ב"ה

# Rambam - 3 Chapters a Day

## Kiddush HaChodesh - Chapter Fifteen, Kiddush HaChodesh - Chapter Sixteen, Kiddush HaChodesh - Chapter Seventeen

Classes on 3 Chapters Rambam

## Kiddush HaChodesh - Chapter Fifteen

1

If you desire to know the true position of the moon1 on any particular date, first calculate the mean of the moon at the time of the sighting for the desired date. Then calculate the mean of the [moon within its] path and the sun's mean [position] for that date. Subtract the sun's mean from the moon's mean and double the remainder.2 The resulting figure is referred to as the double elongation.

א

אִם תִּרְצֶה לֵידַע מְקוֹם הַיָּרֵח הָאֲמִתִּי בְּכָל יוֹם שֶׁתִּרְצֶה. תּוֹצִיא תְּחִלָּה אֶמְצַע הַיָּרֵחַ לִשְׁעַת הָרְאִיָּה לְאוֹתוֹ הַלַּיְלָה שֶׁתִּרְצֶה. וְכֵן תּוֹצִיא אֶמְצַע הַמַּסְלוּל וְאֶמְצַע הַשֶּׁמֶשׁ לְאוֹתוֹ הָעֵת. וְתִגְרַע אֶמְצַע הַשֶּׁמֶשׁ מֵאֶמְצַע הַיָּרֵחַ. וְהַנִּשְׁאָר תִּכְפּל אוֹתוֹ. וְזֶה הוּא הַנִּקְרָא מֶרְחָק הַכָּפוּל:

2

As mentioned previously, the intent of all the calculations in these chapters is to know how to sight the moon. [In this context, the size of this double elongation is significant.]

[To explain:] It is impossible for this double elongation to be less than five degrees3 or more than 62 degrees4 on the night the moon is to be sighted. Its measure will never exceed or fall short of these numbers.

ב

וּכְבָר הוֹדַעְנוּ שֶׁלֹּא בָּאנוּ בְּכָל אֵלּוּ הַחֶשְׁבּוֹנוֹת שֶׁעָשִׂינוּ בִּפְרָקִים אֵלּוּ אֶלָּא לָדַעַת רְאִיַּת הַיָּרֵחַ. וּלְעוֹלָם אִי אֶפְשָׁר שֶׁיִּהְיֶה מֶרְחָק זֶה הַכָּפוּל בְּלֵיל הָרְאִיָּה שֶׁיִּרְאֶה בָּהּ הַיָּרֵחַ אֶלָּא מֵחָמֵשׁ מַעֲלוֹת עַד ס''ב מַעֲלוֹת. וְאִי אֶפְשָׁר שֶׁיּוֹסִיף עַל זֶה וְלֹא יִגְרַע מִמֶּנּוּ:

3

Accordingly, it is necessary to contemplate [the length of] this double elongation. If the double elongation is five degrees or near that measure, there is no need to be concerned with an increase, and its measure need not be increased. If [the length of] the double elongation is between six and eleven degrees, one should add one degree to the mean of the [the moon] within its path.5

If [the length of] the double elongation is between twelve and eighteen degrees, one should add two degrees to the mean of [the moon] within its path. If [the length of] the double elongation is between nineteen and 24 degrees, one should add three degrees to the mean of [the moon] within its path. If [the length of] the double elongation is between 25 and 31 degrees, one should add four degrees to the mean of [the moon] within its path. If [the length of] the double elongation is between 32 and 38 degrees, one should add five degrees to the mean of [the moon] within its path.

If [the length of] the double elongation is between 39 and 45 degrees, one should add six degrees to the mean of [the moon] within its path. If [the length of] the double elongation is between 46 and 51 degrees, one should add seven degrees to the mean of [the moon] within its path. If [the length of] the double elongation is between 52 and 59 degrees, one should add eight degrees to the mean of [the moon] within its path. If [the length of] the double elongation is between 60 and 63 degrees, one should add nine degrees to the mean of [the moon] within its path.

The mean of [the moon] within its path that results after these additions have been made is referred to as the correct course.

ג

וְהוֹאִיל וְהַדָּבָר כֵּן. הִתְבּוֹנֵן בְּמֶרְחָק זֶה הַכָּפוּל. אִם יִהְיֶה הַמֶּרְחָק הַכָּפוּל חָמֵשׁ מַעֲלוֹת אוֹ קָרוֹב לְחָמֵשׁ אֵין חוֹשְׁשִׁין לְתוֹסֶפֶת וְלֹא תּוֹסִיף כְּלוּם. וְאִם יִהְיֶה הַמֶּרְחָק הַכָּפוּל מִשֵּׁשׁ מַעֲלוֹת עַד אַחַת עֶשְׂרֵה מַעֲלוֹת תּוֹסִיף עַל אֶמְצַע הַמַּסְלוּל מַעֲלָה אַחַת. וְאִם יִהְיֶה מֶרְחָק הַכָּפוּל מִשְּׁתֵּים עֶשְׂרֵה מַעֲלוֹת עַד י''ח מַעֲלוֹת תּוֹסִיף עַל אֶמְצַע הַמַּסְלוּל שְׁתֵּי מַעֲלוֹת. וְאִם יִהְיֶה הַמֶּרְחָק הַכָּפוּל מִי''ט מַעֲלוֹת עַד כ''ד מַעֲלוֹת תּוֹסִיף עַל אֶמְצַע הַמַּסְלוּל שָׁלֹשׁ מַעֲלוֹת. וְאִם יִהְיֶה הַמֶּרְחָק הַכָּפוּל מִכ''ה מַעֲלוֹת עַד ל''א מַעֲלוֹת תּוֹסִיף עַל אֶמְצַע הַמַּסְלוּל ד' מַעֲלוֹת. וְאִם יִהְיֶה הַמֶּרְחָק הַכָּפוּל מִל''ב מַעֲלוֹת עַד ל''ח מַעֲלוֹת תּוֹסִיף עַל אֶמְצַע הַמַּסְלוּל ה' מַעֲלוֹת. וְאִם יִהְיֶה הַמֶּרְחָק הַכָּפוּל מִל''ט מַעֲלוֹת עַד מ''ה מַעֲלוֹת תּוֹסִיף עַל אֶמְצַע הַמַּסְלוּל שֵׁשׁ מַעֲלוֹת. וְאִם יִהְיֶה הַמֶּרְחָק הַכָּפוּל מִמ''ו מַעֲלוֹת עַד נ''א מַעֲלוֹת תּוֹסִיף עַל אֶמְצַע הַמַּסְלוּל שֶׁבַע מַעֲלוֹת. וְאִם יִהְיֶה הַמֶּרְחָק הַכָּפוּל מִנ''ב מַעֲלוֹת עַד נ''ט מַעֲלוֹת תּוֹסִיף עַל אֶמְצַע הַמַּסְלוּל ח' מַעֲלוֹת. וְאִם יִהְיֶה הַמֶּרְחָק הַכָּפוּל מִס' מַעֲלוֹת עַד ס''ג מַעֲלוֹת תּוֹסִיף עַל אֶמְצַע הַמַּסְלוּל ט' מַעֲלוֹת. וּמַה שֶּׁיִּהְיֶה אֶמְצַע הַמַּסְלוּל אַחַר שֶׁתּוֹסִיף עָלָיו מַעֲלוֹת אֵלּוּ הוּא הַנִּקְרָא מַסְלוּל הַנָּכוֹן:

