The Islamic calendar is unique because it is lunar and so has 354 days, not 365 days. This means every year the calendar keeps shifting. That is the reason why Eid falls in different seasons over the years, returning to the same season almost 33 years later. Some say this is deliberate so as not to fix the time, so that one experiences the observances throughout the year at least twice in one’s lifetime--thrice, if one has a very long life. But these are matters of speculation.

The month of Muharram marks the first of twelve months of the Islamic calendar, and it has very different meanings for the Shia and the Sunni communities. The Shia and Sunnis are split on various issues. Shias have strong Mesopotamian influence, while Sunnis have strong Arabian influence.