Editing Averroes (section)

=== Astronomy ===
As did [[Avempace]] and [[Ibn Tufail]], Averroes criticizes the [[Ptolemaic system]] using philosophical arguments and rejects the use of [[Orbital eccentricity|eccentrics]] and [[epicycles]] to explain the apparent motions of the Moon, the Sun and the planets. He argued that those objects move uniformly in a strictly circular motion around the Earth, following Aristotelian principles.{{sfn|Forcada|2007|pp=554–555}} He postulates that there are three type of planetary motions; those that can be seen with the naked eye, those that require instruments to observe and those that can only be known by philosophical reasoning.{{sfn|Iskandar|2008|p=1116}} Averroes argues that the occasional opaque colors of the Moon are caused by variations in its thickness; the thicker parts receive more light from the Sun—and therefore emit more light—than the thinner parts.{{sfn|Ariew|2011|p=193}} This explanation was used up to the seventeenth century by the European [[Scholasticism|Scholastics]] to account for [[Galileo]]'s observations of [[List of lunar features|spots]] on the Moon's surface, until the Scholastics such as Antoine Goudin in 1668 conceded that the observation was more likely caused by [[List of mountains on the Moon|mountains]] on the Moon.{{sfn|Ariew|2011|pp=194–195}} He and Ibn Bajja observed [[sunspot]]s, which they thought were [[Transit of Venus|transits of Venus]] and [[Transit of Mercury|Mercury]] between the Sun and the Earth.{{sfn|Vernet|Samsó|1996|p=264}} 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 [[Spherical Earth#Aristotle|Aristotle's argument]] for the [[spherical Earth]].{{sfn|Vernet|Samsó|1996|p=264}}

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.{{sfn|Vernet|Samsó|1996|p=266}} According to him, "the astronomy of our time offers no truth, but only agrees with the calculations and not with what exists."{{sfn|Agutter|Wheatley|2008|p=44}} 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.{{sfn|Arnaldez|1986|p=910}}{{sfn|Forcada|2007|pp=554–555}} He confessed that he had not enough time or knowledge to reconcile the observed planetary motions with Aristotelian principles.{{sfn|Forcada|2007|pp=554–555}} In addition, he did not know the works of [[Eudoxus of Cnidus|Eudoxus]] and [[Callippus]], and so he missed the context of some of Aristotle's astronomical works.{{sfn|Forcada|2007|pp=554–555}} 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.{{sfn|Vernet|Samsó|1996|pp=266–267}}