4

After the angular distance of the correct course is calculated,6 [the following procedure should be carried out]: If [the result] is less than 180 degrees, the angle of the course7 should be subtracted8 from the mean of the moon at the time of the sighting. If [the result] is more than 180 degrees, the angle of the course should be added9 to the mean of the moon at the time of the sighting.

The figure that remains after this addition or subtraction is made is the true position of the moon at the time of sighting.

ד

וְאַחַר כָּךְ תִּרְאֶה כַּמָּה מַעֲלוֹת הוּא הַמַּסְלוּל הַנָּכוֹן. אִם הָיָה פָּחוֹת מִק''פ מַעֲלוֹת תִּגְרַע מְנַת הַמַּסְלוּל הַזֶּה הַנָּכוֹן מֵאֶמְצַע הַיָּרֵחַ לִשְׁעַת הָרְאִיָּה. וְאִם הָיָה הַמַּסְלוּל הַנָּכוֹן יוֹתֵר עַל ק''פ מַעֲלוֹת עַד ש''ס תּוֹסִיף מְנַת זֶה הַמַּסְלוּל הַנָּכוֹן עַל אֶמְצַע הַיָּרֵחַ לִשְׁעַת הָרְאִיָּה. וּמַה שֶּׁיִּהְיֶה הָאֶמְצַע אַחַר שֶׁתּוֹסִיף עָלָיו אוֹ תִּגְרַע מִמֶּנּוּ הוּא מְקוֹם הַיָּרֵחַ הָאֲמִתִּי לִשְׁעַת הָרְאִיָּה:

5

Know that if the correct course is an even 180 degrees or 360 degrees, there is no angle of the course. Instead, the mean position of the moon at the time of sighting is the true position of the moon at that time.

ה

וְדַע שֶׁאִם יִהְיֶה הַמַּסְלוּל הַנָּכוֹן ק''פ בְּשָׁוֶה אוֹ ש''ס בְּשָׁוֶה אֵין לוֹ מָנָה. אֶלָּא יִהְיֶה מְקוֹם הַיָּרֵחַ הָאֶמְצָעִי לִשְׁעַת הָרְאִיָּה הוּא מָקוֹם הָאֲמִתִּי:

6

What is the angle of its course? If the correct course is ten degrees, its angle will be 50 minutes. If the correct course is twenty degrees, its angle will be 1 degree and 38 minutes. If it is 30, its angle will be 2 degrees and 24 minutes. If it is 40, its angle will be 3 degrees and 6 minutes.10 If it is 50, its angle will be 3 degrees and 44 minutes. If it is 60, its angle will be 4 degrees and 16 minutes.

If it is 70, its angle will be 4 degrees and 41 minutes. If it is 80, its angle will be 5 degrees. If it is 90, its angle will be 5 degrees and 5 minutes. If it is 100, its angle will be 5 degrees and 8 minutes.11 If it is 110, its angle will be 4 degrees and 59 minutes. If it is 120, its angle will be 4 degrees and 40 minutes.12

If it is 130, its angle will be 4 degrees and 11 minutes. If it is 140, its angle will be 3 degrees and 33 minutes. If it is 150, its angle will be 213 degrees and 48 minutes. If it is 160, its angle will be 1 degree and 56 minutes. If it is 170, its angle will be 59 minutes. If it is an even 180 degrees, [the course] will not have an angle. Instead, as stated above, the moon's mean position will be identical with its true position.

