Ibn al-Shatir
Encyclopedia
Ala Al-Din Abu'l-Hasan Ali Ibn Ibrahim Ibn al-Shatir (1304 – 1375) was an Arab
Arab
Arab people, also known as Arabs , are a panethnicity primarily living in the Arab world, which is located in Western Asia and North Africa. They are identified as such on one or more of genealogical, linguistic, or cultural grounds, with tribal affiliations, and intra-tribal relationships playing...

 Muslim astronomer
Islamic astronomy
Islamic astronomy or Arabic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age , and mostly written in the Arabic language. These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and...

, mathematician
Islamic mathematics
In the history of mathematics, mathematics in medieval Islam, often termed Islamic mathematics or Arabic mathematics, covers the body of mathematics preserved and developed under the Islamic civilization between circa 622 and 1600...

, engineer and inventor
Inventions in the Islamic world
A number of inventions were developed in the medieval Islamic world, a geopolitical region that has at various times extended from Spain and Africa in the west to the Indian subcontinent in the east. The inventions listed here were developed during the medieval Islamic world, which covers the...

 who worked as muwaqqit (موقت, religious timekeeper
Timekeeper
A timekeeper is an instrument or person that measures the passage of time; in the case of the latter, often with the assistance of a clock or stopwatch...

) at the Umayyad Mosque
Umayyad Mosque
The Umayyad Mosque, also known as the Great Mosque of Damascus or formerly the Basilica of Saint John the Baptist , is located in the old city of Damascus, is one of the largest and oldest mosques in the world...

 in Damascus
Damascus
Damascus , commonly known in Syria as Al Sham , and as the City of Jasmine , is the capital and the second largest city of Syria after Aleppo, both are part of the country's 14 governorates. In addition to being one of the oldest continuously inhabited cities in the world, Damascus is a major...

, Syria
Syria
Syria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the West, Turkey to the north, Iraq to the east, Jordan to the south, and Israel to the southwest....

.

Astronomy

Theory

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
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

, Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

, and planets, by his introducing his own non-Ptolemaic models which eliminates the epicycle
Deferent and epicycle
In the Ptolemaic system of astronomy, the epicycle was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets...

 in the solar model, which eliminate the eccentrics and equant
Equant
Equant is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of heavenly bodies....

 by introducing extra epicycles in the planetary models via the Tusi-couple
Tusi-couple
The Tusi-couple is a mathematical device in which a small circle rotates inside a larger circle twice the diameter of the smaller circle. Rotations of the circles cause a point on the circumference of the smaller circle to oscillate back and forth in linear motion along a diameter of the larger...

, and which eliminates all eccentrics, epicycles and equant in the lunar model
Lunar theory
Lunar theory attempts to account for the motions of the Moon. There are many irregularities in the Moon's motion, and many attempts have been made over a long history to account for them. After centuries of being heavily problematic, the lunar motions are nowadays modelled to a very high degree...

.

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
Empirical
The word empirical denotes information gained by means of observation or experimentation. Empirical data are data produced by an experiment or observation....

 observation
Observation
Observation is either an activity of a living being, such as a human, consisting of receiving knowledge of the outside world through the senses, or the recording of data using scientific instruments. The term may also refer to any data collected during this activity...

s . Another achievement of Ibn al-Shatir was 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
Cosmology
Cosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order...

 or natural philosophy
Natural philosophy
Natural philosophy or the philosophy of nature , is a term applied to the study of nature and the physical universe that was dominant before the development of modern science...

 (or Aristotelian physics
Aristotelian physics
Aristotelian Physics the natural sciences, are described in the works of the Greek philosopher Aristotle . In the Physics, Aristotle established general principles of change that govern all natural bodies; both living and inanimate, celestial and terrestrial—including all motion, change in respect...

), but rather to produce a model that was more consistent with empirical
Empirical
The word empirical denotes information gained by means of observation or experimentation. Empirical data are data produced by an experiment or observation....

 observations. His model was thus in better agreement with empirical observation
Observation
Observation is either an activity of a living being, such as a human, consisting of receiving knowledge of the outside world through the senses, or the recording of data using scientific instruments. The term may also refer to any data collected during this activity...

s 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".

Testing

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
Empirical
The word empirical denotes information gained by means of observation or experimentation. Empirical data are data produced by an experiment or observation....

 observations. He employed careful observations of the diameters of the Sun and Moon to test the Ptolemaic models on empirical grounds, testing "the Ptolemaic value for the apparent size of the solar disk by using lunar eclipse
Lunar eclipse
A lunar eclipse occurs when the Moon passes behind the Earth so that the Earth blocks the Sun's rays from striking the Moon. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, a lunar eclipse can only occur the night of a...

 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.

As a consequence of his observation
Observation
Observation is either an activity of a living being, such as a human, consisting of receiving knowledge of the outside world through the senses, or the recording of data using scientific instruments. The term may also refer to any data collected during this activity...

s, he formulated his own modification of the Ptolemaic model. Ibn al-Shatir's concern with the observed solar diameter led him to replace Ptolemy's epicycle and equant
Equant
Equant is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of heavenly bodies....

 solar model with a model using three spheres, a large sphere centered on the Earth which he called the parecliptic, a smaller sphere carried by the pareclptic, which he called the deferent, and an even smaller sphere carried by the deferent, which he called the director. The Sun was then carried by the director.

