Ala Al-Din Abu'l-Hasan Ali Ibn Ibrahim Ibn al-Shatir
(1304 – 1375) (ابن الشاطر) was an Arab Muslim astronomer
who worked as muwaqqit
(موقت, religious timekeeper
) at the Umayyad Mosque
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
, 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.
While previous Maragha school models were just as accurate as the Ptolemaic 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. Other achievements of Ibn al-Shatir include the separation of natural philosophy from astronomy and the rejection of the Ptolemaic model on empirical rather than philosophical grounds. Unlike previous astronomers before him, Ibn al-Shatir was not concerned with adhering to the theoretical principles of cosmology or natural philosophy (or Aristotelian physics), but rather to produce a model that was more consistent with empirical observations. His model was thus in better agreement with empirical observations than any previous models produced before him. His work thus marked a turning point in astronomy, which may be considered a "Scientific Revolution before the Renaissance".
Unlike previous astronomers, Ibn al-Shatir generally had no philosophical objections against Ptolemaic astronomy, but was only concerned with how well it matched his own empirical
observations. He would usually test
the Ptolemaic models, and if any did not match his observations
, then he would formulate his own non-Ptolemaic model in its place which did match his observations. For example, it was Ibn al-Shatir's concern for observational accuracy which led him to eliminate the epicycle in the Ptolemaic solar model, as he describes below:
Ibn al-Shatir was also the earliest astronomer to introduce experiments into planetary theory, in order to test the Ptolemaic models on empirical grounds. For example, while testing the Ptolemaic solar model, Ibn al-Shatir "tested the Ptolemaic value for the apparent size of the solar disk by using lunar eclipse observations." His work on his experiments and observations, however, has not survived, but there are references to this work in his The Final Quest Concerning the Rectification of Principles.
Although his system was firmly geocentric
, he had eliminated the Ptolemaic equant
, and the mathematical details of his system were identical to those in Nicolaus Copernicus
' De revolutionibus
. His lunar model was also no different from the lunar model used by Copernicus. It is thus believed that Ibn al-Shatir's model was adapted by Copernicus into a 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.
Y. M. Faruqi writes:
Ibn al-Shatir invented the first astrolabic clock
in the early 14th century.
Ibn al-Shatir constructed a magnificent sundial
for the minaret
of the Umayyad Mosque
. As the ancient sundials
were nodus-based with straight hour-lines, they indicated unequal hours—also called temporary hours—that varied with the seasons. Every day was divided into twelve equal segments; thus, hours were shorter in winter and longer in summer. The idea of using hours of equal length throughout the year was the innovation of Abu'l-Hasan Ibn al-Shatir in 1371, based on earlier developments in trigonometry
by Muhammad ibn Jābir al-Harrānī al-Battānī
(Albategni). He was aware that "using a gnomon
that is parallel to the Earth's axis will produce sundials whose hour lines indicate equal hours on any day of the year." His sundial is the oldest polar-axis sundial still in existence. The concept later appeared in Western sundials from at least 1446.
The compass dial
, a timekeeping
device incorporating both a universal sundial
and a magnetic compass
, was invented by Ibn al-Shatir in the early 14th century.
, a multi-purpose astronomical instrument, was first constructed by Ibn al-Shatir. His compendium featured an alhidade
and polar sundial
among other things. These compendia later became popular in Renaissance
Ibn al-Shatir described another astronomical instrument which he called the "universal instrument" in his Rays of light on operations with the universal instrument
(Al-Ashi'a al-lāmi'a fī 'l-'amal bi-'l-āla al jāmi'a
). A commentary on this work entitled Book of Ripe Fruits from Clusters of Universal Instrument
(Kitab al-thimār al-yāni'a ‘an qutāf al-āla al-jāmi'a
) was later written by the Ottoman
astronomer and engineer Taqi al-Din
, who employed the instrument at the Istanbul observatory of al-Din
- Fernini, Ilias. A Bibliography of Scholars in Medieval Islam. Abu Dhabi (UAE) Cultural Foundation, 1998
- Kennedy, Edward S. "Late Medieval Planetary Theory." Isis 57 (1966):365-378.
- Kennedy, Edward S. and Ghanem, Imad. The Life and Work of Ibn al-Shatir, an Arab Astronomer of the Fourteenth Century. Aleppo: History of Arabic Science Institute, University of Aleppo, 1976.
- Roberts, Victor. "The Solar and Lunar Theory of Ibn ash-Shatir: A Pre-Copernican Copernican Model". Isis, 48(1957):428-432.
- Roberts, Victor and Edward S. Kennedy. "The Planetary Theory of Ibn al-Shatir". Isis, 50(1959):227-235.
- Saliba, George. "Theory and Observation in Islamic Astronomy: The Work of Ibn al-Shatir of Damascus". Journal for the History of Astronomy, 18(1987):35-43.
- Turner, Howard R. Science in Medieval Islam, an illustrated introduction. University of Texas Press, Austin, 1995. ISBN 0-292-78149-0 (pb) ISBN 0-292-78147-4 (hc)