ו

וְכַמָּה הִיא מְנַת הַמַּסְלוּל. אִם יִהְיֶה הַמַּסְלוּל הַנָּכוֹן עֶשֶׂר מַעֲלוֹת תִּהְיֶה מְנָתוֹ נ' חֲלָקִים. וְאִם יִהְיֶה הַמַּסְלוּל הַנָּכוֹן כ' מַעֲלוֹת תִּהְיֶה מְנָתוֹ מַעֲלָה אַחַת וְל''ח חֲלָקִים. וְאִם יִהְיֶה שְׁלֹשִׁים תִּהְיֶה מְנָתוֹ שְׁתֵּי מַעֲלוֹת וְכ''ד חֲלָקִים. וְאִם יִהְיֶה מ' תִּהְיֶה מְנָתוֹ שָׁלֹשׁ מַעֲלוֹת וְשִׁשָּׁה חֲלָקִים. וְאִם יִהְיֶה נ' תִּהְיֶה מְנָתוֹ שָׁלֹשׁ מַעֲלוֹת וּמ''ד חֲלָקִים. וְאִם יִהְיֶה ס' תִּהְיֶה מְנָתוֹ אַרְבַּע מַעֲלוֹת וְט''ז חֲלָקִים. וְאִם יִהְיֶה ע' תִּהְיֶה מְנָתוֹ אַרְבַּע מַעֲלוֹת וּמ''א חֲלָקִים. וְאִם יִהְיֶה פ' תִּהְיֶה מְנָתוֹ חָמֵשׁ מַעֲלוֹת. וְאִם יִהְיֶה צ' תִּהְיֶה מְנָתוֹ חָמֵשׁ מַעֲלוֹת וְה' חֲלָקִים. וְאִם יִהְיֶה ק' תִּהְיֶה מְנָתוֹ ה' מַעֲלוֹת וְח' חֲלָקִים. וְאִם יִהְיֶה ק''י תִּהְיֶה מְנָתוֹ ד' מַעֲלוֹת וְנ''ט חֲלָקִים. וְאִם יִהְיֶה ק''כ תִּהְיֶה מְנָתוֹ ד' מַעֲלוֹת וְכ' חֲלָקִים. וְאִם יִהְיֶה ק''ל תִּהְיֶה מְנָתוֹ ד' מַעֲלוֹת וְי''א חֲלָקִים. וְאִם יִהְיֶה ק''מ תִּהְיֶה מְנָתוֹ ג' מַעֲלוֹת וְל''ג חֲלָקִים. וְאִם יִהְיֶה ק''נ תִּהְיֶה מְנָתוֹ שָׁלֹשׁ מַעֲלוֹת וּמ''ח חֲלָקִים. וְאִם יִהְיֶה ק''ס תִּהְיֶה מְנָתוֹ מַעֲלָה אַחַת וְנ''ו חֲלָקִים. וְאִם יִהְיֶה ק''ע תִּהְיֶה מְנָתוֹ מַעֲלָה אַחַת וְנ''ט חֲלָקִים. וְאִם יִהְיֶה ק''פ בְּשָׁוֶה אֵין לוֹ מָנָה כְּמוֹ שֶׁאָמַרְנוּ אֶלָּא מְקוֹם הַיָּרֵחַ הָאֶמְצָעִי הוּא הַמָּקוֹם הָאֲמִתִּי:

7

If the correct course is more than 180 degrees, you should subtract it from 360 to obtain its angle14, as you did for the course of the sun.15

Similarly, if the correct course includes units as well as tens, you should [calculate the average increase per degree and add the proportionate amount to the lower figure]. The procedure used to calculate the angle of the course for the course of the sun should be used to calculate the angle of the correct course [of the moon].16

ז

וְאִם יִהְיֶה הַמַּסְלוּל הַנָּכוֹן יוֹתֵר עַל ק''פ מַעֲלוֹת. תִּגְרַע אוֹתוֹ מִש''ס וְתֵדַע מְנָתוֹ כְּדֶרֶךְ שֶׁעָשִׂיתָ בְּמַסְלוּל הַשֶּׁמֶשׁ. וְכֵן אִם יִהְיוּ בְּמִנְיַן הַמַּסְלוּל אֲחָדִים עִם הָעֲשָׂרוֹת תִּקַּח מִן הַיּוֹתֵר שֶׁבֵּין שְׁתֵּי הַמָּנוֹת הָאֲחָדִים. כְּדֶרֶךְ שֶׁבֵּאַרְנוּ בְּמַסְלוּל הַשֶּׁמֶשׁ בַּמָּנוֹת שֶׁלּוֹ כָּךְ תַּעֲשֶׂה בַּמַּסְלוּל הַנָּכוֹן בַּמָּנוֹת שֶׁלּוֹ:

8

What is implied? Should we desire to know the true position of the moon on Friday night, the second of Iyar in the present year - the starting point for these calculations - the number of complete days that have passed from the date that is the starting point until the date on which we desire to know the true position of the moon is 29. One should [first] calculate the mean position of the sun for that night; this is 35 degrees, 38 minutes and 33 seconds, in symbols 35° 38' 33".

You should then calculate the mean of the moon at the time of the sighting, which is 53 degrees, 36 minutes and 39 seconds, in symbols 53° 36' 39". Afterwards, calculate the mean of [the moon] within its path for this time, which is 103 degrees, 21 minutes and 46 seconds, in symbols, 103° 21' 46". Then subtract the mean position of the sun from the moon's mean, producing a remainder of 17 degrees, 58 minutes and six seconds. This is the elongation. Doubling this figure produces a double elongation of 35 degrees, 56 minutes and 12 seconds, in symbols 35° 56' 12". Therefore, five degrees should be added to the course, as mentioned. Thus, the correct course will be 10817 degrees and 21 minutes. As mentioned above with regard to the sun,18 the minutes are of no consequence in the calculation of the course.

