 Later, the "Zij-i Ilkhani" compiled at the Maragheh observatory sets the precession of the equinoxes at 51 arc seconds per annum, which is very close to the modern value of 50.2 arc seconds.In the Middle Ages, Islamic and Latin Christian astronomers treated "trepidation" as a motion of the fixed stars to be "added to" precession.This theory is commonly attributed to the Arab astronomer Thabit ibn Qurra, but the attribution has been contested in modern times.