The crescent moon, the sighting of which is important for the determination of when certain religious duties and practices must take place. The Quran says that new moons are “fixed seasons for humankind and for pilgrimage” ( 2:189 ). The need to determine the precise appearance of the hilal was one of the inducements for Muslim scholars to study astronomy. When it became apparent that sighting the new moon by the naked eye was not exact, some Muslims (primarily Ismailis) argued for calculating (hisab) the appearance of the new moon. The majority of Sunni Muslims have rejected calculation in favor of visual sighting.