The Calandar and the New Moon
A month is either 29 or 30 days long; in the latter case, the New Moon is celebrated on the 30th day of the month as well as the first day of the next month. The year is usually 12 months long, but in seven out of every 19 years, an additional month of Adar is added; see 427:1. The holidays, and the New Moons of each month, can occur only on certain days of the week (428:1-3).
On the Torah readings that occur just before the holidays see 428:4. On places where the Torah reading should (not) be divided see 428:5-7. On the readings from the Prophets on the Sabbaths from before the Ninth of Av to SUKKOS (Tabernacles) see 428:8. On most Sabbaths, the reading from the Prophets is related to the Torah reading (or if two portions are read from the Torah: to the second one); see 428:8.
It is permitted to do work on the New Moon, but women have the commendable custom of not working then (417:1). It is forbidden to fast on the New Moon, CHANUKAH, or PURIM (418:1-2); on what to do if a public or private fast (including a fast because of a bad dream) coincides with one of those days see 418:2-5. On mourning customs on those days, or on Friday afternoons or on days when TACHANUN is not recited, see 420:1-2. A large meal should be eaten on the New Moon (419:1).
In the evening, morning, and afternoon SHEMONEH ESREH on the New Moon, “May it ascend…” is added in the 17th blessing (as well as in the grace after meals); on what do do if it was omitted see 422:1 and 424:1. After the morning SHEMONEH ESREH, HALLEL (Psalms 113-118, omitting the first parts of 115 and 116) is recited standing, preceded by the blessing “…Who commanded us to read HALLEL” and followed by “They will praise you…”; see 422:2-7. KADDISH is then recited, and four people are called to read Num.28:1-15 from the Torah (423:1-2); customs differ as to whether Num.28:11-15 is also recited by individuals before the morning service (421:1). KADDISH, ASHREI, and U-VA LE-TZION are then recited, the TEFILLIN are removed, and the MUSAF AMIDAH is recited. After the reader’s repetition of that AMIDAH, KADDISH and Psalm 104 are recited (423:3-4).
If the New Moon is on a Sabbath, “May it ascend…” is added in the fifth blessing of the evening, morning, and afternoon AMIDAH. The regular Sabbath portion is then read from one Torah scroll, and Num.28:9-15 from another one. Isaiah 66 is then read, but in some cases, special readings from the Prophets may take precedence over it. In the MUSAF AMIDAH, the fourth blessing mentions both the Sabbath and the New Moon. If the New Moon is on Sunday, the Sabbath reading from the Prophets is 1 Samuel 20:18-42 (425:1-3).
A person who sees the new moon during the first half of the month (but not before the tenth of Av or YOM KIPPUR; see also 607:1) recites the blessing “…Who by His Word created the heavens…”. This blessing is recited standing outdoors at night, if possible after the Sabbath; see 426:1-4.