Lunar_calendar lunar calendar is a calendar that is based on cycles of the moon phase. The only widely used purely lunar calendar is the Islamic calendar or Hijri calendar, whose year always consists of 12 lunar months. A feature of a purely lunar year, on the Islamic calendar model, is that the calendar ceases to be linked to the seasons, and drifts each year by 11 days (or 12 days in case of leap year), and comes back to the position it had in relation to the solar year approximately every 33 Islamic years.