Nur ad-Din al-Bitruji

12th-century Iberian Arab astronomer and Qadi

Nūr al-Dīn ibn Isḥaq al-Biṭrūjī, known in the West by the Latinized name of Alpetragius, was an Arab astronomer and qadi in al-Andalus. Al-Biṭrūjī was the first astronomer to present the concentric spheres model as an alternative to the Ptolemaic system, with the planets borne by geocentric spheres. Another original aspect of his system was proposing a physical cause of celestial motions. His alternative system spread through most of Europe during the 13th century.

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