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THE NEW ASTRONOMY OF IBN AL-HAYTHAM

Published online by Cambridge University Press:  01 March 2009

CHRISTIAN HOUZEL
Affiliation:
Archives Bourbaki, CNRS, 7 rue Guy Môquet, B.P. n° 8, 94801 Villejuif Cedex, France Email: houzel@vjf.cnrs.fr

Abstract

In order to get rid of the contradictions he had identified in Ptolemy’s Astronomy, Ibn al-Haytham abandons cosmology and develops a purely kinematic description of the movement of the wandering stars. This description culminates with the proof that such a star, during its daily movement, reaches exactly one time a maximum height above the horizon and that any inferior height is reached exactly twice. The proofs of these facts necessitates new mathematical tools and Ibn al-Haytham is led to establish very sophisticated statements concerning the variation of certain ratios of arcs of circles on the sphere. He also introduces the fruitful idea of assimilating a very small spherical triangle to a plane triangle.

Type
Research Article
Copyright
Copyright © Cambridge University Press 2009

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