Albategnius Crater (2)

Albategnius (Al-Battani, Muhammad ibn Jabir) (approx. 850-929)
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An Iraqi prince, born in Batan, Mesopotamia (Iraq), who 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. He was capable of making an extremely accurate measurement of the length of the Earth year - which was also used in the Gregorian reform of the Julian Calendar. His observations at Rakku, made over (probably) a 40-year period, were summarized in his work "Movements of the Stars" (first published in Europe in 1537).
Thanks to his contribution, Johannes Hevelius (1611-1687) was able to theorize and discover the secular variation in the Moon’s motion.