Astronomy at first simply an astrological pursuit where objects and motions of object in the sky were explained using archaic understandings of the universe, however this was all before Galileo turned his telescope to the universe. He applied scientific methods, mathematical laws and simple logical thinking to the objects he observed. Modern science of observational astronomy is based on Galileo’s methods.
Telescopes are used to help us understand our universe, Galileo although thought of as the inventor of the telescope was in fact not however, he did teach us and created a new science by turning the telescope to the night universe.
1609 was the first time when he learned of the telescope he then went on to make a copy for himself. The first telescope magnifies images up to three times. Over a decade as he continued his work of making telescopes his creations took him to his most powerful of telescopes, it was able to magnify objects up to ten times. Obviously it allowed him to see things that he had never been able to before, consequently this changed our view of the universe and of the object sin the sky.
The moon was the first interest of Galileo observing it carefully with his telescopes he made an important discovery. Depending on where the moon was in relation to the sun he discovered that the dark areas of the moon grew and shrunk. He correctly discovered that in fact these dark areas where shadows from craters and mountains. He further explained with geometry that the height of the mountains and depth of the craters could be correctly calculated. This was an astonishingly important revelation in our view of the universe because it was previously believed that the moon was a smooth surfaced object.
Four largest moons around Jupiter was the next most important of Galileo's discoveries. He could see what the naked eye could not with his ten timed magnified telescope. He learned from observation that they moved too. He also proved with calculation and further observation that they literally revolved around Jupiter. It was previously believed that everything revolved around the Earth so you see this really was another important discovery as again it inflicted changing views of the universe.
As he carried on his ever so important observations he soon discovered spots on the sun and the rings of Saturn. His observations in the sky spurred on many other telescope makers and astronomers to further explore the amazing and mysterious objects in the sky. But more importantly he also spurred on other astronomers to apply the laws and lessons of mathematics and logic to their observations in a quest to understand how the universe works.
1610 was when the modern science of telescope was clearly born in this time Galileo published his work and called it 'Sidereus Nuncius' or the 'Starry Messenger' Considered to be the most important written scientific works his findings are still accessible till this very day.