Anaximander was a pre- Socratic Greek philosopher who is widely referred to as the "father of astronomy" and even as the "father of cosmology" as a result of his works to explain the origin and makeup of the physical universe. He is regarded as the most important of the Ionian philosophers, and was a pupil of Thales. Traditionally, details of his life and opinions are perpetuated not only by Aristotle and Theophrastos, but also by a great number of secondary authors. He lived throughout the fifth and fourth centuries, BCE, and was most likely the first philosopher to try to rationalize the system of the Earth, Sun, and Moon by the use of geometry and mathematics. Anaximander was also said to have created the first map of the world, however, like much of the rest of his works, this has been lost since his time. There is, however, documentation of Anaximander being responsible for the conception of the first mechanical model of the world, which is outlined by a geocentric model. He postulated that the Earth was at the center of the universe, and that its shape was convex and cylindrical, with life existing on one of the two flat sides. Beyond the Earth, sits the other planets, which Anaximander also details the order of. Next are the fixed stars, which he regarded as wheel-like condensations of air filled with fire, provided at certain places with openings through which flames are discharged. Anaximander places the Moon beyond these stars, and assumed it to also be wheel-like in shape, being nineteen times the size of Earth. Finally, on the top of the universe is the Sun, which interacts with the Moon, and the relationship between them is described in terms of aperture, in which a stoppage in would lead to eclipses.