Galileo Galilei (1564-1642) was an Italian philosopher, mathematician, physicists, and astronomer. Galileo began studying at the University of Pisa in 1581, where he initially was to study medicine, but later decided to study Aristotelian mathematics and philosophy. He would later begin to experiment on his own to challenge Aristotle using his principle of inertia. One of his experiments involving objects rolling down ramps allowed him to show that all objects fall at a constant acceleration, regardless of their weight, which contradicted the common belief at the time that heavier objects fell faster.
Galileo’s most important discoveries came after he made his first telescope in 1609, which he modeled after other telescopes created in other parts of Europe. His telescopes were able to magnify objects far better than those of his contemporaries. With his telescope, he discovered that the moon was not smooth as most people had assumed, but had craters and mountains, and by measuring the shadows of these mountains he was able to determine the height of the Moon’s mountains. He also discovered four of Jupiter's moons, which disproved the belief that only the earth had a moon. Galileo published his first scientific book, The Starry Messenger, in 1610 based on his findings. His discoveries supported Copernicus’ theory that the earth revolved around the sun. Although his works brought him fame, his support for the heliocentric model drew harsh criticisms from the Catholic Church. At the time, several of Copernicus books were banned by the Catholic Church because of conflicts with the Bible and Church doctrine. Galileo continued to defend Copernicus, leading him to publish his controversial work, Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican. Shortly after publication, this book was banned by the Catholic Church, and Galileo was called to Roman Inquisition to stand trial for heresy, where he had to promise to no longer defend Copernicus’ theory. Galileo was later called to Roman Inquisition two more times, and was finally convicted of heresy. He was placed on house arrest for the remainder of his life and was not allowed to publish any more works. While under house arrest, he managed to publish his final work, Discourses and Mathematical Demonstrations Relating to Two New Sciences, which encompassed his work on motion.