Aristarchus of Samos determined the Sun was about six to seven times larger than the Earth which led him to the idea of that the Earth actually revolves around the Sun.
Claudius Ptolemy believed the Earth was the center of the universe.
Copernicus published 'On the Revolutions', just before his death. In it, he proposed that the center of the universe was not the Earth, but the sun. He suggested that the Earth's rotation accounted for the rise and setting of the sun.
Galileo's observations of the phases of Venus proved Copernicus's heliocentric theory. The telescope he made could magnify objects up to twenty times.
Johannes Kepler created the first three laws of planetary motion.
Bessel was the first astronomer to publish the distance between stars and planets.