[pl. Roshei Chodoshim]; beginning of a month, marked by the “molad,” or the “New Moon. Rosh Chodesh is intimately tied to the life of the Jew. Just as the visible portion of the moon grows to its full roundness and then declines to invisibility, so is it for the People of Israel. At times, such as at the time of Kings David and Solomon, Jewish fortunes were extremely bright; at other times, such as during the times of Roman persecution, or the Nazi Holocaust, Jewish fortunes were at a very low ebb.
The Hebrew Calendar is basically a lunar one, determined by the testimony of witnesses as to their observations of the New Moon.
“Rosh Chodesh” is considered a minor holiday, sometimes marked, as in the time of King Shaul with a festive meal, and a time for atonement. As we say in a Prayer dedicated to Rosh Chodesh, “You have given to Your People the celebration of New Months, a time for Atonement for all their generations.”
The beginning of a particular month of the twelve (or, less frequently, thirteen), is either one or two days, depending on whether the previous month was “malei,” full; i.e. 30 days, or “chaser,” lacking; i.e. only 29 days. In the case where the preceding month had thirty days, the “Rosh Chodesh” of the current month consists of two days: the 30th day of the previous month AND the first day of the current month. In the case where the preceding month had only twenty nine days, the “Rosh Chodesh” of the current month consists of just one day; namely, ONLY the first day of the current month.