In Judaism, Rosh Chodesh or Rosh Hodesh (; trans. Beginning of the Month; lit. Head of the Month) is a minor holiday observed at the beginning of every month in the Hebrew calendar, marked by the birth of a new moon. Rosh Chodesh is observed for either one or two days, depending on whether the previous month contained 29 or 30 days. Origin The Book of Exodus establishes the new moon of Nisan, which is the first month of Aviv, as the beginning of the Hebrew calendar: In the Book of Numbers, God speaks of the celebration of the new moon to Moses: In , both new and full moon are mentioned as a time of recognition by the Hebrews: In the Bible, Rosh Chodesh is often referred to simply as "Chodesh", as the Hebrew word "chodesh" can mean both "month" and "new month". Declaring the month Judaism uses a lunisolar calendar, so Rosh Chodesh is celebrated in connection with the date of the new moon. Originally, the date of Rosh Chodesh was confirmed on the testimony of witnesses observing the new moon, a procedure known as kiddush hachodesh (sanctification of the month). After the Sanhedrin declared Rosh Chodesh for either a full (30-day) or defective (29-day) month, news of it would then be communicated throughout Israel and the diaspora. This system was dependent on the functioning of the Sanhedrin to declare the month, and to communicate this month to far-flung Jewish communities. In the 4th century CE, this became impossible and instead a fixed calendar of 29- and 30-day months (see Hebrew calendar for details) was instituted by Hillel II. At the end of a 29-day month, Rosh Chodesh is celebrated for one day, on the first day of the new month. At the end of a 30-day month, Rosh Chodesh is celebrated for two days - the 30th day of the previous month, and the 1st day of the new month. Observance Announcement Despite the existence of a fixed calendar, Rosh Chodesh is still announced in synagogues on the preceding Shabbat (called Shabbat Mevarchim — The Shabbat of Blessing [the new month]). The announcement is made after the reading of the sefer torah, before returning it to the aron kodesh. The name of the new month, and the day of the week on which it falls, is given during the prayer. Some communities customarily precede the prayer by