Belief that Earth is at the center of the universe. The geocentric theory of the universe dominated European astronomical thinking for more than two millennia. The original geocentric theory that Earth is stationary and that the entire universe revolves around it is sometimes attributed to the Pythagoreans, an ancient community established in Croton in Southern Italy by Pythagoras in the sixth century B.C.E. But the idea is probably much older, perhaps dating back to ancient Egyptian or Babylonian times. Pythagoras believed that the entire universe could be described in terms of numbers and used his famous theorem about the relationship of the sides of a right-angled triangle to combine numbers and geometry. His work formed the basis for trigonometry and allowed later philosophers to chart the positions of stars.
Although some ancient thinkers challenged the geo¬ centric view of the universe philosopher Aristarchus of Samos, for instance, proposed a heliocentric (Sun-centered) model in the third century B.C.E. most accepted the view of Earth as the center of the universe. Most influential among Pythagoras’s followers were the fourth- century B.C.E. philosopher Aristotle, the second-century B. C.E. astronomer Hipparchus, and the second-century C. E. astronomer Ptolemy. Aristotle was a polymath who studied and wrote about topics ranging from biology to literature. He was also the tutor of Alexander the Great of Macedon. Because his views were so widely spread through Alexander’s conquests, Aristotle was accepted as the voice of authority by most of the European and Mideastern world.