Ibn al-Shatir
Damascene astronomer whose lunar and planetary models were mathematically identical to Copernicus' later formulations.
Who or what
Ala al-Din Abu'l-Hasan Ali ibn Ibrahim ibn al-Shatir (1304–1375) was an Arab astronomer and muwaqqit (timekeeper) at the Umayyad Mosque in Damascus.
He produced new planetary models that eliminated the equant and epicycle anomalies in Ptolemaic astronomy, using only combinations of uniformly rotating circles.
Why it mattered
Ibn al-Shatir's models for the Moon and Mercury are mathematically identical to those later used by Copernicus, raising profound questions about transmission of ideas.
He was a practicing timekeeper who needed accurate astronomical tables for determining prayer times.
Key works and moments
His lunar model correctly predicted the Moon's distance variation, which Ptolemy's model could not.
His planetary models provided more accurate predictions of planetary positions than Ptolemy's Almagest.
Further detail
He used a system of epicycles and deferents that exactly matches Copernicus' later arrangement for the Moon: two epicycles on a deferent centered on Earth.
For Mercury, his model is virtually identical to Copernicus' model for that planet.
Legacy
His work provides the strongest evidence that Copernicus' heliocentric models had precursors in Islamic astronomy.
Shows the continuity of astronomical science across cultures and centuries.
More in Islamic Golden Age
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