One-Page Learn · The Halachos at a glance
קִדּוּשׁ הַחֹדֶשׁ
Sanctification of the New Month 1
Sefer Zemanim · Lunar months against solar years, the thirty day ceiling on a month, and the court that alone may declare it
11
Days the solar year exceeds the lunar year
13
Months in a full year, when a month is added
30
Days, the longest any lunar month may run
2
Days each month the moon cannot be seen
Part 1Moon months, sun years
- Months by the moon, years by the sun. The months are lunar, from the verse about the burnt offering of the month when it is renewed, and the years are solar, from the charge to keep the month of spring. (1:1)
- Eleven days of drift, one added month. A solar year exceeds a lunar year by roughly eleven days, so when the surplus reaches about 30 days an additional month is added and the year runs to thirteen months, which is called a full year. (1:2)
- Whole months only, never loose days. A year cannot consist of twelve months and an odd number of days, for the Sages read the verse to mean that you count the months of a year and not the days of a year. (1:2)
RememberThe sun and the moon do not agree, and the Torah adds a whole month rather than a handful of days.
Part 2Counting to thirty
- Two dark days, then the sliver. The moon is hidden for about two days each month, roughly one day before its conjunction with the sun and one day after, and the first night it is sighted in the west begins the month. (1:3)
- No month runs past thirty days. Count 29 days from that day: if the moon is sighted on the thirtieth night the thirtieth day is Rosh Chodesh, and if it is not, Rosh Chodesh falls on the thirty first day with no need to sight the moon that night at all. (1:3)
- Chaseir, me'ubar, and the night of fullness. A 29 day month is called chaseir, a 30 day month me'ubar or malei; a moon sighted on the thirtieth night was seen at its appropriate time, and one sighted only on the thirty first is said to have been seen on the night of its fullness. (1:4)
RememberA month may fall short by a day, but it may never be stretched long, whatever the sky is doing.
Part 3Entrusted to the court, and to the Land
- Not like Shabbat. Establishing the month from the sighting is not the province of any individual as Shabbat is, where each person counts six days and rests on the seventh; it is entrusted to the court, and the day the court establishes as Rosh Chodesh is Rosh Chodesh. (1:5)
- A positive commandment to reckon, examine, and announce. It is a Torah commandment for the court to calculate whether the moon will be sighted, to examine the witnesses until the month is sanctified, and to send out word so the people know the day of the festivals. (1:7)
- Only in Eretz Yisrael. The reckoning of months and leap years is done only in the Land; an ordained sage who left for the diaspora may do it solely if no colleague of his stature remained, and if he acts once such a sage has arisen there, his actions are of no consequence. (1:8)
RememberYou may see the new moon with your own eyes and still not have begun the month.