Galileo's main impact on the world was his improvement upon the telescope and being the first to use it in the science of astronomy. He also supported the Copernican system that stated that planets orbit the sun rather than the Earth as the Catholic Church said at the time. His other contribution was to contradict Aristotle's teachings that heavier objects fall faster than lighter ones.
Galileo Galilei was an Italian astronomer who challenged many of the commonly held ideas of his time. His discoveries of the laws of motion and telescope improvements are still considered the foundations of many scientific beliefs today. Galileo worked extensively with weights to counter and disprove Aristotle's theory about weight. He found that all weights fell at the same speed regardless of their mass.
It is sometimes thought that Galileo actually invented the telescope, but the truth is that he took an invention already in place and improved it. Further, he began using it in the study of astronomy, which was new at the time. His improvements enabled him to magnify things eight to nine times versus three. This is how he confirmed the theory of Copernicus that stated that Earth revolved around the sun.