From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 34-35 |
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ʿAlī ibn
Khalaf: Abū al‐Ḥasan ibn Aḥmar al‐Ṣaydalānī
Roser Puig
Alternate
name
ʿAlī ibn Khalaf ibn Aḥmar
Akhīr [Akhiyar]
ʿAlī ibn Khalaf is
known for his work on “universal instruments.” No details of his biography
are known. In Arabic sources, he is only mentioned by Ṣāʿid al‐Andalusī in his Ṭabaqāt as an outstanding geometer,
who belonged, along with Zarqālī,
to a group of young Toledan scholars interested in philosophy.
There are several variants of his name. A footnote in Bū ʿAlwān's edition of
the Ṭabaqāt gives ʿAlī ibn Khalaf ibn
Aḥmar Akhīr (or
Akhiyar) al‐Ṣaydalānī. A very similar reading
quoted by an anonymous Egyptian 14th‐century source (preserved in Leiden,
Universiteitsbibliotheek, MS 468) is Abū al‐Ḥasan ʿAlī ibn Khalaf ibn Akhir (or Akhyar) bearing the title al‐Shajjārī,
the botanist. This has led D. A. King to identify him with Abū al‐Shajjār,
who is mentioned in Zarqālī's treatise on the ṣafīḥa
zarqāliyya (MS Escorial 962). King
also identifies him with ʿAlī al‐Shajjār,
who appears in a list of astronomers in the zīj of Ibn
Isḥāq
(13th century; Hyderabad, Andhra Pradesh, MS 298). According to this source,
ʿAlī ibn Khalaf determined
a value of 77° 13'
30" for the solar apogee, and he made an observation of the obliquity
of the ecliptic of 23° 32' 12". This observation was made in Toledo in 1084/1085 with the aid of
the physician, pharmacologist, and botanist Ibn Wāfid (died: 1075). Bearing
in mind Ibn Wāfid's date of death, this may not be a completely reliable
source.
ʿAlī ibn Khalaf is
the author of a treatise on the use of the lámina universal (universal
plate) preserved only in a Spanish translation included in the Libros del
Saber de Astronomía (III, 11–132), compiled by the Spanish King Alfonso
X. To our knowledge, the Arabic original is lost. ʿAlī ibn Khalaf is also credited with the construction of a universal
instrument called al‐asṭurlāb al‐maʾmūnī
in the year 1071, dedicated to al‐Maʾmūn, ruler of Toledo.
The universal
plate and the ṣafīḥa (the plate) of Zarqalī
(devised in 1048) are the first “universal instruments” (i. e., for
all latitudes) developed in Andalus. Both are based on the stereographic meridian
projection of each hemisphere, superimposing the projection of a half of the
celestial sphere from the vernal point (and turning it) on to the projection
of the other half from the autumnal point. However, their specific characteristics
make them different instruments.
In ʿAlī ibn Khalaf's
universal plate, the markings engraved on the mater correspond to longitudes
and latitudes of ecliptic coordinates. The horizontal diameter represents
the ecliptic, and the names of the zodiacal signs are engraved on the plate.
These markings also can be used in a way corresponding to the almucantars
and azimuthal circles of horizontal coordinates. The plate is fitted with
a rete. One half of it shows a hollowed‐out half‐set of markings
corresponding to the meridians and parallels of declination of equatorial
coordinates; the other half shows a selection of star pointers from the Northern
Hemisphere and the Southern Hemisphere. The rete is provided with two indexes.
Although there is no evidence of examples of that instrument, its influence
on the development of subsequent instruments has been suggested by E. Calvo.
Finally,
in the introduction to his treatise, ʿAlī
ibn Khalaf states his intention of writing a theoretical treatise on the several
possibilities of projecting the sphere. However, there is no evidence of the
existence of such a work.
Calvo, Emilia (1990). “La lámina universal de ʿAlī b. Jalaf (s.XI) en la versión alfonsí y su evolución en instrumentos
posteriores.” In “Ochava espera” y “Astrofísica”: Textos y estudios sobre
las fuentes árabes de la astronomía de Alfonso X, edited by Mercè Comes,
Honorino Mielgo, and Julio Samsó, pp. 221–238. Barcelona: Instituto “Millás
Vallicrosa” de Historia de la Ciencia Árabe.
King, David A. (1979). “On the Early History
of the Universal Astrolabe in Islamic Astronomy, and the Origin of the Term
Shakkāziyya in Medieval Scientific Arabic.” Journal
for the History of Arabic Science 3: 244–257. (Reprinted in King, Islamic
Astronomical Instruments, VII. London: Variorum
Reprints, 1987.)
——— (1997). “Shakkāziyya.”
In Encyclopaedia of Islam. 2nd ed. Vol. 9, pp. 251–253. Leiden: E. J. Brill.
Millás Vallicrosa,
José María (1943–1950). Estudios sobre Azarquiel. Madrid‐Granada.
——— (1944). “Un
ejemplar de azafea árabe de Azarquiel.” Al‐Andalus 9: 111–119.
Puig, Roser (1985).
“Instrumentos astronómicos universales hispano‐árabes.” In Instrumentos
astronómicos en la España medieval, su influencia en Europa, edited by
Juan Vernet et al., pp. 31–36, 90–97. Madrid.
——— (1992). “Instrumentos
universales en al‐Andalus.” In El legado científico andalusí, edited by Juan Vernet
et al., pp. 67–73, 228–239. Madrid.
Rico y Sinobas,
Manuel (1864). Libros del saber de astronomía del rey D. Alfonso X de Castilla,
copilados, anotados y comentados por Don Manuel Rico y Sinobas. Vol.
3, pp. 11–132. Madrid.
Ṣāʿid
al‐Andalusī (1985). Kitāb Ṭabaqāt
al‐umam, edited by Hayāt
Bū ʿAlwān. Beirut, 1935. (French translation with notes by Régis
Blachère as Livre des catégories des nations. Paris: Larose.)
Samsó, Julio
(1987). “Sobre el trazado de la azafea y de la lámina universal: Intervención
de los colaboradores alfonsíes.” Al‐Qantara 8: 29–43.
——— (1992).
Las ciencias de los antiguos en al‐Andalus. Madrid:
Mapfre.