ח

כֵּיצַד. הֲרֵי שֶׁרָצִינוּ לֵידַע מְקוֹם הַיָּרֵחַ הָאֲמִתִּי בִּתְחִלַּת לֵיל עֶרֶב שַׁבָּת שֶׁיּוֹמוֹ שֵׁנִי לְחֹדֶשׁ אִיָּר מִשָּׁנָה זוֹ שֶׁהִיא שְׁנַת הָעִקָּר. וּמִנְיַן הַיָּמִים הַגְּמוּרִים מִתְּחִלַּת לֵיל הָעִקָּר עַד תְּחִלַּת לַיִל זֶה שֶׁאָנוּ רוֹצִים לֵידַע מְקוֹם הַיָּרֵחַ הָאֲמִתִּי בּוֹ כ''ט יוֹם. תּוֹצִיא אֶמְצַע הַשֶּׁמֶשׁ תְּחִלַּת לַיִל זֶה. יֵצֵא לְךָ אֶמְצָעוֹ ל''ה מַעֲלוֹת וְל''ח חֲלָקִים וְל''ג שְׁנִיּוֹת. סִימָנָם ל''ה ל''ח ל''ג. וְתוֹצִיא אֶמְצַע הַיָּרֵחַ לִשְׁעַת הָרְאִיָּה לְעֵת זוֹ. יֵצֵא לְךָ אֶמְצָעוֹ נ''ג מַעֲלוֹת וְל''ו חֲלָקִים וְל''ט שְׁנִיּוֹת. סִימָנָם נ''ג ל''ו ל''ט. וְתוֹצִיא אֶמְצַע הַמַּסְלוּל לְעֵת זוֹ יֵצֵא לְךָ אֶמְצָעוֹ ק''ג מַעֲלוֹת וְכ''א חֲלָקִים וּמ''ו שְׁנִיּוֹת. סִימָנָם ק''ג כ''א מ''ו. תִּגְרַע אֶמְצַע הַשֶּׁמֶשׁ מֵאֶמְצַע הַיָּרֵחַ יִשָּׁאֵר י''ז מַעֲלוֹת וְנ''ח חֲלָקִים וְשֵׁשׁ שְׁנִיּוֹת. וְזֶה הוּא הַמֶּרְחָק. תִּכְפּל אוֹתוֹ יֵצֵא לְךָ הַמֶּרְחָק הַכָּפוּל ל''ה מַעֲלוֹת וְנ''ו חֲלָקִים וְי''ב שְׁנִיּוֹת. סִימָנָם ל''ה נ''ו י''ב. לְפִיכָךְ תּוֹסִיף עַל אֶמְצַע הַמַּסְלוּל חָמֵשׁ מַעֲלוֹת כְּמוֹ שֶׁהוֹדַעְנוּ וְיֵצֵא לְךָ הַמַּסְלוּל הַנָּכוֹן ק''פ מַעֲלוֹת וְכ''א חֲלָקִים. וְאֵין מַקְפִּידִין עַל הַחֲלָקִים בְּמַסְלוּל כְּדֶרֶךְ שֶׁבֵּאַרְנוּ בַּשֶּׁמֶשׁ:

9

When calculating the angle for a course of 108, the result is 5 degrees and one minute. Since the correct course is less than 180 degrees, this figure should be subtracted from the moon's mean, leaving a remainder of 48 degrees, 3519 minutes and 39 seconds.

The seconds should be rounded off and considered to be a minute. Accordingly, the true position of the moon at this time will be 18 degrees and 36 minutes of the nineteenth degree in the constellation of Taurus, in symbols 18° 36'.

In a similar manner, it is possible for you to calculate the true position of the moon at the time of sighting for any date that you desire from the beginning of this year that was chosen as the starting point until the end of all time.

ט

וּבָאנוּ לַחְקֹר עַל מְנַת זֶה הַמַּסְלוּל הַנָּכוֹן שֶׁהוּא ק''ח נִמְצֵאת מָנָה שֶׁלּוֹ חָמֵשׁ מַעֲלוֹת וְחֵלֶק אֶחָד. וּלְפִי שֶׁהַמַּסְלוּל הַנָּכוֹן הָיָה פָּחוֹת מִק''פ תִּגְרַע הַמָּנָה שֶׁהוּא חָמֵשׁ מַעֲלוֹת וְחֵלֶק אֶחָד מִן אֶמְצַע הַיָּרֵחַ. יִשָּׁאֵר מ''ח מַעֲלוֹת וְל''ג חֲלָקִים וְל''ט שְׁנִיּוֹת. תַּעֲשֶׂה הַשְּׁנִיּוֹת חֵלֶק וְתוֹסִיף עַל הַחֲלָקִים. וְנִמְצָא מְקוֹם הַיָּרֵחַ הָאֲמִתִּי בְּשָׁעָה זוֹ בְּמַזַּל שׁוֹר בְּי''ח מַעֲלוֹת וְל''ו חֲלָקִים מִמַּעֲלַת י''ט. סִימָנָם י''ח ל''ו. וְעַל הַדֶּרֶךְ הַזֶּה תֵּדַע מְקוֹם הַיָּרֵחַ הָאֲמִתִּי בְּכָל עֵת רְאִיָּה שֶׁתִּרְצֶה מִתְּחִלַּת שָׁנָה זוֹ שֶׁהִיא הָעִקָּר עַד סוֹף הָעוֹלָם:

Footnotes
1.

I.e., the location of the moon as it appears in the sky.

2.

The Rambam is following the notion that the Earth does not lie at the center of the moon's orbit. Hence, like the sun, the moon has an apogee and a perigee.

Also of significance here is the fact that, as mentioned in the notes on the previous chapter, the orbit of the moon is moving from east to west at a relatively fast pace, 11 degrees, 12 minutes and 19 seconds per day.

A conjunction refers to the time the sun, the moon, and the Earth are aligned in a straight line. Accordingly, the sun's rays are reflected back without being observed from the Earth, and the moon is therefore not seen in the heavens. At the time of the conjunction, the moon is always at its apogee.

(This can be explained as follows: When the moon is aligned directly between the sun and the Earth, it is at the point in its orbit that is closest to the sun. Therefore, the gravitational pull of the sun draws the moon away from the Earth.)

As the moon continues in its orbit, after the conjunction, it and its apogee move away from the sun in opposite directions. Significantly, the angular distance traveled by the moon and its apogee from the sun is the same.

To explain: The moon's mean is moving at rate of 13 degrees, 10 minutes and 35 seconds per day from west to east. Since the sun is also moving from west to east at the rate of 59 minutes and eight seconds per day, every day the moon will have traveled 12 degrees, 11 minutes and 27 seconds from the sun. Its apogee is moving from east to west at a speed of 11 degrees, 12 minutes and 19 seconds per day. When the sun's mean motion is added to that figure, the same total, 12 degrees, 11 minutes and 27 seconds, is reached. Thus, the double elongation, which is calculated by doubling the angular distance between the moon's mean and the sun's mean, represents the angular distance between the moon's mean and the apogee of its orbit.

