ABSTRACT

Eudoxus of Cnidus led an immensely active life, and had many interests. He developed theories in philosophy, theology, astronomy, geography and mathematics and was also active on developing a code of laws for his own city. Eudoxus performed a most remarkable feat of mathematics and astronomy, and effectively established a research programme for astronomy that was to last around 2,000 years. The modern explanation of retrograde motion is that the earth and the planets each have different sizes of orbits and different speeds of orbits. Plato supposed all of the fixed stars to be on one sphere, which rotated once in 24 hours. The outer sphere carries the fixed stars, as with Plato’s model. So concentric sphere astronomy gave way to another type of astronomy, known as epicyclic astronomy, developed by the later astronomers, Apollonius and Hipparchus, and brought into a completed system by Ptolemy in the second century AD, who was perhaps the greatest astronomer in the ancient world.