What new invention did galileo perfect and what did he use it to prove?

Galileo is considered as one of the bravest and most important scientists that lived in the late Middle Ages. He was very interested in astronomy, how the universe looks, how it works, what is the role of Earth in all of that. Despite being constantly under pressure, and even under threat of being executed, Galileo was not giving up on his dream and interests. He managed to develop a new, revolutionary invention in secrecy, the telescope. He used his invention in order to be able to observe the universe better. Once he was able to see some things in the sky much better, Galileo started to note things, to draw them, to notice patters, the movements of the space objects he was able to see. Eventually he came to a conclusion that the Earth was not the center of the universe and that everything spins around it, but instead, the Sun is the center of the universe (not true, but still big step forward) and that the Earth and the other planets spin around it. The only object that he noticed spinning around Earth was the Moon. This was not well accepted by the clergy, as that would have deteriorated the reputation and trustworthiness of the church in the people's eyes, so they were doing everything they could to stop such thing to come out in public. Eventually though, the church lost the battle, and Galileo's findings reached the public and opened up a door for further explorations.