ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY
Wheel chart for Jupiter's orbit. This volvelle (wheel chart) is from the astronomical atlas Astronomicum Caesareum (1540) by the German printer Petrus Apianus (1495-1552). A volvelle involves several layers of paper placed over each other, which are then rotated to produce the desired result. In this case, to show the position of Jupiter in the night sky for a given latitude, time and date. The Latin names of the zodiacal constellations are around the rim of both the main wheel, and the smaller wheel. Jupiter rotates around this smaller wheel (the epicycle) as the epicycle itself rotates around the larger wheel (the deferent). This Ptolemaic system of epicycles was later replaced by the heliocentric Copernican system (1543) and Kepler's ellipses (1609).
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