Nur ad-Din al-Betrugi (also spelled Nur al-Din Ibn Ishaq Al-Bitruji and Abu Ishâk ibn al-Bitrogi; another spelling is al Bidrudschi) (known in the West by the Latinized name of Alpetragius) (died ca. 1204 AD) was an Arab astronomer and philosopher of the Islamic Golden Age (Middle Ages). Born in Morocco, he settled in Seville, in Andalusia. He became a disciple of Ibn Tufail (Abubacer) and was a contemporary of Averroës.
Al Betrugi wrote the Kitab-al-Hay’ah, translated from the Arabic into Hebrew, and then into Latin by Michael Scot as De motibus celorum (first printed in Vienna in 1531).
He advanced a theory on planetary motion in which he wished to avoid both epicycles and eccentrics, and to account for the phenomena peculiar to the wandering stars, by compounding rotations of homocentric spheres. This was a modification of the system of planetary motion proposed by his predecessors, Ibn Bajjah (Avempace) and Ibn Tufail (Abubacer).
The crater Alpetragius on the Moon is named after him.