The Book of Intercalation: On the Christian Calendar

Abraham bar Ḥiyya was a philosopher, mathematician, and scientist who lived in Barcelona. He apparently held a position of leadership recognized by both Jewish and non-Jewish communities, but the details are not precisely known. His The Foundations of Understanding and the Tower of Faith (Yesode ha-tevunah u-migdal ha-emunah) was the first Hebrew encyclopedia of science; only the introduction and part of the first treatise are extant. In that and other works, he attempted to render Arabic and Greek scientific terms in Hebrew, thus shaping the evolution of the Hebrew language in the medieval period. Bar Ḥiyya was interested in astrology and once sought to postpone a wedding because the stars were not properly aligned, a position that led to a clash with Judah Barzillai, also of Barcelona. Bar Ḥiyya’s penchant for astrology also manifested itself in detailed eschatological speculations in The Scroll of the Revealer (Megilat ha-megaleh); he deduced that the redemption would arrive in 1383 and that the resurrection of the dead would take place in 1448.