Before the telescope was invented people used a variety of naked eye instruments. People also used astronomy to predict when things would happen such as religious dates, solstices, equinoxes, and to tell time. Astrolabes and sextants were used by seamen as a navigation tool for as long as people had traveled the seas. They were replaced in the 20th century by GPS’s.
Ancient astronomers like Aristotle could make observations and inferences based on what they saw, but often their conclusions weren't right or their predictions were inaccurate. After the telescope was invented, people could make more accurate observations about the stars and planets. The telescope let people see objects farther away and helped add reasons to believe in the Copernican system. The people that used the telescope were able to point out errors in the Ptolemaic system. In the Ptolemaic system, all heavenly bodies revolved alone around the Earth and were perfect, crystalline spheres. Galileo also revolutionized how scientists created new theories. He was one of the first to test his theories in experiments. His most famous experiment was when he dropped two different sized balls off the Leaning Tower of Pisa to prove two Jesuit scientists wrong. They said that the balls would fall at the same speed but had never actually done and experiment to prove it. Galileo made scientists realize that some of their beliefs had never been proven by actual data and when they did the experiment the result was often very different that what they though would happen.