Rosh Chodesh - The New Moon or "Beginning of the Month." The New Moon. In Talmudic times, the day of the New Moon was fixed by actual observation of the moon. As soon as it was visible, the Sanhedrin (Supreme Rabbinical Court) in Eretz Yisrael was informed. After ascertaining that the information was correct, the day of the New Moon (Rosh Chodesh) was announced. The fixed calendar. This system of direct observation was later discarded in favor of a more permanent method. Hillel II (c. 360 CE.) set up the fixed calendar, which is in use to the present day. The arrival of the New Moon is heralded in synagogue on the Sabbath before the new month (Shabbat Mevarchim). One or two Days. The Hebrew month may be of 29 or 30 days duration. When there are 29 days, Rosh Chodesh is observed on the first day of the new month. When there are 30 days, Rosh Chodesh is kept on the last day of the old month and the first day of the new month. Observance. There are no significant observances connected with Rosh Chodesh other than a few changes introduced into the liturgy (Liturgical additions: Recitation of Hallel, Yaale VeYavo; Torah Reading for Rosh Chodesh and Mussaf. ). There is, however, a tradition in certain pious circles for women to refrain from work on this day.