Influence

Although his system was firmly geocentric, he had eliminated the Ptolemaic equant
Equant
Equant is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of heavenly bodies....

 and eccentrics, and the mathematical details of his system were identical to those in Nicolaus Copernicus
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....

' De revolutionibus. 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
Copernican heliocentrism
Copernican heliocentrism is the name given to the astronomical model developed by Nicolaus Copernicus and published in 1543. It positioned the Sun near the center of the Universe, motionless, with Earth and the other planets rotating around it in circular paths modified by epicycles and at uniform...

. Though it remains uncertain how this may have happened, it is known that Byzantine Greek manuscripts containing the Tusi-couple
Tusi-couple
The Tusi-couple is a mathematical device in which a small circle rotates inside a larger circle twice the diameter of the smaller circle. Rotations of the circles cause a point on the circumference of the smaller circle to oscillate back and forth in linear motion along a diameter of the larger...

 which Ibn al-Shatir employed had reached Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

 in the 15th century. It is also known that Copernicus' diagram
Diagram
A diagram is a two-dimensional geometric symbolic representation of information according to some visualization technique. Sometimes, the technique uses a three-dimensional visualization which is then projected onto the two-dimensional surface...

s for his heliocentric model, including the markings
Annotation
An annotation is a note that is made while reading any form of text. This may be as simple as underlining or highlighting passages.Annotated bibliographies give descriptions about how each source is useful to an author in constructing a paper or argument...

 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:

Polar-axis sundial

Ibn al-Shatir constructed a magnificent sundial
Sundial
A sundial is a device that measures time by the position of the Sun. In common designs such as the horizontal sundial, the sun casts a shadow from its style onto a surface marked with lines indicating the hours of the day. The style is the time-telling edge of the gnomon, often a thin rod or a...

 for the minaret
Minaret
A minaret مناره , sometimes مئذنه) is a distinctive architectural feature of Islamic mosques, generally a tall spire with an onion-shaped or conical crown, usually either free standing or taller than any associated support structure. The basic form of a minaret includes a base, shaft, and gallery....

 of the Umayyad Mosque
Umayyad Mosque
The Umayyad Mosque, also known as the Great Mosque of Damascus or formerly the Basilica of Saint John the Baptist , is located in the old city of Damascus, is one of the largest and oldest mosques in the world...

 in Damascus
Damascus
Damascus , commonly known in Syria as Al Sham , and as the City of Jasmine , is the capital and the second largest city of Syria after Aleppo, both are part of the country's 14 governorates. In addition to being one of the oldest continuously inhabited cities in the world, Damascus is a major...

 which gave both seasonal and equinoctial hours. The fragments of this sundial in a Damascus museum make this the oldest polar-axis sundial still in existence.

Time keeping device

He devised a time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

keeping device incorporating both a universal sundial
Sundial
A sundial is a device that measures time by the position of the Sun. In common designs such as the horizontal sundial, the sun casts a shadow from its style onto a surface marked with lines indicating the hours of the day. The style is the time-telling edge of the gnomon, often a thin rod or a...

 and a magnetic compass
Compass
A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...

.

Compendium

The compendium
Compendium
A compendium is a concise, yet comprehensive compilation of a body of knowledge. A compendium may summarize a larger work. In most cases the body of knowledge will concern some delimited field of human interest or endeavour , while a "universal" encyclopedia can be referred to as a compendium of...

, a multi-purpose astronomical instrument, was first constructed by Ibn al-Shatir. His compendium featured an alhidade
Alhidade
An alidade is a device that allows one to sight a distant object and use the line of sight to perform a task. This task can be, for example, to draw a line on a plane table in the direction of the object or to measure the angle to the object from some reference point...

 and polar sundial
Sundial
A sundial is a device that measures time by the position of the Sun. In common designs such as the horizontal sundial, the sun casts a shadow from its style onto a surface marked with lines indicating the hours of the day. The style is the time-telling edge of the gnomon, often a thin rod or a...

 among other things. These compendia later became popular in Renaissance
Renaissance
The Renaissance was a cultural movement that spanned roughly the 14th to the 17th century, beginning in Italy in the Late Middle Ages and later spreading to the rest of Europe. The term is also used more loosely to refer to the historical era, but since the changes of the Renaissance were not...

 Europe.

Universal instrument

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
Ottoman Empire
The Ottoman EmpireIt was usually referred to as the "Ottoman Empire", the "Turkish Empire", the "Ottoman Caliphate" or more commonly "Turkey" by its contemporaries...

 astronomer and engineer Taqi al-Din, who employed the instrument at the Istanbul observatory of Taqi al-Din from 1577-1580.

External links

(PDF version)
  • http://faculty.kfupm.edu.sa/phys/alshukri/PHYS215/Islamic%20astronomy.htm
  • http://www.riifs.org/review_articles/review_v1no2_sliba.htm
  • http://www.angelfire.com/il/Fernini/ifscience.html
  • http://www.cs.sfu.ca/~anoop/weblog/archives/000080.html
  • http://www.bookrags.com/research/ala-al-din-abul-hasan-ali-ibn-ibrah-scit-021234/
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