Itzḥak ben Shlomo ibn al-Aḥdab (or ibn al-Ḥadib) ben Tzaddiq ha-Sefardi (, c. 1350 – c. 1426) was a
Jew
Jews (, , ), or the Jewish people, are an ethnoreligious group and nation, originating from the Israelites of ancient Israel and Judah. They also traditionally adhere to Judaism. Jewish ethnicity, religion, and community are highly inte ...
ish mathematician, astronomer, and poet.
Ibn al-Aḥdab was born in Castile to a prominent Jewish family. He was a student of Judah ben Asher II, the great-grandson of Asher ben Yeḥiel of Cologne, who was killed in the anti-Jewish massacres of 1391. By 1396 Ibn al-Aḥdab had fled Spain and was in
Sicily
Sicily (Italian language, Italian and ), officially the Sicilian Region (), is an island in the central Mediterranean Sea, south of the Italian Peninsula in continental Europe and is one of the 20 regions of Italy, regions of Italy. With 4. ...
, where he lived (in
Syracuse
Syracuse most commonly refers to:
* Syracuse, Sicily, Italy; in the province of Syracuse
* Syracuse, New York, USA; in the Syracuse metropolitan area
Syracuse may also refer to:
Places
* Syracuse railway station (disambiguation)
Italy
* Provi ...
and
Palermo
Palermo ( ; ; , locally also or ) is a city in southern Italy, the capital (political), capital of both the autonomous area, autonomous region of Sicily and the Metropolitan City of Palermo, the city's surrounding metropolitan province. The ...
) until his death around 1426.
Work
He studied the algebra of Maghrebi mathematician Ibn al-Bannā and published ''The Epistle of the Number'', a translation and detailed commentary on Ibn al-Bannā's 13th century treatise ''Talḵīṣ ʿAmal al-Ḥisāb'' ("A summary of the operations of calculation"). The work is notable in being the first known Hebrew-language treatise to include extensive algebraic theories and operations.
His astronomical works include ''Oraḥ selulah (Upraised Path)'', a set of tables in Hebrew for conjunctions and oppositions of the Sun and the Moon, ''Keli Ḥemdah (Precious Instrument),'' which describes a unique
equatorium
An equatorium (plural, equatoria) is an astronomy, astronomical Mechanical calculator, calculating instrument. It can be used for finding the positions of the Moon, Sun, and planets without arithmetic operations, using a geometrical model to re ...
of his own invention, functioning on the Ptolemaic theory of epicycles,'''' and ''Keli Memutsa (Intermediate Instrument)'', which describes another unique instrument of his own design, a combination
astrolabe
An astrolabe (; ; ) is an astronomy, astronomical list of astronomical instruments, instrument dating to ancient times. It serves as a star chart and Model#Physical model, physical model of the visible celestial sphere, half-dome of the sky. It ...
-
quadrant
Quadrant may refer to:
Companies
* Quadrant Cycle Company, 1899 manufacturers in Britain of the Quadrant motorcar
* Quadrant (motorcycles), one of the earliest British motorcycle manufacturers, established in Birmingham in 1901
* Quadrant Privat ...
''.''
Bernard R. Goldstein
Bernard Raphael Goldstein (born January 29, 1938) is a historian of science and professor emeritus at the University of Pittsburgh. Goldstein published on the history of astronomy in medieval Islamic and Jewish civilization and early modern times. ...
published a partial translation of ''Keli Ḥemdah'' in 1987. ''Oraḥ selulah'' survives in 25 MSS, ''Keli Ḥemdah'' in 15 MSS, and ''Keli Memutsa'' in 1 MS.
He is the author of a commentary on the
Passover Haggadah
The Haggadah (, "telling"; plural: Haggadot) is a foundational Jewish text that sets forth the order of the Passover Seder. According to Jewish practice, reading the Haggadah at the Seder table fulfills the mitzvah incumbent on every Jew to rec ...
, titled ''Pesach Doros'' (''Passover of later generations)'' and printed by Mekhon Bet Aharon ṿe-Yiśraʼel in 2000.
''Leshon ha-Zahav (Golden Language)'', an explication of the names for units and measurements found in the
Hebrew Bible
The Hebrew Bible or Tanakh (;"Tanach" . ''
He is probably the author of a commentary on
Maimonides
Moses ben Maimon (1138–1204), commonly known as Maimonides (, ) and also referred to by the Hebrew acronym Rambam (), was a Sephardic rabbi and Jewish philosophy, philosopher who became one of the most prolific and influential Torah schola ...
' '' Laws of the Sanctification of the Month,'' found in the same MS as ''Leshon ha-Zahav'' with no author given.
He also wrote songs, published as ''Shirei Rabbeinu Itzḥak ben Shlomo ibn al-Aḥdab'' (1987). He is known to have composed a work called ''Shir ha-Shirim,'' but it has not survived.