| |
| | World Almanac for Kids |
 | | The Ptolemaic theory held that Earth is stationary and at the center of the universe; closest to Earth is the Moon, and beyond it, extending outward, are Mercury, Venus, and the Sun in a straight line, followed successively by Mars, Jupiter, Saturn, and the so-called fixed stars. |
 | | To explain the various observed motions of the planets, the Ptolemaic system described them as having small circular orbits called epicycles; the centers of the epicycles, on circular orbits around Earth, were called deferents. |
 | | These efforts failed, however, to resolve the many inconsistencies in the Ptolemaic system, which was finally superseded in the 16th century by the Copernican system. |
| www.worldalmanacforkids.com /explore/space/ptolemicsystem.html (202 words) |
|