and 17th centuries Al-Battānī's tables were used by the German mathematician Christopher Clavius in reforming the Julian calendar, leading to it being replaced by the Gregorian calendar in 1582. The astronomers Tycho Brahe, Giovanni Battista Riccioli, Johannes Kepler and Galileo Galilei cited Al-Battānī or his observations. His almost exactly correct value obtained for the Sun’s eccentricity is better than the values determined by both Copernicus and Brahe. The lunar crater Albategnius was named in his honour during the 17th century. Like many of the craters on the Moon's near side, it was given its name by Riccioli, whose 1651 nomenclature system has become standardized. In the 1690s, the English physicist and astronomer Edmund Halley, using Plato Tiburtius's translation of al-Battānī's , discovered that the Moon's speed was possibly increasing. Halley researched the location of Raqqa, where al-Battānī's observatory had been built, using the astronomer's calculations for the solar obliquity, the interval between successive autumnal equinoxes and several solar and lunar eclipses seen from Raqqa and Antioch. From this information, Halley derived the mean motion and position of the Moon for the years 881, 882, 883, 891, and 901. To interpret his results, Halley was dependent upon on knowing the location of Raqqa, which he was able to do once he had corrected the accepted value for the latitude of Aleppo. 18th century – present Al-Battānī's observations of eclipses were used by the English astronomer Richard Dunthorne to determine a value for the increasing speed of the Moon in its orbit, he calculated that the lunar longitude was changing at a rate of 10 arcseconds per century. Al-Battānī's data is still used by geophysicists. See also List of Arab scientists and scholars Notes References Sources (PDF version) Versions of manuscripts – Gerard of Abbeville Manuscript: Latin 16657 () 13761475 – Manuscript:Vat.lat.3098 () 14th century – Manuscript Latin 7266 () 19th, 20th century publications Further reading 929 deaths Year of birth uncertain 9th-century Arabs 10th-century Arabs 9th-century astrologers 9th-century astronomers 9th-century mathematicians 9th-century people from the Abbasid Caliphate 10th-century astrologers 10th-century astronomers 10th-century mathematicians Astronomers from the Abbasid Caliphate Astronomers of the medieval Islamic world Astrologers of the medieval Islamic world People from Harran Scientists who worked on qibla determination Mathematicians from the Abbasid Caliphate Sabian scholars from the Abbasid Caliphate