Abu al-Hasan al-Marrakushi

Of the man himself, the biographers kept nothing — no birth year, no teachers, no court appointment. What stands is his name, Abu Ali al-Hasan al-Marrakushi, carrying Marrakesh in it; a migration east from the Maghrib to Cairo in a century of upheaval; and the book. The archive holds him in the honest frame: he flourished in Cairo in the second half of the thirteenth century, and his own pages show him still at work in 1282.

The book is the Jami' al-mabadi' wa-l-ghayat fi 'ilm al-miqat — the Collection of Principles and Objectives in the Science of Timekeeping — written between 1276 and 1282, in four parts: the calculations, from chronology to spherical astronomy and the hours of prayer; the construction of instruments, sundials and quadrants and the projections of the sphere; their use; and, last, a master's quiz to prove the student. Modern scholarship calls it the most complete surviving source on the astronomical instruments of medieval Islam, and — in David King's judgment — the standard reference of the timekeeping profession from Mamluk Cairo and Rasulid Yemen to Ottoman Istanbul.

One personal trace survives, and it is a journey. His table of one hundred and thirty-five localities marks forty-four latitudes in red — the ones he measured himself, on the ground, from the Atlantic Sahara along the Maghrib and the Mediterranean shore to Egypt: a man who crossed the top of Africa measuring the sky as he went. His star table stands computed for the year 1281-82.

His death is bracketed only between 1282 and about 1320, most probably at Cairo. Sédillot's French translation of 1834 carried the book into European scholarship, and a crater on the Moon now bears his name. Honored be al-Hasan al-Marrakushi, who left no biography and needed none — the sky he measured is the record.