Eudoxus (c. 408–c. 353 BC)

Greek mathematician and astronomer. He devised the first system to account for the motions of celestial bodies, believing them to be carried around the Earth on sets of spheres. Work attributed to Eudoxus includes methods to calculate the area of a circle and to derive the volume of a pyramid or a cone.

Probably Eudoxus regarded the celestial spheres as a mathematical device for ease of computation rather than as physically real, but the idea was taken up by Aristotle and became entrenched in astronomical thought until the time of the 16th-century Danish astronomer Tycho Brahe.

Life Eudoxus was born in Cnidus, southwestern Asia Minor. In early life he attended lectures by the philosopher Plato. He was also a philosopher.

Mathematics and astronomy In mathematics, Eudoxus' early success was in the removal of many of the limitations imposed by Pythagoras on the theory of proportion. He also established a test for the equality of two ratios. He devised the hypothesis of concentric spheres to explain the stationary points and retrogradations in the motions of the planets. Eudoxus is said to have been the one who first fixed the length of the year as 365.25 days, and to have invented the sundial

Books The model of planetary motion was published in a book called On Rates. Further astronomical observations were included in two other works, The Mirror and Phaenomena. In a series of geographical books with the overall title of A Tour of the Earth, Eudoxus described the political, historical, and religious customs of the countries of the eastern Mediterranean.