No. Easter doesn’t go from December to September. In 1999, Ramadan started in December that year ‘till January the next. Since then, it’s crept back several months. Easter doesn’t do that...
I think Muslims use a different calendar. So do Jews and various other religious groups.
The Islamic calendar is a 12 month lunar calendar of 354 or 355 days. So it moves when compared to a Gregorian calendar ten or eleven days a year.
The current Year of the Hijra is 1431. It began on December 18th, 2009 and will end on December 6th, 2010.
http://en.wikipedia.org/wiki/Islamic_calendar
I should have been clearer. Different religions use different calendars for calculating religious events. Christians and Jews use a very similar one, although Western and Easter Christians disagree over the correct date for Easter in relationship to the Jewish calendar - upon which the date of Easter is based.
However, secular calendars in the West, which are used by everybody, have been revised several times to make up for discrepancies that led to signifcant date shifts. Most people in the West accepted this, although certain groups (Old Calendar Orthodox, for example) were essentially going by the Julian calendar, which predated the current Gregorian calendar introduced in the 16th century that is now used as the universal civil calendar.
The Muslims, being from the ME and not part of Western changes, continued with their own calculations of time. I don’t know much about it and really can’t tell you why it shifts so.
Easter has gone from May to March, 3 months. December to September is 4 months, not that big of a difference.
So what is the limit on what is OK and why do you care?