It reminds me of when I was a teenager and was when I was wisiting New York during Spring Vacation, the UN was closed because of a Muslim holiday. It was the Monday before Passover so I could look up what Muslim holiday fell around the Full Moon that Nissan. You also have to count how many leap years were between then (1999) and now. One way I can keep track of Ramadan is that it fell during Adar in 1994 because that is when Baruch Goldstein, ZT"L, HY"D killed the Arab terrorists in Hebron on Purim, which for the Muslims was a Friday in Ramadan that year. So to figure out when Ramadan was in a particular year, I know it was Adar that year and the next year Adar Aleph, after that Shevat until a Jewish leap year occurred pushing it to Tevet and so on until it is during Tammuz like this year. I have no idea what holiday was in Nissan that year, other than it was a few months 2 and a half months after Ramadan. It's hard to keep track of their holidays because they are as insane as the Koran itself. The Koran is arranged by number of verses in each chapter so the longest is either first or last (I don't remember.) rather than chronological and their calendar doesn't have a leap year so their holidays and months move throughout the year. Also, according to Islam, a person can be a few years older than they are by the Secular Calendar or the Jewish Calendar. I forget what the number is but it takes x amount of years for the months to be back in place at y (The season it was in in a particular year. So a person born in y will be a year older than x according to Islam when it is back in place.