Kiddush HaChodesh - Chapter Seventeen

All the principles we have explained above were intended so that you will be ready and prepared to know [how] to sight [the moon]. When you desire to know [how to sight the moon on a particular night], calculate the true position of the sun, the true position of the moon, and the position of the head [of the moon's orbit] for the time of the sighting [of the moon].

Afterwards, subtract the position of the sun from the position of the moon. The remainder is referred to as the first longitude.

After having determined the position of the head and the moon's position,1 you will be able to determine the moon's latitude and whether this latitude is northerly or southerly. This figure is referred to as the first latitude. Be careful with regard to [these two symbols,] the first longitude and the first latitude, and have them at hand [for later calculations].

Consider the first longitude:2 If the figure you arrive at is equal to nine degrees or less, know that it will definitely be impossible for the moon to be sighted on that night throughout Eretz Yisrael; no other calculation is necessary.

If the first longitude is more than fifteen degrees, know that the moon will definitely be sighted throughout Eretz Yisrael; no other calculation is necessary.3

If the first longitude is between nine and fifteen degrees, it will be necessary for you to make further calculations to know whether the moon will be sighted or not.

When does the above apply? When the true position of the moon is located [in the area] between the beginning of the constellation of Capricorn and the end of the constellation of Gemini.4 If, however, the position of the moon [is located in the range] between the beginning of the constellation of Cancer and the end of the constellation of Sagittarius, and the first longitude is ten degrees or less,5 know that it will definitely be impossible for the moon to be sighted on that night throughout Eretz Yisrael; no other calculation is necessary.

If the first longitude6 is more than twenty-four degrees, know that the moon will definitely be sighted throughout Eretz Yisrael; no other calculation is necessary.

If the first longitude is between ten and twenty-four degrees, it will be necessary to make further calculations to know whether or not the moon will be sighted.7

These are the [further] calculations [necessary to determine] the sighting of the moon: Consider the constellation in which the moon is located.8 If it is the constellation of Aries, subtract9 59 minutes from the first longitude. If it is the constellation of Taurus, subtract one degree from the longitude.10 If it is the constellation of Gemini, subtract 58 minutes from the longitude.11 If it is the constellation of Cancer, subtract 5212 minutes from the longitude.

If it is the constellation of Leo, subtract 43 minutes from the longitude.13 If it is the constellation of Virgo, subtract 37 minutes from the longitude. If it is the constellation of Libra, subtract 34 minutes from the longitude.

If it is the constellation of Scorpio, subtract 34 minutes from the longitude. If it is the constellation of Sagittarius, subtract 36 minutes from the longitude.14 If it is the constellation of Capricorn, subtract 44 minutes from the longitude.15 If it is the constellation of Aquarius, subtract 53 minutes from the longitude. If it is the constellation of Pisces, subtract 58 minutes from the longitude.16The remainder after these minutes have been subtracted from the longitude is referred to as the second longitude.

Why are these minutes subtracted? Because the true position of the moon is not the place where the moon will actually be sighted [in the sky]. Instead, there is a [small] difference in both longitude and latitude.17 This [difference] is referred to as the sighting adjustment.

The sighting adjustment for the moon's longitude at the hour of the sighting of the moon18 should always be subtracted from the longitude, as we explained.

[The latter point is not necessarily true,] by contrast, with regard to the sighting adjustment for the moon's latitude.19If the moon's latitude is northerly, we subtract the minutes of the sighting adjustment for the moon's latitude from the moon's first latitude.20 If, however, the moon's latitude is southerly, we add the minutes of the sighting adjustment for the moon's latitude to the moon's first latitude.21 The result after the addition or subtraction of these minutes to or from the [moon's] first latitude is referred to as the second latitude.

How many minutes are added or subtracted? If the moon is in the constellation of Aries, 9 minutes.22 If it is in the constellation of Taurus, 10 minutes. If it is in the constellation of Gemini, 16 minutes. If it is in the constellation of Cancer, 27 minutes. If it is in the constellation of Leo, 38 minutes. If it is in the constellation of Virgo, 44 minutes.

