Al-Zarqali

Al-Zarqali observed the Sun for twenty-five years from 1050, and published his results in works written in Arabic and translated into Latin, Hebrew and Castilian. His almanac, composed between 1088 and 1092, gave the true daily positions of the Sun for those years. He was the first astronomer to demonstrate the motion of the solar apogee relative to the fixed stars, measuring it at 12.04 arc-seconds per year - strikingly close to the modern figure of 11.77 ¹.

His most famous invention was the universal astrolabe plate that carries his name, the safiha zarqaliyya (Latin: Saphaea). Unlike an ordinary astrolabe, whose plates must be swapped for each latitude, his plate worked at any latitude, which made it a practical instrument for navigators; it remained in use into the 16th century. He wrote a treatise on its construction and use, later translated into Latin by Bernard of Aragon ¹.

Al-Zarqali contributed to the Toledan Tables, and revised al-Khwarizmi's astronomical tables, recomputing many of their longitudes from the meridian of Toledo. Against Ptolemy, he measured the length of the Mediterranean as 42 degrees rather than Ptolemy's 62 - much nearer the modern value. Studying Mercury, he noted that the centre of its eccentric deferent traces an oval, rather than a circular, path ¹².

When Alfonso VI of Castile took Toledo in 1085, al-Zarqali fled; whether he settled in Cordoba or died at Mocejón or in a refugee camp is not known. Modern references give his death as 1100 at Cordoba, while older references - and one of the two dates carried by Wikidata - give 1087; this record follows 1100 and flags the disagreement ¹³.