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Section 1: The Ancient Universe
Ancient philosophers set the stage for the role that the stars would play until the seventeenth century. Plato's Timaeus established the sphere of the stars and its circular movement. He described the sphere's dominion over the motion of the planets and sketched in broad strokes the size, speed, and direction of their orbits within it.
 
Aristotle provided the physical foundations for the motions of the planets, defining the number of spheres required to account for their observed motions. He established the necessity of the role of the fixed stars in moving the planets in their orbits.

Epicycles were fully integrated into this earth-centered system by Ptolemy in part to account for retrograde motion. He refined the model into an effective and accurate tool for predicting the motions of the planets.

A depiction of the Ptolemaic system with portraits of Ptolemy and the author below. Johannes Regiomontanus In Almagestu[m] Ptolomei, 1496.
Regiomontanus
Ptolemy
Plato.
Aristotle

Above left to right:
* Historiated initial showing one astronomer making observations and another recording them. Almagestu[m], Ptolemy, 1515.
* Plato. Timaeus, 1520. The publisher Badius uses a press as his printer's device.
* Opening page of De Caelo, Aristotle, Opera Graeca, 1495.

Linda Hall Library of Science, Engineering & Technology
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This exhibition is made possible by generous support from Mr. & Mrs. James B. Hebenstreit and Mrs. Lathrop M. Gates.