a Series of Snacks

If you want to know when Chanukah is starting, it's easy: take the 25th day of Kislev, then assume the Hebrew calendar of 13 months, alternating 29 and 30 days, carefully adding 7 months every 19 years. Before Rosh Hashanah - which is in September if it isn't in October - add 3,761 years to the Christian date. After Rosh Hashanah but before January 1st, add one less. Then adjust the whole thing to be sure Tishri doesn't begin on a Friday or a Sunday, which would lengthen the Shabbos, or a Wednesday, which might possibly put Yom Kippur on a Friday, and there you have it. This is also one of the reasons we have trouble getting converts."