Itzḥak ben Shlomo ibn al-Aḥdab (or ibn al-Ḥadib) ben Tzaddiq ha-Sefardi ( he, יצחק בן שלמה בן צדיק אלאחדב הספרדי, c. 1350 – c. 1426) was a

Jew Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""Th ...

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 (man) it, Siciliana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Ethnicity , demographics1_footnotes = , demographi ...

, where he lived (in

Syracuse Syracuse may refer to: Places Italy *Syracuse, Sicily, or spelled as ''Siracusa'' *Province of Syracuse United States *Syracuse, New York **East Syracuse, New York **North Syracuse, New York *Syracuse, Indiana * Syracuse, Kansas *Syracuse, Miss ...

and

Palermo Palermo ( , ; scn, Palermu , 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 ...

) 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 astronomical calculating instrument. It can be used for finding the positions of the Moon, Sun, and planets without arithmetic operations, using a geometrical model to represent the position of a given c ...

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 ( grc, ἀστρολάβος ; ar, ٱلأَسْطُرلاب ; persian, ستاره‌یاب ) is an ancient astronomical instrument that was a handheld model of the universe. Its various functions also make it an elaborate inclin ...

- quadrant''.''

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 ( he, הַגָּדָה, "telling"; plural: Haggadot) is a Jewish text that sets forth the order of the Passover Seder. According to Jewish practice, reading the Haggadah at the Seder table is a fulfillment of the mitzvah to each Jew ...

, 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"
''Random House Webster's Unabridged Dictionary''. Hebrew: ''Tān ...

. He is probably the author of a commentary on

Maimonides Musa ibn Maimon (1138–1204), commonly known as Maimonides (); la, Moses Maimonides and also referred to by the acronym Rambam ( he, רמב״ם), was a Sephardic Jewish philosopher who became one of the most prolific and influential Torah ...

' '' 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.

References

{{Authority control 1350s births 1420s deaths 14th-century astronomers 14th-century mathematicians 14th-century Castilian Jews 15th-century Spanish astronomers 15th-century Spanish mathematicians 15th-century Spanish Jews Medieval Jewish astronomers