Galileo was born in Pisa, Italy in the late 1500's. He first became a math teacher even though he had no degree in the subject, and here he began his path to greatness. A baby step towards Galileo Galilei astronomy was when he demonstrated to students that different weight objects fell at the same speed, counter to Aristotle's teachings. He wasn't invited back to teach, and so moved to a position at the University of Padua. It was there that his ideas about astronomy truly began.In Padua, Galileo invented the compass and began studying physics. He expanded his work on falling bodies, writing formula to describe them as well as the parabolic path of projectiles. These two ideas were key to astronomy as it progressed. However except for an allegiance to the work of Copernicus over Ptolemy and Aristotle, Galileo claimed to be disinterested in astronomy. It was Copernicus who first described a solar system in which planets orbit the sun. Aristotle and Ptolemy held that the solar system was centered around the Earth, and even the sun rotated around our home. As time went by Copernicus, and Galileo, were proven correct.Galileo was the first to look at the night sky through a spyglass, thus using the first telescope. With a magnification of 20, this telescope helped Galileo discover mountains and craters on the moon. He also learned that the milky way was made up of individual stars. Next he found the four largest moons of Jupiter. He published his findings and became the court mathematician in Florence. Now he could devote full time to his studies. It took him only 9 months to discover Saturn's phases. This was another nail in the coffin for Ptolemy's and Aristotle's ideas about the solar system.Galileo's original dispute was with Aristotle's teachings. Many scientists agreed with Galileo, and so published his findings. But Aristotle was popular with the church because an Earth centered solar system put man's home, and thus man, at the center of things. A Florence priest denounced Galileo Galilei astronomy in 1614. Galileo's response was a letter stating that science was above the bible. A cardinal demanded Galileo stop talking about a moving Earth. Galileo complied, continuing his study of falling objects, comets, and methods to determine longitude at sea based on the phases of Jupiter's moons.