Aristarchus of Samos
Aristarchus of Samos was an ancient Greek astronomer and mathematician who presented the first known heliocentric model that placed the Sun at the center of the known universe, with the Earth revolving around the Sun once a year and rotating about its axis once a day. He was a student of Strato of Lampsacus, who was the third head of the Peripatetic School in Greece. According to Ptolemy, during his time there, he observed the summer solstice of 280 B.C.. Along with his contributions to the heliocentric model, as reported by Vitruvius, he created two separate sundials; one that is a flat disc and one that is hemispherical. He was influenced by the concept presented by Philolaus of Croton of a fire at the center of the universe, but Aristarchus identified the "central fire" with the Sun and he put the other planets in their correct order of distance around the Sun.