Ala al-Din Abu'l-Hasan ali ibn Ibrahim ibn al-Shatir

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Ala al-Din Abu'l-Hasan ali ibn Ibrahim ibn al-Shatir

c. 1305-c. 1375

Arab astronomer who sought to restore uniform circular motion to planetary theory by replacing Ptolemy's eccentric deferent and equant with secondary epicycles. This eliminated a major defect of Ptolemaic lunar theory by reducing the variation of the Moon's distance. Though developed within a geocentric framework, Ibn al-Shatir's models are mathematically equivalent to those later developed by Nicolaus Copernicus; however, no direct influence has been established. Ibn al-Shatir also constructed various instruments, including sundials, astrolabes, and quadrants.

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Ala al-Din Abu'l-Hasan ali ibn Ibrahim ibn al-Shatir

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Ala al-Din Abu'l-Hasan ali ibn Ibrahim ibn al-Shatir