Al-Zarqali (1029–1087)

Al-Zarqali known in the West as Arzachel, was a Spanish Muslim. He was a leading Muslim mathematician and astronomer of his time. He flourished in Toledo in Castile, now Spain.Arzachel crater on the Moon is named after him.

Al-Zarqali constructed a flat astrolabe – known as Safihah - that was 'universal,' for it could be used at any latitude, its details were published in Latin, Hebrew and several European languages.

Al-Zarqali constructed the famed water clock capable of determining the hours of the day and night and indicating the days of the lunar months.

He corrected the geographical data from Ptolemy and Al-Khwarizmi.Al-Zarqali corrected Ptolemy's estimate of the length of the Mediterranean Sea from 62 degrees to approximately correct value of 42 degrees.

Al-Zarqâli also wrote a treatise on the movement of the fixed stars, a discussion of theories regarding the solar year.

His astronomical observations were the best of his age, and enabled him to prove for the first time the motion of the solar apogee with reference to the stars .Motion of the solar apogee with reference to the stars which he said amounted to 12.04' a year; and also gave a value of 770 50' for the longitude of the sun's apogee, and concluded that the inclination of the ecliptic oscillated between 23033' and 23053'.

Al-Zarqali, however, is even more famed, and impacted for centuries on the Christian West with regard to his Toledan Tables .

Al-Zarqali carried out a series of astronomical observations at Toledo (Al Tulaytalah) and compiled them in what is known as his famous Toledan Tables. The tables include the determination of the right ascensions, and the equations of the sun and the moon and of the planets; parallax; eclipses, and the setting of the planets; theory of trepidation or accession and recession; etc . His work was translated into Latin by Gerard of Cremona, and was very popular for more than two centuries.

All subsequent tables for different locations in Europe were based on al-Zarqali's measurements. Raymond of Marseilles is one of the first who adapted Al-Zarqali's table to a European location, Marseilles.The tables of Marseilles (based on Al-Zarqali's Toledan Tables) were also adapted to the meridians of London, Paris and Pisa.

Al-Zarqali also wrote a treatise on the construction of an instrument (anequatorium) for computing the position of the planets using diagrams of the Ptolemaic model. This work was translated into Spanish in the 13th century by order of King Alfonso X in a section of the Libros del Saber de Astronomia entitled the "Libros de los laminas de los vii planetas."

Copernicus in his famous book 'De Revolutionibus Orbium Clestium' expresses his indebtedness to al-Battani (albategnius) and Al-Zarqali (Arzachel) and quotes their work several times.

Beer and Madler in their famous work Der Mond (1837) mention a surface feature of the moon after Al-Zarqali (Arzachel). It is a plain in the eighth section more than sixty miles in diameter and is surrounded by rows of mountains rising like terraces to heights of 13,000 feet above the interior region. It also includes several hills and craters and a prominent cleft by the side of the base of the western mountainous wall.