Nur Ed-Din Al Betrugi
Encyclopedia
Nur ad-Din al-Bitruji (also spelled Nur al-Din Ibn Ishaq Al-Betrugi and Abu Ishâk ibn al-Bitrogi; another spelling is al Bidrudschi) (known in the West by the Latinized name of Alpetragius) (died ca. 1204 AD) was an 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...

 and a Qadi
Qadi
Qadi is a judge ruling in accordance with Islamic religious law appointed by the ruler of a Muslim country. Because Islam makes no distinction between religious and secular domains, qadis traditionally have jurisdiction over all legal matters involving Muslims...

 from Al-Andalus
Al-Andalus
Al-Andalus was the Arabic name given to a nation and territorial region also commonly referred to as Moorish Iberia. The name describes parts of the Iberian Peninsula and Septimania governed by Muslims , at various times in the period between 711 and 1492, although the territorial boundaries...

. Despite his limited knowledge of Ptolomy's Almagest
Almagest
The Almagest is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths. Written in Greek by Claudius Ptolemy, a Roman era scholar of Egypt,...

, al-Biṭrūjī was the first astronomer after Ptolomy to present a non-Ptolemaic astronomical system as an alternative to Ptolemy's models. Another original aspect of his system was that he proposed a physical cause of celestial motions.

The crater Alpetragius
Alpetragius (crater)
Alpetragius is a lunar impact crater located on the eastern edge of Mare Nubium, to the southwest of the much larger crater Alphonsus. In the southeast is the prominent crater Arzachel, and to the west lies the flooded Lassell....

 on the 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...

 is named after him.

Life

Almost nothing about his life is known, except that his name probably derives from Los Pedroches
Los Pedroches
Los Pedroches or Valle de los Pedroches is a comarca in Córdoba Province, Andalusia, southern Spain. It is located at the northern end of the province. The main town is Pozoblanco.The climate of the comarca is continental...

 (al-Biṭrawsh), a region near Cordoba
Córdoba, Spain
-History:The first trace of human presence in the area are remains of a Neanderthal Man, dating to c. 32,000 BC. In the 8th century BC, during the ancient Tartessos period, a pre-urban settlement existed. The population gradually learned copper and silver metallurgy...

. He was a disciple of Ibn Tufail
Ibn Tufail
Ibn Tufail was an Andalusian Muslim polymath: an Arabic writer, novelist, Islamic philosopher, Islamic theologian, physician, vizier,...

 (Abubacer) and was a contemporary of Averroes
Averroes
' , better known just as Ibn Rushd , and in European literature as Averroes , was a Muslim polymath; a master of Aristotelian philosophy, Islamic philosophy, Islamic theology, Maliki law and jurisprudence, logic, psychology, politics, Arabic music theory, and the sciences of medicine, astronomy,...

.

Planetary model

Al-Bitruji proposed a theory on planetary motion in which he wished to avoid both epicycles and eccentrics
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...

, and to account for the phenomena peculiar to the wandering stars, by compounding rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...

s of homocentric spheres. This was a modification of the system of planetary motion proposed by his predecessors, Ibn Bajjah
Ibn Bajjah
Abū-Bakr Muhammad ibn Yahya ibn al-Sāyigh , known as Ibn Bājjah , was an Andalusian polymath: an astronomer, logician, musician, philosopher, physician, physicist, psychologist, botanist, poet and scientist. He was known in the West by his Latinized name, Avempace...

 (Avempace) and Ibn Tufail
Ibn Tufail
Ibn Tufail was an Andalusian Muslim polymath: an Arabic writer, novelist, Islamic philosopher, Islamic theologian, physician, vizier,...

 (Abubacer). He was unsuccessful in replacing Ptolemy
Ptolemy
Claudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...

's planetary model, as the numerical predictions of the planetary positions in his configuration were less accurate than those of the Ptolemaic model, because of the difficulty of mapping Ptolemy's epicyclic model onto Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

's concentric spheres.

One original aspects of al-Biṭrūjī's system is his proposal of a physical cause of celestial motions. He combines the idea of "impetus
Impetus
Impetus may refer to:* Impetus , a re-release of the EP Passive Restraints* Impetus , a concept very similar to momentum* Jean Buridan#Impetus Theory, middle-ages treatment on impetus and its originator Jean Buridan...

" (first proposed by John Philoponus
John Philoponus
John Philoponus , also known as John the Grammarian or John of Alexandria, was a Christian and Aristotelian commentator and the author of a considerable number of philosophical treatises and theological works...

) and the concept of shawq ("desire"), of Abū al‐Barakāt al‐Baghdādī, to explain how energy is transferred from a first mover placed in the 9th sphere to other spheres, explaining the other spheres' variable speeds and different motions. He contradicts the Aristotelian idea that there is a specific kind of dynamics for each world, applying instead the same dynamics to the sublunar and the celestial worlds.

It was suggested based on the Latin translations that his system is an update and reformulation of that of Eudoxus of Cnidus
Eudoxus of Cnidus
Eudoxus of Cnidus was a Greek astronomer, mathematician, scholar and student of Plato. Since all his own works are lost, our knowledge of him is obtained from secondary sources, such as Aratus's poem on astronomy...

 combined with the motion of fixed stars developed by al-Zarqālī. However, it is not known whether the Andalusian cosmologists had access or knowledge of Eudoxus works.

Works

Al-Bitruji wrote Kitāb al-Hayʾah (The book of theoretical astronomy/cosmology, Arabic, كتاب الهيئة), which presented criticism of Ptolomy's Almagest
Almagest
The Almagest is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths. Written in Greek by Claudius Ptolemy, a Roman era scholar of Egypt,...

from a physical point of view.
It was well known in Europe between the 13th and the 16th centuries, and was regarded as a valid alternative to Ptolemy's Almagest in scholastic
Scholasticism
Scholasticism is a method of critical thought which dominated teaching by the academics of medieval universities in Europe from about 1100–1500, and a program of employing that method in articulating and defending orthodoxy in an increasingly pluralistic context...

 circles.

This work was translated into Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 by Michael Scot
Michael Scot
Michael Scot was a medieval mathematician and scholar.- Early life and education :He was born in Scotland, and studied first at the cathedral school of Durham and then at Oxford and Paris, devoting himself to philosophy, mathematics, and astrology...

 in 1217 as De motibus celorum (first printed in Vienna
Vienna
Vienna is the capital and largest city of the Republic of Austria and one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.723 million , and is by far the largest city in Austria, as well as its cultural, economic, and political centre...

 in 1531). A Hebrew translation by Moses ibn Tibbon
Moses ibn Tibbon
Moses ibn Tibbon was a Jewish physician, author and translator. The number of works written by Moses ibn Tibbon makes it probable that he reached a great age....

 was done in 1259.

There is also an anonymous treatise on tides (Escorial MS 1636, dated 1192) which contains material seemingly borrowed from al-Bitruji.

Further reading

  • Helaine Selin, Encyclopaedia of the history of science, technology, and medicine in non western cultures, p. 160
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