In the 5th century BCE, the Greek philosophers Philolaus and Hicetas speculated separately that the Earth was a sphere revolving daily around some mystical "central fire" that regulated the universe. Anaxagoras proposed that the Sun is a star around 450 BCE. In the 3rd century BCE, Aristarchus of Samos extended this idea by proposing that the Earth and other planets moved around a definite central object, which he believed to be the Sun though this was not widely accepted until the 17th century and not proven until the 19th.