NEW MOON -  Hebrew: Rosh Hodesh; "head of the month", the first day or beginning of the month. The Torah placed its celebration on a par with the observance of the festivals, declaring "Also in the day of your gladness, and in your appointed seasons, and in your new moons, ye shall blow with the trumpets over your burnt-offerings..." (Num. 10:10). A special Musaf sacrifice was ordained for the day (Num. 28:11–15). The Bible mentions various practices observed on it, including festive meals (I Sam. 20:18, and Rashi ad loc.), abstention from business transactions (Amos 8:5), and the practice of visiting the prophet (II Kings 4:23). When foretelling the chastisements that will come upon the Jewish people, Hosea says that the joys of the New Moon will cease (Hos. 2:13). The redemption is viewed as a time when "from one new moon to another, and from one Sabbath to another, shall all flesh come to worship before Me saith the Lord" (Isa. 66:23).

Originally, the New Moon was not fixed by astronomical calculations, but was solemnly proclaimed after witnesses had testified to the reappearance of the crescent of the moon. On the 30th of each month, the members of the High Court assembled in a courtyard in Jerusalem, named Beit Ya'azek, where they waited to receive the testimony of two reliable witnesses; they then sanctified the New Moon. If the moon's crescent was not seen on the 30th day, the New Moon was automatically celebrated on the 31st day. To inform the population of the beginning of the month, beacons were kindled on the Mount of Olives and thence over the entire land and in parts of the Diaspora. Later, however, the Samaritans began to light misleading beacons, and the High Court despatched messengers to far-removed communities. Those Jews who lived great distances from Jerusalem always celebrated the 30th day of the month as the New Moon. On those occasions when they were informed of its postponement to the 31st, they also observed this second consecutive day as the New Moon (RH 1:3–2:7). By the middle of the fourth century, the sages had established a permanent calendar and the public proclamation of the New Moon was discontinued. A relic of the original practice is, however, retained in the synagogue custom of announcing the New Moon on the Sabbath preceding its celebration.

Work is permitted on the New Moon (Shab. 24a; Hag. 18a; Ar. 10b), although it was customary for women to abstain from it (TJ, Ta'an. 1:6, 64c). They were allowed to observe this additional semi-festival as a reward for not having surrendered their jewelry for the creation of the golden calf (Tos. to RH 23a, s.v. Mishum). It later became customary for them to refrain from difficult labor, such as weaving, but to do light work such as sewing (Simon b. Zemah Duran, Tashbez, pt. 3no. 244; cf. Rema, OH 417).

The biblical commandment of joy, so basic to festivals, (Deut. 16:14) is not explicitly prescribed in relation to the New Moon. Nevertheless, the rabbis inferred its applicability from the fact that the Bible equated the New Moon with the festivals (Num. 10:10), and from the duty to recite on it "This is the day which the Lord hath made; We will rejoice and be glad in it" (Ps. 118:24; ADPB, 770; Tur, YD, 401). It is therefore forbidden to fast on the New Moon (Ta'an. 2:10), and any funeral service is abbreviated (MK 3:9 and Sh. Ar., OH 420). Conversely, it is meritorious to partake of a festive repast (Sh. Ar., OH 419:1).

The recitation of the half-Hallel on the New Moon goes back to talmudic times (Ta'an. 28b). Parts of the Hallel were omitted since the day was not biblically sanctified by the prohibition of labor (Ar. 10b). There is a difference of opinion among the codifiers as to whether the usual blessing that "who has hallowed us by Thy commandments and has commanded us to read the Hallel" (ADPB, 756) should be recited on Rosh Hodesh. In most communities, the blessing is recited (Isserles and Sh. Ar., OH 422:2), but Shneur Zalman, the founder of Habad Hasidism, ruled that only the cantor is to say the blessing, while the congregation merely responds "Amen."

On the New Moon the special prayer Ya'aleh ve-Yavo is inserted in the Amidah and in the Grace after Meals (Shab. 24a), and Tahanun is not recited. The Torah reading designated for the day describes the New Moon sacrifices (Num. 28:1–15; Meg. 21b–22a). Musaf is also recited since an additional sacrifice was brought on this day; it begins with the words: "The beginnings of the months Thou didst assign unto Thy people for a season of atonement throughout their generations" (ADPB, 778).

The day before the New Moon has achieved importance among kabbalists, who observe it as a day of fast and repentance. It is called Yom Kippur Katan, a minor day of atonement.