If it is in the constellation of Libra, 46 minutes.23 If it is in the constellation of Scorpio, 45 minutes. If it is in the constellation of Sagittarius, 44 minutes. If it is in the constellation of Capricorn, 36 minutes. If it is in the constellation of Aquarius, 2724 minutes. If it is in the constellation of Pisces, 12 minutes.

Since you know the [number of] minutes [for the adjustment] for each constellation, add or subtract them to or from the first latitude, as was explained, and arrive at the second latitude. You already know whether it will be northerly or southerly,25 and you will know the number of degrees and minutes of this second latitude. Prepare this figure and have it at hand.

Afterwards,26 you must set aside [for later use in subtracting or adding] a portion of this second latitude, because the moon fluctuates slightly in its orbit.27 What is the size of the portion you must separate? [This depends on the position of the moon in the celestial sphere.]28

If the moon is located between the beginning of the constellation of Aries and its twentieth degree - and similarly, [when the moon is located] between the beginning of the constellation of Libra and its twentieth degree - separate two fifths of the second latitude.29

If the moon is located between the twentieth degree of the constellation of Aries and the tenth degree of the constellation of Taurus - and similarly, [when the moon is located] between the twentieth degree of the constellation of Libra and the tenth degree of the constellation of Scorpio - separate one third from the second latitude.

If the moon is located between the tenth degree of the constellation of Taurus and its twentieth degree - and similarly, [when the moon is located] between the tenth degree of the constellation of Scorpio and its twentieth degree - separate one fourth from the second latitude.

If the moon is located between the twentieth degree of the constellation of Taurus and its end - and similarly, [if the moon is located] between the twentieth degree of the constellation of Scorpio and its end - separate one fifth from the second latitude.

If the moon is located between the beginning of the constellation of Gemini and its tenth degree - and similarly, [if the moon is located] between the beginning of the constellation of Sagittarius and its tenth degree - separate one sixth of the second latitude.

If the moon is located between the tenth degree of the constellation of Gemini and its twentieth degree - and similarly, [if the moon is located] between the tenth degree of the constellation of Sagittarius and its twentieth degree - separate one twelfth from the second latitude.

If the moon is located between the twentieth degree of the constellation of Gemini and its twenty-fifth degree - and similarly, [if the moon is located] between the twentieth degree of the constellation of Sagittarius and its twenty-fifth degree - separate one twenty-fourth from the second latitude.

If the moon is located between the twenty-fifth degree of the constellation of Gemini and the fifth degree of the constellation of Cancer - and similarly, [if the moon is located] between the twenty-fifth degree of the constellation of Sagittarius and the fifth degree of the constellation of Capricorn - do not make any separation, because at this point the moon does not fluctuate at all from its orbit.30

If the moon is located between the fifth degree of the constellation of Cancer and its tenth degree - and similarly, [if the moon is located] between the fifth degree of the constellation of Capricorn and its tenth degree - separate one twenty-fourth from the second latitude.

If the moon is located between the tenth degree of the constellation of Cancer and its twentieth degree - and similarly, [if the moon is located] between the tenth degree of the constellation of Capricorn and its twentieth degree - separate one twelfth from the second latitude.

If the moon is located between the twentieth degree of the constellation of Cancer and its end - and similarly, [if the moon is located] between the twentieth degree of the constellation of Capricorn and its end - separate one sixth from the second latitude.

If the moon is located between the beginning of the constellation of Leo and its tenth degree - and similarly, [if the moon is located] between the beginning of the constellation of the Aquarius and its tenth degree - separate one fifth of the second latitude.

If the moon is located between the tenth degree of the constellation of Leo and its twentieth degree - and similarly, [if the moon is located] between the tenth degree of the constellation of Aquarius and its twentieth degree - separate one fourth from the second latitude.

If the moon is located between the twentieth degree of the constellation of Leo and the tenth degree of the constellation of Virgo, and similarly, [if the moon is located] between the twentieth degree of the constellation of Aquarius and tenth degree of the constellation of Pisces - separate one third from the second latitude.

If the moon is located between the tenth degree of the constellation of Virgo and its end - and similarly, [if the moon is located] between the tenth degree of the constellation of Pisces and its end - separate two fifths from the second latitude.

This portion that is separated from the second latitude is referred to as the circuit of the moon.

