Rabbi, mathematician, astronomer, philosopher and biblical/talmudic commentator. In his Milchamot Hashem (Wars of the Lord) he elaborated on his own conception of Maimonides' philosophy as well as astronomy. His treatise contained 136 chapters, including a discussion of solar, lunar, and planetary motions with tables to aid in their computation and a discussion of the order of the planets and their distances from the earth. His writings influenced Copernicus and he is reputed to be the inventor of the "Jacob's Staff", a quadrant used for centuries by navigators.