Another interesting wrinkle of the Islamic calendar is that (to put it in layman's terms) we don't even know the exact dates of the holidays until shortly beforehand, at which time a dude in Saudi Arabia announces that he's seen the requisite sliver of the moon which fixes the holiday's date. Allow me to explain, as per Wikipedia: "Traditionally, the first day of each month is the day (beginning at sunset) of the first sighting of the hilal (crescent moon) shortly after sunset. If the hilal is not observed immediately after the 29th day of a month (either because clouds block its view or because the western sky is still too bright when the moon sets), then the day that begins at that sunset is the 30th. Such a sighting has to be made by one or more trustworthy men testifying before a committee of Muslim leaders." I remember in Syria that there was often disagreement about whether the sighting had been made or not, which meant that sometimes our holidays there came a day after the holiday in Saudi Arabia.
You can imagine how fun it is to plan an academic calendar based on the sun while taking into consideration all the whims of a calendar based on the moon. AUS, for example, is constantly having to shift the first day of classes and all the other semester breaks in order to accommodate the Islamic holidays. And those holidays change dates every year, so your hard work one fall semester has to be thrown out the window the next.
For example, tomorrow (Thursday) is Islamic New Year - the beginning of the new cycle of the Islamic calendar. AUS has had it marked as a holiday since September. But until this morning, Miriam's school hadn't declared it as a day off (thankfully, they did).
Since I don't have to worry about planning academic calendars, I find the Islamic holidays extra festive because they change dates every year. Though I wonder how I would feel if (Northern Hemisphere) Western holidays did the same - would Halloween be the same without crisp fall air? What about Christmas without the possibility of snow? Easter without the rebirth of spring?
One more thing - along with the lunar calendar, Islam follows a different numbering of the years. Year one was AD 622 when Mohammed traveled from Mecca to Medina (the Hejira). So 2012 is actually 1433. In some other Arab countries we lived in, the alternate date was not very visible in society at large. Here, you see it listed on most official things - the dedication plaque of the library building, for example, lists both the Gregorian date and the Islamic one.
Anyway, Happy Islamic New Year! The more you know.