ISAAC IBN SID (ZAG; ÇAG):
Spanish astronomer; flourished at Toledo in the second half of the thirteenth century. From the surname "haḤazzan," given him by Isaac Israeli ("Yesod'Olam," iv. 30), it may be inferred that he was precentor at the synagogue. Isaac ibn Sid took a leading part in the compilation of the Alfonsine Tables. Isaac Israeli (ib.) states that he saw recorded in Isaac ibn Sid's own handwriting three observations of moon-eclipses made by him at the order of Alfonso. In official documents (De Castro, "Bibliotheca," i. 184b) Isaac ibn Sid is termed by Alfonso "our learned Rabbi Çag." In 1277 Isaac translated from the Arabic a work on the quadrant. His name is also connected with the invention of various instruments (De Castro, l.c. i. 144a, 156a, 157).
- Grätz, Gesch. vii. 115;
- Steinschneider, Hebr. Uebers. pp. 617 et seq.