One-Page Learn · The Halachos at a glance
קִדּוּשׁ הַחֹדֶשׁ
Sanctification of the New Month 18
Sefer Zemanim · Why a calculated sighting still fails, the tradition from Moses that lets the court establish months it may not sanctify, and the geography that makes an eastern report evidence and a western one worthless
4
Fewest full months that may be established in a year
8
Most full months that may be established in a year
9° 5'
Arc of sighting in the example that puts the court on guard
30-35
Degrees north, the latitudes parallel to Eretz Yisrael
Part 1Why a calculated sighting can still fail
- The calculation yields a probability, not a fact. Even where the reckoning indicates the moon should be sighted on a given night, the sighting is only probable, since it may be covered by clouds, the place may lie in a valley, or a tall mountain in the west may block the view so that the watchers are as though in a valley. (18:1)
- Height and shoreline beat a large crescent. A person in a low place will not sight the moon even when the crescent is large, while a person on a high and lofty mountain will sight it though it is very small, and so will one dwelling on the seashore or travelling on a ship in the Mediterranean. (18:1)
- Clear winter air, smoky summer air. On a clear day in the rainy season the air is clean and the heavens appear more brilliant so the moon is more visible, while in the summer the air is like smoke because of the dust and the moon appears small. (18:2)
- Short limits produce a small moon. Where the arc of sighting and the first longitude are short the crescent is small and can be seen only from a very high altitude, and where they run long past their minimal limits the moon appears larger, its visibility increasing with them. (18:3)
- Two questions the court must ask. The court keeps its attention on the season and the place and asks the witnesses where they were standing; with an arc of sighting of nine degrees and five minutes and a first longitude of exactly thirteen degrees, testimony given in the summer or from a low place is suspected and heavily cross examined, while in the rainy season or a very high place the moon would surely have been sighted unless clouds obscured it. (18:4)
RememberWhere you were standing is not background to the testimony. It is the question the court is instructed to ask out loud.
Part 2Months the court may establish and may not sanctify
- Adding a day each time breaks the year. Where the moon is not sighted on the thirtieth a day is added, but if that were repeated month after month the new month would begin after thirty days throughout the year, and in the last month the moon would be visible on the night of the twenty fifth or twenty sixth, which the Rambam calls the most ludicrous and demeaning situation there could be. (18:5, 18:6)
- The case is common, not theoretical. Months in which the moon goes unsighted at the beginning are very likely and occur often in countries with long rainy seasons and cloudy skies, whether because sighting was impossible or because the crescent was small and nobody was watching for it. (18:7)
- One full, one lacking, from Moses. By a tradition reaching back to Moses, when the moon is not sighted month after month the court establishes one full month of thirty days and one lacking month of twenty nine, sometimes two full or two lacking in succession as the calculations require, establishing these months and deliberately not sanctifying them, since sanctification depends solely on the sighting. (18:8)
- Four at least, eight at most, and a feast even so. The calculations aim at a moon sightable in the following month at its proper time and not before, never fewer than four full months in a year and never more than eight, and a full month established by calculation still receives its celebratory feast. (18:9)
- The rule that never bends. Talmudic passages where the court appears to rely on computation, and the year in which Rabbi declared nine months lacking, all belong to the case where the moon was not sighted at its proper time; when the moon is seen at its proper time, its first shining after conjunction with the sun, it is always sanctified, and in the present era we rely solely on the widespread calculations of the mean. (18:10, 18:11, 18:12)
RememberThey establish these months and they do not sanctify them. The arithmetic can hold the calendar together and it can never do the one thing that makes a month holy.
Part 3West, east, and the only court that counts
- A western sighting proves nothing. If the moon is sighted in Eretz Yisrael it will be sighted in all lands to the west at the same latitude, but it may be sighted there even when the calculations indicate it will not be sighted in Eretz Yisrael, so a sighting in a western country is no indication either way. (18:13)
- A western failure proves a great deal. If the moon was not sighted on the mountains of the countries west of Eretz Yisrael that lie at the same latitude, it surely was not sighted in Eretz Yisrael. (18:14)
- East runs the other way. If the moon was not sighted in Eretz Yisrael it certainly was not sighted in eastern lands at the same latitude, while a sighting in Eretz Yisrael leaves the east uncertain; accordingly a sighting reported from an eastern country establishes that the moon was surely sighted in Eretz Yisrael, and a failure reported from the east establishes nothing. (18:15)
- The band that makes the comparison work. All of this holds only for countries at the same latitude as Eretz Yisrael, thirty to thirty five degrees north of the equator, and does not carry to lands more northerly or less northerly, which are not parallel to it. (18:16)
- Stated to make the Torah great, not to shift the authority. The laws of sighting in eastern and western cities were clarified to make the Torah great and glorious, and not so that people living east or west should depend on their own sighting, which is of no consequence whatsoever; we rely only on the sanctification of the moon performed by the court in Eretz Yisrael. (18:16)
RememberTwo riders arrive the same night with the same word. The one from the east has told the court something and the one from the west has not.