The order of Moed (“appointed time”) provides specific instructions for the rituals, observances and laws related to holidays and festivals. “Moed” is the biblical word used to describe special days that are set apart from non-sacred days. The Torah prescribes six such sacred occasions: the weekly Sabbath, the Pilgrimage Festivals of Pesah (Passover), Sukkot (Tabernacles) and Shavuot (Pentecost), and what have become known as the High Holidays–Rosh Hashanah and Yom Kippur.
Additionally, the Mishnah in Seder Moed depicts the special days of Purim and as well as the 4 fast days. The absence of Hanukkah from this list has engendered considerable discussion, and may indicate the displeasure of the early Mishnah-era sages with the Maccabean dynasty.
The New Month and the Jewish Year
The Jewish year follows two coinciding rhythms. The first is the weekly cycle which frames life around the regular occurrence of the Sabbath. The other is the rhythm of the lunar calendar, which controls the timing of the months and the holidays. The lunar calendar follows the cycle of the moon as it waxes and wanes in the sky–each month beginning at the first sighting of the moon and lasting until the next sighting.
A month lasts either 29 or 30 days, and a full lunar year of 12 months consists of 354 days (give or take a day). Unlike the Muslim lunar calendar, however, the Jewish calendar maintains a relationship to the solar year. In order to ensure that Passover always occurs during the Spring, leap months are added seven times every nineteen years.
By the time of the Mishnah, the rabbis could calculate the lunar months precisely, but the calendar was still set according to the ancient tradition of relying on witnesses sighting the new moon. Consequently, the calendar always depended on the official declaration of the new month by the High Court in Jerusalem, which, in turn, determined the timing of the holidays.
As a result, the process of hearing the testimony of the witnesses and the declaration of the new month held great importance to the early Sages, as evident in the tractate of Rosh Hashanah, half of which is devoted to the intricacies of the seeing, reporting, and announcing of the new moon. However, in the fourth century, as Jewish communities were becoming less centralized, the sage Hillel II established a permanent Jewish calendar, thus breaking the link between the High Court and the calendar, but providing predictability to the dating of the Jewish holidays.