(The moon also reaches its apogee when it is full. At this point, the sun, the Earth, and the moon are aligned in a straight line, and the gravitational pull of the sun draws the Earth away from the moon. According to contemporary science, however, these two figures are not alike, and the apogee reached at conjunction is greater than the apogee reached at a full moon.)

3.

At this time, the mean position of the moon will have moved 2 1/2 degrees from the mean position of the sun. Unless it moves that distance, its crescent will be too small to be noticed in the sky. This distance will be covered by the moon in slightly less than five hours. Thus, within five hours of the conjunction of the sun and the moon, it will be possible to sight the new moon.

The commentaries have noted a slight incongruity between the Rambam's statements here and his statements at the beginning of Chapter 17, where he states that the longitude at the night of the sighting of the moon will not be less than nine degrees nor more than twenty-four degrees. There is a difference of approximately seven degrees between these two figures. They attempt to resolve this discrepancy by stating that in this chapter the Rambam is speaking in terms of mean distance, while in Chapter 17 he is speaking in terms of true distance. At times, there can be as great as a seven-degree fluctuation between the two figures (Perush, Ralbach).

4.

At this time, 61 hours will have passed since the time of the conjunction, and the moon will have moved 31 degrees from the sun. Under such circumstances, the crescent of the moon will be large enough to be openly visible to all, and no calculations will be necessary.

5.

The difference between the true position of the moon and its mean position depends on the progress of the moon in its epicycle - i.e., the mean of [the moon] within its path, which is moving at approximately 13 degrees a day from east to west, as stated in the previous chapter. The Rambam is stating that a further adjustment is necessary, depending on the distance between the moon and the sun.

During the first days of the month, as the distance between the sun and the moon increases, the moon's progress in its epicycle will vary from its standard rate of progress. According to the medieval science, this variation depends on the movement of the nekudah hanochachit, the point opposite the center of the moon's orbit. According to modern science, this difference depends on the gravitational pull of the sun and other celestial bodies.

6.

I.e., the progress of the moon in its epicycle.

7.

This refers to the angle between the line extending from the mean position of the moon to the Earth and the line extending from the adjusted position of the moon in its epicycle to the Earth.

8.

When the correct course is less than 180 degrees, the angular distance between the moon's actual position and its mean is less than the mean distance. Hence, a subtraction should be made.

9.

When the correct course is more than 180 degrees, the angular distance between the moon's actual position and its mean is more than the mean distance. Hence, an addition should be made.

10.

The angle of the course of the moon is far larger than the angle of the course of the sun. The rationale for this difference is easily explainable. The moon is far closer to the Earth than the sun. Therefore, the angle between the two lines extending from either end of the course to the Earth will be greater.

11.

The line from the Earth to the moon's mean varies only slightly, while the line from the Earth to the true position of the moon changes to a far greater degree as the moon proceeds along its epicycle, changing the size of the angle of the course. The angle of the course will be largest when the angle between the line extending from the Earth to the true position of the moon and the line extending from the true position of the moon to its mean position is ninety-six degrees - i.e., when these two lines are almost directly perpendicular to each other.

(The reason the largest angle is not at a direct 90-degree angle is that the line to the moon's mean is drawn from the center of the Earth, and the true position takes into consideration the fact that we are looking at the moon from the surface of the Earth, which is removed from its center.)

12.

Our translation is based on the authentic manuscripts and early printings of the Mishneh Torah. The standard printed text reads 4 degrees and 20 minutes.

13.

Here, also, there is a printing error in the standard printed texts of the Mishneh Torah, and those texts read 3 degrees.

14.

For the same angle is produced regardless of whether one makes an increase or a decrease from 180° or 360°.

15.

See Chapter 13, Halachot 5-6.

16.

See Chapter 13, Halachah 7.

17.

In the standard printed texts of the Mishneh Torah, there is a printing error, and those texts read 180 degrees.

18.

See Chapter 13, Halachah 9.

19.

Here also there is a printing error in the standard published text, which reads 33 minutes.

## Kiddush HaChodesh - Chapter Sixteen

1

The orbit in which the moon revolves [intersects] the orbit in which the sun revolves at an angle,1 [so that] a portion of [the moon's orbit] is inclined to the north of the sun's orbit and a portion is inclined south of the sun's orbit.2 There are two points, one opposite the other, at which these orbits intersect.3

When the moon is at one of these points, it is revolving in the same plane as the sun. As the moon departs from these points, it is proceeding either to the north or to the south of the sun.

The point in the moon's [orbit] at which it begins to be inclined to the north of [the plane of] the sun's [orbit] is referred to as the head, while the point [in its orbit] from which it begins to be inclined to the south of [the plane of] the sun's [orbit] is referred to as the tail.*

This head revolves at a uniform pace,4 [proceeding] in opposition to the movement of the sphere of the constellations5 without increase or decrease - i.e., it moves from [the constellation of] Pisces to [the constellation of] Aquarius. It continuously follows [this pattern].

