Al-Zarqali (Arzachel) – Most famous for his “Book of Tables”

Abu Ishaq Ibrahim ibn Yahya al-Naqqash al-Zarqali (1029–1087), Latinized as Arzachel, also spelled Az-Zarqali, was a leading Arab mathematician and the foremost astronomer of his time. He lived in Toledo in Castile, Al-Andalus (now Spain)… His works inspired a generation of Islamic astronomers in Andalusia.

Az-Zarqali was not only just a Theoretical scientist but an inventor as well. His inventions and works put Toledo at the intellectual center of Al-Andalus. Al-Zarqali constructed the famed clocks of Toledo. The clocks were in use until 1135, when King Alfonso VI tried to discover how they worked and asked his soldiers to dismantle them. Once they were taken apart, nobody could reassemble them. They constituted a very precise lunar calendar and were, to some extent, the predecessors of the clocks or planetary calendar devices.See More

Astronomy:

Combining theoretical knowledge with technical skill, he excelled at the construction of precision instruments for astronomical use. He invented a the a flat astrolabe a device that was ‘universal,’ for it could be used at any lat…itude. This instrument came to be known as the Saphaea in Latin Europe.

Al-Zarqali also built a water clock capable of determining the hours of the day and night and indicating the days of the lunar months.

Al-Zarqali also wrote a treatise on the construction of an instrument (an equatorium) 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.”

Theory:

Al-Zarqali corrected Ptolemy’s geographical data, specifically the length of the Mediterranean Sea. He was the first to prove conclusively the motion of the aphelion relative to the fixed background of the stars. He measured its rate… of motion as 12.04 seconds per year, which is remarkably close to the modern calculation of 11.8 seconds.

He also contributed to the famous Tables of Toledo, a compilation of astronomical data of unprecedented accuracy. Al-Zarqali was famous as well for his own Book of Tables. Many “books of tables” had been compiled, but his almanac (Spanish-Arabic al manakh; “calendar”) contained tables which allowed one to find the days on which the Coptic, Roman, lunar, and Persian months begin, other tables which give the position of planets at any given time, and still others facilitating the prediction of solar and lunar eclipses.

He also compiled valuable tables of latitude and longitude. The was the first almanac in the modern sense, in that it was the first to provide entries that directly give “the positions of the celestial bodies and need no further computation”. The work provided the true daily positions of the sun, moon and planets for four years from 1088 to 1092, as well as many other related tables.See More

The crater Arzachel on the Moon is named after him.