Albategnius (Al-Battani, Muhammad ibn-Jabir) (c.858–929)
Albategnius, an Arab prince born in Batan, Mesopotamia, was the leading astronomer and mathematician of his time. He drew up improved tables of the Sun and Moon, measured the eccentricity of Earth's orbit and the inclination of Earth's equator to its orbital plane, and derived an accurate length for the year, which was used in the Gregorian reform of the Julian calendar.
His observations at Rakku, made over a 40-year period, were summarized in De Numeris Stellarum et Motibus (Movements of the Stars), first published in Europe in 1537, and enabled Hevelius to discover the secular variation in the Moon's motion. In mathematics, Al-Battani introduced the use of signs.