א

הָעֲגֻלָה שֶׁסּוֹבֶבֶת בָּהּ הַיָּרֵחַ תָּמִיד הִיא נוֹטָה מֵעַל הָעֲגֵלָּה שֶׁסּוֹבֶבֶת בָּהּ הַשֶּׁמֶשׁ תָּמִיד. חֶצְיָהּ נוֹטֶה לְצָפוֹן וְחֶצְיָהּ נוֹטֶה לְדָרוֹם. וּשְׁתֵּי נְקֻדּוֹת יֵשׁ בָּהּ זוֹ כְּנֶגֶד זוֹ שֶׁבָּהֶן פּוֹגְעוֹת שְׁתֵּי הָעֲגֻלּוֹת זוֹ בָּזוֹ. לְפִיכָךְ כְּשֶׁיִּהְיֶה הַיָּרֵחַ בְּאַחַת מִשְּׁתֵּיהֶן נִמְצָא סוֹבֵב בְּעִגּוּלָהּ שֶׁל שֶׁמֶשׁ כְּנֶגֶד הַשֶּׁמֶשׁ בְּשָׁוֶה. וְאִם יֵצֵא הַיָּרֵחַ מֵאַחַת מִשְּׁתֵּי הַנְּקֻדּוֹת נִמְצָא מְהַלֵּךְ לִצְפוֹן הַשֶּׁמֶשׁ אוֹ לִדְרוֹמָהּ. הַנְּקֻדָּה שֶׁמִּמֶּנָּה יַתְחִיל הַיָּרֵחַ לִנְטוֹת לִצְפוֹן הַשֶּׁמֶשׁ הִיא הַנִּקְרֵאת רֹאשׁ. וְהַנְּקֻדָּה שֶׁמִּמֶּנָּה יַתְחִיל הַיָּרֵחַ לִנְטוֹת לִדְרוֹם הַשֶּׁמֶשׁ הִיא הַנִּקְרֵאת זָנָב. וּמַהֲלָךְ שָׁוֶה יֵשׁ לְזֶה הָרֹאשׁ שֶׁאֵין בּוֹ לֹא תּוֹסֶפֶת וְלֹא גֵּרָעוֹן. וְהוּא הוֹלֵךְ בַּמַּזָּלוֹת אֲחוֹרַנִּית מִטָּלֶה לְדָגִים וּמִדָּגִים לִדְלִי וְכֵן הוּא סוֹבֵב תָּמִיד:

2

The mean movement of the head in one day is 3 minutes and 11 seconds.6 Thus, its movement in ten days is 31 minutes and 47 seconds; its movement in one hundred days is 5 degrees, 17 minutes, and 43 seconds, in symbols 5° 17' 43". In one thousand days, its movement is 52 degrees, 57 minutes and 10 seconds, in symbols 52° 57' 10". The remainder [of the sum] of its progress in ten thousand days is 169 degrees, 31 minutes and 40 seconds, in symbols 169° 31' 40".

Thus, the distance it travels in twenty-nine days is 1 degree, 32 minutes and 9 seconds, in symbols 1° 32' 9". Its progress in a regular year is 18 degrees, 44 minutes and 42 seconds, in symbols 18° 44' 42". The mean position of the head on Thursday night [of the present year,] the starting point for these calculations, is 180 degrees, 57 minutes, and 28 seconds, in symbols 180° 57' 28".7

ב

מַהֲלַךְ הָרֹאשׁ הָאֶמְצָעִי בְּיוֹם אֶחָד ג' חֲלָקִים וְי''א שְׁנִיּוֹת. נִמְצָא מַהֲלָכוֹ בְּי' יָמִים ל''א חֲלָקִים וּמ''ז שְׁנִיּוֹת. וְנִמְצָא מַהֲלָכוֹ בְּק' יוֹם ה' מַעֲלוֹת וְי''ז חֲלָקִים וּמ''ג שְׁנִיּוֹת. סִימָנָם הי''ז מ''ג. וְנִמְצָא מַהֲלָכוֹ בְּאֶלֶף יוֹם נ''ב מַעֲלוֹת וְנ''ז חֲלָקִים וְי' שְׁנִיּוֹת. סִימָנָם נ''ב נז''י. וְנִמְצָא שְׁאֵרִית מַהֲלָכוֹ בַּעֲשֶׂרֶת אֲלָפִים יוֹם קס''ט מַעֲלוֹת וְל''א חֲלָקִים וּמ' שְׁנִיּוֹת. סִימָנָם קס''ט לא''מ. וְנִמְצָא מַהֲלָכוֹ לְכ''ט יוֹם מַעֲלָה אַחַת וְל''ב חֲלָקִים וְט' שְׁנִיּוֹת. סִימָנָם א' לב''ט. וְנִמְצָא מַהֲלָכוֹ לְשָׁנָה סְדוּרָה י''ח מַעֲלוֹת וּמ''ד חֲלָקִים וּמ''ב שְׁנִיּוֹת. סִימָנָם י''ח מ''ד מ''ב. וְאֶמְצַע הָרֹאשׁ בִּתְחִלַּת לֵיל ה' שֶׁהוּא הָעִקָּר הָיָה ק''פ מַעֲלוֹת וְנ''ז חֲלָקִים וְכ''ח שְׁנִיּוֹת. סִימָנָם ק''פ נ''ז כ''ח:

3

If you desire to calculate the position of the head at any given date, [you should follow this procedure:] First, calculate the mean progress of the head as you calculated the mean of the sun and the mean of the moon. [Afterwards,] subtract this mean from 360 degrees,8 and the remainder will be the location of the head at that time. The tail's position will always be the [place in the moon's orbit] directly opposite it.

ג

אִם תִּרְצֶה לֵידַע מְקוֹם הָרֹאשׁ בְּכָל עֵת שֶׁתִּרְצֶה. תּוֹצִיא אֶמְצָעָם לְאוֹתוֹ הָעֵת כְּדֶרֶךְ שֶׁתּוֹצִיא אֶמְצַע הַשֶּׁמֶשׁ וְאֶמְצַע הַיָּרֵחַ. וְתִגְרַע הָאֶמְצַע מִש''ס מַעֲלוֹת. וְהַנִּשְׁאָר הוּא מְקוֹם הָרֹאשׁ בְּאוֹתָהּ הָעֵת. וּכְנֶגְדּוֹ לְעוֹלָם יִהְיֶה מְקוֹם הַזָּנָב:

4

What is implied? Let us suppose that we desired to know the location of the head on Friday night, the second of Iyar of this year - the starting point for these calculations. There are 29 complete days between the night of the starting point and the date for which we desire to know the location of the head.

