Among the Arabs and Persians were great calculators and mathematicians who worked to improve the cosmological explanation of astronomical measurements. For example, Nasir al-din al-Tusi at Maragha produced a particularly innovative addition to Ptolemy's circular motions. The "Tusi couple" calculates a linear motion from a combination of uniform circular motions. In his revolutionary work on the solar system published in 1543, Copernicus used a strikingly similar device. Also, Copernicus used a model for the Moon's motion identical to one devised two centuries earlier by the astronomer Ibn al-Shatir in Damascus. Copernicus cited the works of Islamic astronomers and certainly learned from them. Historians are still trying to determine the full extent of his intellectual debt.
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