Abraham bar Chiyya lived during the first part of the 12th century in Barcelona. He was a multi-talented rabbi. He was a philosopher, astronomer, mathematician, surveyor, astrologer, and interpreter, possessing exactly the skills needed by the conquering Christian kings. He served as a court functionary and was also given authority within the Jewish community.
Bar Chiyya's philosophic endeavors focused on two different questions. He was interested in how the world was created, and he was interested in figuring out when the end of time would take place. His book on the subject, Megillat Ha-Megalleh was the first eschatological book written by a European rabbi. According to his calculations, the world would be redeemed in 1383, and resurrection would take place in 1448. He had a powerful influence on subsequent scholars and astrologers.
Abraham bar Chiyya was the author of the first major book of mathematics written in Hebrew. He also sent a treatise to the Jews of France to help them with their measurements of fields. He thus introduced Arabic trigonometry to the West. This treatise was the first Hebrew work to introduce the concept of pi and show how it could be used to find the area of a circle.
Abraham bar Chiyya's astronomical works included a major work on the earth's geography and a major treatise on intercalation. His computations were considered authoritative.
Abraham bar Chiyya was a contemporary of Rabbi Judah bar Barzillai, with whom he had a public disagreement. Bar Chiyya wanted a wedding postponed because the astrological signs were not positive. Judah bar Barzillai refused because he viewed astrology to be illegal in Jewish tradition. The two exchanged letters on this topic.
Sources: Gates to Jewish Heritage