Ibn al-Shatir  (1304 – 1375)

He was a muslim astronomer from Damascus who worked as timekeeper in the Umayyad Mosque, and constructed a magnificent sundial for its minaret in 1371/72.

Ibn al-Shatir

Ibn al-Shatir invented the first Astrolabic clock in the early 14th century.

His most important astronomical treatise was the Kitab nihayat al-sul fi tashih al-usul (The Final Quest Concerning the Rectification of Principles), in which he drastically reformed the Ptolemaic models of the Sun, Moon, and planets, by his introducing his own non-Ptolemaic models which eliminates the epicycle in the solar model, which eliminate the eccentrics and equant by introducing extra epicycles in the planetary models via the Tusi-couple, and which eliminates all eccentrics, epicycles and equant in the lunar model.

Ibn al-Shatir's geometrical model was the first that was actually superior to the Ptolemaic model in terms of its better agreement with empirical observations.

E. S. Kennedy discovered that Ibn al-Shatir's models were mathematically equivalent to those Copernicus elaborated some 150 years later.

"Whereas Ibn al-Shatir’s concept of planetary motion was conceived in order to play an important role in an earth-centred planetary model, Copernicus used the same concept of motion to present his sun-centred planetary model.

Ibn al-Shatir played the most significant role in the development of theoretical planetary models to account for the motions of the sun, moon, and planets and overcome the problems associated with Ptolemaic planetary models.

His lunar model was also no different from the lunar model used by Copernicus. This suggests that Ibn al-Shatir's model may have influenced Copernicus while constructing the heliocentric model. 

Though it remains uncertain how this may have happened, it is known that Byzantine Greek manuscripts containing the Tusi-couple which Ibn al-Shatir employed had reached Italy in the 15th century. 

It is also known that Copernicus'diagrams for his heliocentric model, including the markings of points, was nearly identical to the diagrams and markings used by Ibn al-Shatir for his geocentric model, making it very likely that Copernicus may have been aware of Ibn al-Shatir's work.

Another achievement of Ibn al-Shatir was the rejection of the Ptolemaic model on empirical rather than philosophical grounds.

Ibn al‐Shāṭir also compiled a set of tables displaying the values of certain spherical astronomical functions relating to the times of prayer.

The latitude used for these tables was 34°, corresponding to an unspecified locality just north of Damascus.

These tables display such functions as the duration of morning and evening twilight and the time of the afternoon prayer, as well as standard spherical astronomical functions.