ד

כֵּיצַד. הֲרֵי שֶׁרָצִינוּ לֵידַע מְקוֹם הָרֹאשׁ לִתְחִלַּת לֵיל עֶרֶב שַׁבָּת שֶׁיּוֹמוֹ שֵׁנִי לְחֹדֶשׁ אִיָּר מִשָּׁנָה זוֹ שֶׁהִיא שְׁנַת הָעִקָּר. וּמִנְיַן הַיָּמִים הַגְּמוּרִים מִתְּחִלַּת לֵיל הָעִקָּר עַד תְּחִלַּת לַיִל זוֹ שֶׁאָנוּ רוֹצִים לֵידַע מְקוֹם הָרֹאשׁ בּוֹ כ''ט יוֹם:

5

We should then calculate the mean of the head according to the familiar manner, adding its distance traveled in 29 days to the starting point. Thus, the mean of the head is 182 degrees, 29 minutes and 37 seconds, in symbols 182° 29' 37". This mean should be subtracted from 360, leaving a remainder of 177 degrees, 30 minutes and 23 seconds, in symbols 177° 30' 23".

This is the location of the head. The seconds are of no consequence. Thus, the position of the head will be 27 degrees and 30 minutes within the constellation of Virgo. The position of the tail will be [directly] opposite it: 27 degrees and 30 minutes within the constellation of Pisces.

ה

תּוֹצִיא אֶמְצַע הָרֹאשׁ לָעֵת הַזֹּאת עַל הַדֶּרֶךְ שֶׁיָּדַעְתָּ. וְהוּא שֶׁתּוֹסִיף מַהֲלָכוֹ לְכ''ט יוֹם עַל הָעִקָּר. יֵצֵא לְךָ אֶמְצַע הָרֹאשׁ קפ''ב מַעֲלוֹת וְכ''ט חֲלָקִים וְל''ז שְׁנִיּוֹת. סִימָנָם קפ''ב כ''ט ל''ז. תִּגְרַע אֶמְצַע זֶה מִש''ס יִשָּׁאֵר לְךָ קע''ז מַעֲלוֹת וְל' חֲלָקִים וְכ''ג שְׁנִיּוֹת. סִימָנָם קע''ז לִכְ''ג. וְזֶה הוּא מְקוֹם הָרֹאשׁ. וְאַל תִּפְנֶה אֶל הַשְּׁנִיּוֹת. נִמְצָא מְקוֹם הָרֹאשׁ בְּמַזַּל בְּתוּלָה בְּכ''ז מַעֲלוֹת וְל' חֲלָקִים. וּמְקוֹם הַזָּנָב כְּנֶגְדּוֹ בְּמַזַּל דָּגִים בְּכ''ז מַעֲלוֹת וּשְׁלֹשִׁים חֲלָקִים:

6

There will always be an even half of the celestial sphere between the position of the head and the position of the tail. Therefore, whenever the head is in a particular constellation, the tail will be seven constellations further in the order of constellations, at the same position with regard to degrees and minutes. For example, if the head is ten degrees within a particular constellation, the tail will be ten degrees within the seventh constellation from it.

ו

לְעוֹלָם יִהְיֶה בֵּין הָרֹאשׁ וּבֵין הַזָּנָב חֲצִי הַגַּלְגַּל בְּשָׁוֶה. לְפִיכָךְ כָּל מַזָּל שֶׁתִּמְצָא בּוֹ מְקוֹם הָרֹאשׁ יִהְיֶה הַזָּנָב בְּמַזַּל ז' מִמֶּנּוּ בִּכְמוֹ מִנְיַן הַמַּעֲלוֹת וְהַחֲלָקִים בְּשָׁוֶה. אִם יִהְיֶה הָרֹאשׁ בְּי' מַעֲלוֹת בְּמַזַּל פְּלוֹנִי יִהְיֶה הַזָּנָב בְּי' מַעֲלוֹת מִמַּזַּל ז' מִמֶּנּוּ:

7

After having established the position of the head, the position of the tail, and the true position of the moon, consider [these three figures]: If the position of the moon is the same, both in degrees and in minutes, as its head or tail, then the moon will not be inclined to the north or the south.9

If the position of the moon has passed10 the head11 and it is proceeding in the direction of the tail, know that the moon will be inclined to the north of the [plane] of the sun's [orbit]. If the position of the moon is before the tail12 and it is proceeding in the direction of the head, know that the moon will be inclined to the south of the [plane] of the sun's [orbit].

ז

וּמֵאַחַר שֶׁתֵּדַע מְקוֹם הָרֹאשׁ וּמְקוֹם הַזָּנָב וּמְקוֹם הַיָּרֵחַ הָאֲמִתִּי. הִתְבּוֹנֵן בִּשְׁלָשְׁתָּן. אִם מָצָאתָ הַיָּרֵחַ עִם הָרֹאשׁ אוֹ עִם הַזָּנָב בְּמַעֲלָה אַחַת בְּחֵלֶק אֶחָד. תֵּדַע שֶׁאֵין הַיָּרֵחַ נוֹטֶה לֹא לִצְפוֹן הַשֶּׁמֶשׁ וְלֹא לִדְרוֹמָהּ. וְאִם רָאִיתָ מְקוֹם הַיָּרֵחַ לִפְנֵי מְקוֹם הָרֹאשׁ וְהוּא הוֹלֵךְ כְּנֶגֶד הַזָּנָב. תֵּדַע שֶׁהַיָּרֵחַ נוֹטֶה לִצְפוֹן הַשֶּׁמֶשׁ. וְאִם הָיָה הַיָּרֵחַ לִפְנֵי מְקוֹם הַזָּנָב וַהֲרֵי הוּא הוֹלֵךְ כְּנֶגֶד הָרֹאשׁ. תֵּדַע שֶׁהַיָּרֵחַ נוֹטֶה לִדְרוֹם הַשֶּׁמֶשׁ:

8

The inclination of the moon to the north or to the south is referred to as the moon's latitude.13 If the moon's incline is northerly, it is referred to as a northerly latitude. If the moon's incline is southerly, it is referred to as a southerly latitude. If the moon is positioned at either [the head or the tail], it has no latitude, as explained above.

