Ancient Torah Scroll
Beginning with Hanukkah, 2013, we have been posting brief explanations of the Jewish holidays on our home page at the time they are celebrated. Most are biblical holidays in the sense that they are observances required of Israel in the Old Testament. However, one is post-biblical, meaning that it originated after the close of the Old Testament canon. Hanukkah is a post-biblical feast because it commemorates the dedication of the Second Temple in 165 B.C. after its desecration by Antiochus Epiphanes.
The dates of these holidays are fixed on the Jewish calendar. For example, Passover always begins on the 15th of Nisan. However, the Jewish year is not the same length as a solar year, and thus the dates of the Jewish holidays shift from year to year on the standard solar calendar used in the Western world. It is also important to remember that in the Jewish world a new day begins at sunset.