explanation was used up to the seventeenth century by the European Scholastics to account for Galileo's observations of spots on the moon's surface, until the Scholastics such as Antoine Goudin in 1668 conceded that the observation was more likely caused by mountains on the moon. He and Ibn Bajja observed sunspots, which they thought were transits of Venus and Mercury between the Sun and the Earth. In 1153 he conducted astronomical observations in Marrakesh, where he observed the star Canopus (Arabic: Suhayl) which was invisible in the latitude of his native Spain. He used this observation to support Aristotle's argument for the spherical Earth. Averroes was aware that Arabic and Andalusian astronomers of his time focused on "mathematical" astronomy, which enabled accurate predictions through calculations but did not provide a detailed physical explanation of how the universe worked. According to him, "the astronomy of our time offers no truth, but only agrees with the calculations and not with what exists." He attempted to reform astronomy to be reconciled with physics, especially the physics of Aristotle. His long commentary of Aristotle's Metaphysics describes the principles of his attempted reform, but later in his life he declared that his attempts had failed. He confessed that he had not enough time or knowledge to reconcile the observed planetary motions with Aristotelian principles. In addition, he did not know the works of Eudoxus and Callippus, and so he missed the context of some of Aristotle's astronomical works. However, his works influenced astronomer Nur ad-Din al-Bitruji (d. 1204) who adopted most of his reform principles and did succeed in proposing an early astronomical system based on Aristotelian physics. Physics In physics, Averroes did not adopt the inductive method that was being developed by Al-Biruni in the Islamic world and is closer to today's physics. Rather, he was—in the words of historian of science Ruth Glasner—a "exegetical" scientist who produced new theses about nature through discussions of previous texts, especially the writings of Aristotle. because of this approach, he was often depicted as an unimaginative follower of Aristotle, but Glasner argues that Averroes's work introduced highly original theories of physics, especially his elaboration of Aristotle's minima naturalia and on motion as forma fluens, which were taken up in the west and are important to the overall development of physics. Averroes also proposed a definition of force as "the rate at which work is done in changing