Galileo studied Copernicus’s theory about how the sun and other planets circulate around us. So then Galileo wanted to see for himself, he made his improved telescope and took a look at jupiter, then made a discovery of four planets that are circling around it. Galileo wrote many books as well and published them, most of them were about his theories and inventions.
Galileo had made many discoveries and many inventions. He made mostly inventions because, after being banned from teaching his theories to kids/other people, he was then sentenced house imprisoned permanently from trying to teach kids something he believes is true and right! Galileo invented the new and improved telescope, the use of artillery, clocks and meteorology.