Islamic calendar
While Arbaʽein is always on nearly the same day (20 or 21 Safar) of the Islamic calendar, the date on the Gregorian calendar varies from year to year because of differences between the two calendars, since the Islamic calendar, the Hijri calendar (AH), is a lunar calendar and the Gregorian calendar is a solar calendar. Furthermore, the method used to determine when each Islamic month begins varies from country to country (see Islamic calendar).