Afterwards, go back and consider whether the latitude of the moon is northerly or southerly. If it is northerly, subtract [the adjustment referred to as] the circuit of the moon from the second longitude.31 If the moon's longitude is southerly, add the circuit of the moon to the second longitude.32

When does the above apply? When the moon's position is located between the beginning of the constellation of Capricorn and the end of the constellation of Gemini.33 If, however, the moon's position is located between the beginning of the constellation of Cancer and the end of the constellation of Sagittarius,34 the opposite is true: If the moon's latitude is northerly, the circuit should be added to the second longitude,35 and if the moon's latitude is southerly, the circuit should be subtracted from the second longitude.36

The remainder after the additions or subtractions have been made to the second longitude is referred to as the third longitude. Know that if there is no fluctuation within the circuit, and there is no figure to be separated from the second latitude,37 the second longitude also will serve as the third longitude, without any decrease or increase.

Afterwards, go back and see the constellation in which the third longitude - i.e., [the amended figure representing] the distance between the sun and the moon - is located:38 If it is located in the constellation of Pisces or Aries, add one sixth [of its length] to the third longitude.39 If the [third] longitude is located in the constellation of Aquarius or the constellation of Taurus, add one fifth [of its length] to the third longitude.40 If the [third] longitude is located in the constellation of Capricorn or the constellation of Gemini, add one sixth [of its length] to the third longitude.

If the [third] longitude is located in the constellation of Sagittarius or the constellation of Cancer, leave the third longitude as it is, without making any addition or subtraction.41 If the [third] longitude is located in the constellation of Scorpio or the constellation of Leo, subtract one fifth [of its length] from the third longitude. If the [third] longitude is located in the constellation of Libra or the constellation of Virgo, subtract one third [of its length] from the third longitude.42

The figure resulting from these subtractions or additions to the third longitude, or from leaving it without adjustment, is referred to as the fourth longitude.

[Afterwards, a further correction is necessary:] Return to the first latitude,43 and set aside two thirds [of its length]. This is called the correction [resulting from geographic] latitude.44

Consider whether the latitude of the moon is northerly. If so, add the correction [resulting from geographic] latitude to the fourth longitude.45 If the latitude of the moon is southerly, subtract the correction [resulting from geographic] latitude from the fourth longitude.46 The figure resulting from these subtractions or additions to the fourth longitude is referred to as the arc of sighting.

What is implied? For example, let us attempt to determine whether or not it will be possible to sight the moon on Friday night, the second of Iyar of this year: First, it is necessary to determine the true position of the sun, the true position of the moon, and the moon's latitude for this time47 according to the methods that were disclosed [in the previous chapters].

The result is that the true position of the sun is seven degrees and nine minutes in the constellation of Taurus, in symbols 7° 9'. The true position of the moon is eighteen degrees and thirty-six minutes in the constellation of Taurus, in symbols 18° 36'. The moon's latitude is three degrees and fifty-three minutes, in symbols 3° 53', and it is southerly. This is the first latitude.

Afterwards, you should subtract the position of the sun from the position of the moon, arriving at a remainder of eleven degrees and twenty-seven minutes, in symbols 11° 27'. This is the first longitude.

Since the moon is located in the constellation of Taurus, the sighting adjustment for the longitude will be one degree. This should be subtracted from the first longitude, producing a second longitude of 10 degrees and twenty-seven minutes, in symbols 10° 27'. The sighting adjustment for the latitude is ten minutes. Since the moon's latitude is southerly, this sighting adjustment of ten minutes should be added to the moon's latitude, producing a second latitude of four degrees and three minutes, in symbols 4° 3'.

Since the moon is located in the eighteenth minute of the constellation of Taurus, it is proper to set aside one fourth of the second latitude as the circuit of the moon. Thus, at this time, the circuit of the moon will be one degree and one minute. We pay no attention to the seconds.

Since the latitude of the moon is southerly and the true position of the moon is located between the beginning [of the constellation] of Capricorn and the beginning [of the constellation] of Cancer, it is correct to add the circuit of the moon to the second longitude. Thus, the third longitude will be eleven degrees and twenty-eight minutes, in symbols 11° 28'.

Since this longitude is located in the constellation of Taurus, it is fitting to add one fifth to the third longitude - i.e., two degrees and eighteen minutes. Thus, the fourth longitude will be thirteen degrees and forty-six minutes, in symbols 13° 46'.

