"Alpetragius" redirects here. For
the lunar crater, see Alpetragius (crater).
Nur ad-Din al-Bitruji
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Died
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1204 AD
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ideas
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First non‐Ptolemaic
astronomical system; physical cause of celestial motions
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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 and
a Qadi from Al-Andalus.[1] Despite
his limited knowledge of Ptolemy's Almagest, al-Biṭrūjī
was the first astronomer after Ptolemy 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.[1]
The
crater Alpetragius on the Moon is named after him.
Life[edit]
Almost
nothing about his life is known, except that his name probably derives from Los Pedroches (al-Biṭrawsh),
a region nearCordoba.[1] He
was a disciple of Ibn Tufail (Abubacer)
and was a contemporary of Averroes.
Planetary model[edit]
Al-Bitruji
proposed a theory on planetary motion in which he wished to avoid both epicycles and
eccentrics,[2] and
to account for the phenomena peculiar to the wandering stars, by compounding rotations of
homocentric spheres. This was a modification of the system of planetary motion
proposed by his predecessors, Ibn Bajjah (Avempace)
and Ibn Tufail (Abubacer).
He was unsuccessful in replacing Ptolemy's planetary model, as the numerical
predictions of the planetary positions in his configuration were less accurate
than those of the Ptolemaic model,[3] because
of the difficulty of mapping Ptolemy's epicyclic model onto Aristotle's concentric spheres.
It
was suggested based on the Latin translations that his system is an update and
reformulation of that of Eudoxus of Cniduscombined 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.[1]
One
original aspects of al-Biṭrūjī's system is his proposal of a physical
cause of celestial motions. He combines the idea of "impetus" (first proposed by John Philoponus) 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.[1]
Works[edit]
Al-Bitruji
wrote Kitāb al-Hayʾah (The book of theoretical
astronomy/cosmology, Arabic, كتاب الهيئة),
which presented criticism of Ptolomy's Almagest 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 circles.[1]
This
work was translated into Latin by Michael Scot in
1217 as De motibus celorum [4] (first
printed in Vienna in
1531). A Hebrew translation by Moses ibn Tibbon was done in 1259.[1]
There
is also an anonymous treatise on tides (Escorial MS 1636, dated 1192) which
contains material seemingly borrowed from al-Bitruji.[1]
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