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Ptolemy's Theory of the Inferior Planets

Ptolemy's Theory of the Inferior Planets JHA, xx (1989) N. M. SWERDLOW, The University of Chicago At its foundation, Ptolemy's astronomy is empirical. Much of the Almagest is devoted to the derivation of numerical parameters from observations selected to isolate particular quantities so that they may be found in the most direct way. But in addition the hypotheses, models, of the Sun, Moon and planets were also derived or confirmed by observation although Ptolemy gives only brief descrip­ tions of his procedures without citation of specific observations. In this way, for example, in 9.5 he justifies the use of an epicycle with motion in the positive sense, of increasing longitude, at apogee for the second inequality of the planets, and an eccentric for the first inequality, and in 10.6 he briefly describes his demonstration that the eccentricity must be bisected, separating the centre of uniform motion of the centre of the epicycle from the centre of constant distance. The brevity of the accounts of these demonstrations has been of serious consequence for the history of astronomy because Ptolemy's description of the motions of the bodies in the heavens and his justification of the hypotheses to account for them - both correct, at least in principle, http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal for the History of Astronomy SAGE

Ptolemy's Theory of the Inferior Planets

Journal for the History of Astronomy , Volume 20 (1): 32 – Feb 1, 1989

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References (13)

Publisher
SAGE
Copyright
© 1989 SAGE Publications
ISSN
0021-8286
eISSN
1753-8556
DOI
10.1177/002182868902000104
Publisher site
See Article on Publisher Site

Abstract

JHA, xx (1989) N. M. SWERDLOW, The University of Chicago At its foundation, Ptolemy's astronomy is empirical. Much of the Almagest is devoted to the derivation of numerical parameters from observations selected to isolate particular quantities so that they may be found in the most direct way. But in addition the hypotheses, models, of the Sun, Moon and planets were also derived or confirmed by observation although Ptolemy gives only brief descrip­ tions of his procedures without citation of specific observations. In this way, for example, in 9.5 he justifies the use of an epicycle with motion in the positive sense, of increasing longitude, at apogee for the second inequality of the planets, and an eccentric for the first inequality, and in 10.6 he briefly describes his demonstration that the eccentricity must be bisected, separating the centre of uniform motion of the centre of the epicycle from the centre of constant distance. The brevity of the accounts of these demonstrations has been of serious consequence for the history of astronomy because Ptolemy's description of the motions of the bodies in the heavens and his justification of the hypotheses to account for them - both correct, at least in principle,

Journal

Journal for the History of AstronomySAGE

Published: Feb 1, 1989

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