The Jewish holidays are celebrated each year according to the Jewish calendar, thus fall on different Gregorian dates every year. The Jewish months are lunar-based, adjusted to the solar movements every two to three years (leap years).
Unlike the Gregorian calendar used by most of the world which arbitrarily sets the length of months to 28, 30 or 31 days, so it corresponds to the 365.5 days of the Solar year, the Jewish calendar coordinates the astronomical characteristics of our cosmological environment, the months are either 29 or 30 days corresponding with the 29Ā½-day lunar cycle, and the years are either 12 or 13 months, corresponding to the 12.4 month solar cycle.
As a result, some years we celebrate Chanukah around Thanksgiving time and other years closer to New Years Day, and the high holidays are upon us at times in early to mid September and other years Rosh Hashanah, Yom Kippur and Sukkot/Simchat Torah are celebrated in October. You can read more about the Jewish holidays at http://www.Mazornet.com/holidays/
