Since the Earth's rotation is irregular, any time scale derived from it such as Greenwich Mean Time led to recurring problems in predicting the Ephemerides for the positions of the Moon, Sun, planets and their natural satellites.
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The work of Ali Qushji (d. 1474), who worked at Samarqand and then Istanbul, is seen as a late example of innovation in Islamic theoretical astronomy and it is believed he may have possibly had some influence on Nicolaus Copernicus due to similar arguments concerning the Earth's rotation.
After stints in the USA at the Institute for Advanced Study in Princeton and at Caltech, he returned to the Netherlands in 1990 to become Professor of Theoretical Astronomy at Leiden.