions to the theory and practice of music and who may have performed some experiments with Galileo in 1588–89 on the relationship between pitch and the tension of strings. The family moved to Florence in the early 1570s, where the Galilei family had lived for generations. 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. During this period he designed a new form of hydrostatic balance for weighing small quantities and wrote a short treatise, La bilancetta (“The Little Balance”), that circulated in manuscript form. He also began his studies on motion, which he pursued steadily for the next two decades.