We then go back to the first latitude and separate two thirds of it. Thus, the correction [resulting from geographic] latitude is two degrees and thirty-five minutes. Since the latitude is southerly, the correction [resulting from geographic] latitude should be subtracted from the fourth longitude, leaving a remainder of eleven degrees and eleven minutes, in symbols 11° 11'. This is the arc of sighting on this night.

Following this process, you can determine the number of degrees and the number of minutes every night for the moon's sighting48, which you desire for all time.

After you have determined this arc [of sighting], consider it. Know [these rules]: If the arc of sighting is nine degrees or less, it is impossible for the moon to be sighted anywhere in Eretz Yisrael. If the arc of sighting is more than fourteen degrees, it is impossible49 for it not to be seen and openly revealed throughout Eretz Yisrael.

If the arc of sighting is between the beginning of the tenth degree and the end of the fourteenth degree, [the following procedure should be followed:] One should consider the arc of sighting in relation to the first longitude50 and determine whether or not the moon will be seen from the limits prevalent [at that time]. They are referred to as the sighting limits.

The following are the sighting limits: If the arc of sighting is between nine and ten degrees, or more than ten [degrees], and the first longitude is thirteen degrees or more, [the moon] will surely be sighted. If the arc is less than this, or if the first longitude is less than this, it will not be sighted.

If the arc of sighting is between ten and eleven degrees, or more than eleven [degrees], and the first longitude is twelve degrees or more, [the moon] will surely be sighted. If the arc is less than this, or if the first longitude is less than this, it will not be sighted.

If the arc of sighting is between eleven and twelve degrees, or more than twelve [degrees], and the first longitude is eleven degrees or more, [the moon] will surely be sighted. If the arc is less than this, or if the first longitude is less than this, it will not be sighted.

If the arc of sighting is between twelve and thirteen degrees, or more than thirteen [degrees], and the first longitude is ten degrees or more, [the moon] will surely be sighted. If the arc is less than this, or if the first longitude is less than this, it will not be sighted.

If the arc of sighting is between thirteen and fourteen degrees, or more than fourteen [degrees], and the first longitude is nine degrees or more, [the moon] will surely be sighted. If the arc is less than this, or if the first longitude is less than this, it will not be sighted. This concludes the sighting limits.

What is implied? If we were to consider the arc of sighting for Friday night, the second of Iyar of this year, we would calculate the arc of sighting to be eleven degrees and eleven minutes, as you have already determined.51

Since the arc of sighting is between ten and fourteen degrees, it is necessary to consider it in relation to the first longitude. It has already been established that on this night, the [first] longitude is ten degrees and twenty seven minutes. Since the first longitude is greater than eleven [degrees], we can be assured that the moon will be sighted on that night according to the limits established. Similar procedures should be followed [on every occasion when it is necessary to consider] the arc of sighting in relation to its first longitude.

From all the above, you have seen the extent of the calculations, and the additions and the subtractions that required much effort to present a method that comes close [to being exact]52 without necessitating extremely complicated calculations. [This process is necessary] because the moon has major incongruities in its orbit.

In this vein, our Sages said,53 "'The sun knows the time of its setting'; the moon does not know the time of its setting." Similarly, our Sages said,54 "At times, its setting is prolonged, and at times, it is hastened." This is reflected in these calculations, where at times it is necessary to add, and at times it is necessary to subtract until we arrive at the arc of sighting. And as explained, at times the arc of sighting is great, and at times it is small.

The rationales for all these calculations, and the reasons why this number is added, and why that subtraction is made, and how all these concepts are known, and the proofs for each of these principles are [the subject] of the wisdom of astronomy and geometry, concerning which the Greeks wrote many books.

These texts are presently in the hands of the sages. The texts written by the Sages of Israel in the age of the prophets from the tribe of Yissachar55 have not been transmitted to us. Nevertheless, since these concepts can be proven in an unshakable manner, leaving no room for question, the identity of the author, be he a prophet or a gentile, is of no concern.56 For a matter whose rationale has been revealed and has proven truthful in an unshakable manner, we do not rely on [the personal authority of] the individual who made these statements or taught these concepts, but on the proofs he presented and the reasons he made known.57