Galileo was an Italian physicist and astronomer who with the German astronomer Johannes kelper initiated the scientific revolution that began the work of Sir Isaac Newton. Galileos main interest was astronomy he used the telescope which he invented using optic lenses to see sunspots on the sun loonier mountains and valleys the four largest satellites of Jupiter and the phases of Venus. He also discovered the laws of falling objects and the motion of moving projectiles.
At Padua Galileo invented a calculating compass for the practical solution of mathematical problems. He used his studies of physics and measurement to discover the law of falling objects and the way projectiles move. He also studied pendulums he was sitting in a room one day and was watching a pendulum swing back and forth and he found that the timing of the swings was the same each time this theory that he discovered is now used in a very popular invention called the clock. At this point in time he showed very little interest in astronomy although he developed the theory that the earth revolves around the sun. In 1609 Galileo heard of the first spy glass that was invented in Holland. So Galileo presented a telescope with about the same power of a modern field glass.
By December of 1609 Galileo had built a telescope of 20 times the magnification with which he discovered mountains and craters on the moon. He also saw that the Milky Way was made up of stars and he discovers the four largest satellites of Jupiter. He published these findings in March 1610 in the starry Messenger.
The more that Galileo observed our universe through his telescope the more he realized he finally came to the conclusion that the sun was not the center of the universe the earth was and because he went against the Rome catholic church in saying this he was sentenced to life in prison.