GALILEO

Galileo is the first to have pointed to the sky a new optical instrument, the telescope through which he discovered a hitherto unsuspected multitude of things: sunspots, craters on the Moon, satellites of Jupiter, crescent of Venus, Saturn's ring, which he took for two huge satellites on either side of the planet, and a multitude of stars invisible to the naked eye in the Milky Way. 

His observations confirmed the Copernican theory.