The Significance of Rosh Chodesh: A New Month in the Jewish Calendar

What is Rosh Chodesh? Rosh Chodesh marks the beginning of the Hebrew month. It is the first day of every Hebrew month, and in months with thirty days, the last day is also considered Rosh Chodesh for the following month. The announcement of Rosh Chodesh is vital for determining Jewish holidays, as they are based on the Hebrew calendar.

Why is it important? According to the *Mishnah* in *Masechet Rosh Hashanah*, during the period when the Hebrew calendar was established based on the sighting of the new moon, Rosh Chodesh was determined by the *Sanhedrin*, who would investigate witnesses who claimed to have seen the new moon. If the testimony was confirmed, the judges would announce the sanctification of the month with the phrase "*Mekudash, Mekudash*". They would then relay this news to all Jewish communities in the land and abroad by lighting beacons on mountain tops. At one point, the Samaritans lit their own beacons, disrupting the message transmission, leading to the establishment of sending messengers for the announcement of the month (*Rosh Hashanah*, Chapter 2, *Mishnah* 7).

The crucial importance of announcing the date of Rosh Chodesh is significant since, based on the months, the timing of each holiday could be calculated. A miscommunication regarding when Rosh Chodesh occurs could lead Jews to eat *chametz* on *Pesach* or fail to fast on *Yom Kippur*.

In modern times, Rosh Chodesh is predetermined by the calendar established by *Hillel II*. This calendar consists of a 19-year cycle that aligns the solar and lunar cycles. Therefore, as a remembrance of the *Kiddush HaChodesh* practiced in the Temple, synagogues announce Rosh Chodesh on the Shabbat preceding it, mentioning the day of the week on which it will occur. Some have the custom to fast on the day before Rosh Chodesh, known as *Yom Kipur Katan*.

A final thought. In biblical times and during the era of the *Chazal*, Rosh Chodesh was observed as a day of rest, similar to a holiday, and special *Musaf* offerings were brought to the Temple. However, today, the differences of Rosh Chodesh from other days are minimal, aside from the addition of the *Musaf* prayer and *Ya’aleh V’yavo* during prayers and blessings. Nevertheless, there are various customs observed in Jewish communities on this day: in Sephardic communities, some recite the chapter "*Barchi Nafshi*" before the evening prayer of Rosh Chodesh, some women light candles on the evening of the day, and many wear clean garments (like white shirts) to feel the distinction between this day and the others.