Spanish astronomer; flourished at Toledo in the second half of the thirteenth century. From the surname "haḤazzan," given him by Isaac Israeli ("Yesod'Olam," 4:30), 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," 1:184b) 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, c. 1:144a, 156a, 157).