ח

הַנְּטִיָּה שֶׁנּוֹטֶה הַיָּרֵחַ לִצְפוֹן הַשֶּׁמֶשׁ אוֹ לִדְרוֹמָהּ. הִיא הַנִּקְרֵאת רֹחַב הַיָּרֵחַ. וְאִם הָיָה נוֹטֶה לַצָּפוֹן נִקְרָא רֹחַב צְפוֹנִי. וְאִם הָיָה נוֹטֶה לַדָּרוֹם נִקְרָא רֹחַב דְּרוֹמִי. וְאִם הָיָה הַיָּרֵחַ בְּאַחַת מִשְּׁתֵּי הַנְּקֻדּוֹת לֹא יִהְיֶה לוֹ רֹחַב כְּמוֹ שֶׁבֵּאַרְנוּ:

9

The moon's latitude14 will never exceed five degrees, whether to the north or to the south. This is the pattern it follows. [The moon] begins at the head and diverges slightly [from the sun's orbit, as it proceeds on its own orbit]. [The size of] this divergence continues to increase until it reaches five degrees.15 At this point, [the moon] begins to come slightly closer [to the sun's orbit], until it has no latitude at all when it reaches its tail.

[After it reaches the tail, the moon] will again begin to diverge slightly [from the sun's orbit], until this divergence reaches five degrees. It will then begin to approach [the sun's orbit], until ultimately it has no latitude at all.

ט

לְעוֹלָם לֹא יִהְיֶה רֹחַב הַיָּרֵחַ יֶתֶר עַל ה' מַעֲלוֹת בֵּין בַּצָּפוֹן בֵּין בַּדָּרוֹם. אֶלָּא כָּךְ הוּא דַּרְכּוֹ יַתְחִיל מִן הָרֹאשׁ וְיִתְרַחֵק מִמֶּנּוּ מְעַט מְעַט. וְהַמֶּרְחָק הוֹלֵךְ וְנוֹסָף עַד שֶׁיַּגִּיעַ לְחָמֵשׁ מַעֲלוֹת. וְיַחֲזֹר וְיִתְקָרֵב מְעַט מְעַט עַד שֶׁלֹּא יִהְיֶה לוֹ רֹחַב כְּשֶׁיַּגִּיעַ לַזָּנָב. וְיַחֲזֹר וְיִתְרַחֵק מְעַט מְעַט וְהַמֶּרְחָק נוֹסָף עַד שֶׁיַּגִּיעַ לְחָמֵשׁ מַעֲלוֹת. וְיַחֲזֹר וְיִתְקָרֵב עַד שֶׁלֹּא יִהְיֶה לוֹ רֹחַב:

10

[The following procedure should be applied] if you desire to determine the latitude of the moon, and to [know] whether it is northerly or southerly: First, calculate the position of the head and the true position of the moon at the desired date. Then subtract the position of the head from the true position of the moon. The remainder is referred to as "the course of the latitude."16

If the course of the latitude is between one degree and 180 degrees, the latitude of the moon is northerly. If course of the latitude is more than 180 degrees, the latitude of the moon is southerly. If [the course] is an even 180 degrees or an even 360 degrees, the moon does not have any latitude at all.

Afterwards, determine the size of the angle of the course of the latitude17 - i.e., the extent to which the moon is inclined to the north or to the south. This figure is referred to as the moon's southerly latitude or northerly [latitude], as we explained.

י

אִם תִּרְצֶה לֵידַע רֹחַב הַיָּרֵחַ כַּמָּה הוּא בְּכָל עֵת שֶׁתִּרְצֶה. וְאִם צְפוֹנִי הוּא אוֹ דְּרוֹמִי. תּוֹצִיא מְקוֹם הָרֹאשׁ וּמְקוֹם הַיָּרֵחַ הָאֲמִתִּי לְאוֹתָהּ הָעֵת. וְתִגְרַע מְקוֹם הָרֹאשׁ מִמְּקוֹם הַיָּרֵחַ הָאֲמִתִּי. וְהַנִּשְׁאָר הוּא הַנִּקְרָא מַסְלוּל הָרֹחַב. וְאִם יִהְיֶה מַסְלוּל הָרֹחַב מִמַּעֲלָה אַחַת עַד ק''פ. תֵּדַע שֶׁרֹחַב הַיָּרֵחַ צְפוֹנִי. וְאִם הָיָה הַמַּסְלוּל יֶתֶר עַל ק''פ תֵּדַע שֶׁרֹחַב הַיָּרֵחַ דְּרוֹמִי. וְאִם הָיָה ק''פ בְּשָׁוֶה אוֹ ש''ס בְּשָׁוֶה אֵין לַיָּרֵחַ רֹחַב כְּלָל. וְתַחֲזֹר וְתִרְאֶה מְנַת מַסְלוּל הָרֹחַב כַּמָּה הִיא. וְהוּא שִׁעוּר נְטִיָּתוֹ לַצָּפוֹן אוֹ לַדָּרוֹם. וְהוּא הַנִּקְרָא רֹחַב הַיָּרֵחַ הַדְּרוֹמִי אוֹ הַצְּפוֹנִי כְּמוֹ שֶׁבֵּאַרְנוּ:

11

How large is the angle of the course of the latitude? If the course of the latitude is ten degrees, its angle will be 52 minutes. If the course is twenty degrees, its angle will be one degree and 43 minutes. If the course is thirty degrees, its angle will be 2 degrees and 30 minutes.

If the course is forty degrees, its angle will be 3 degrees and 13 minutes. If the course is fifty degrees, its angle will be 3 degrees and 50 minutes. If the course is sixty degrees, its angle will be 4 degrees and 20 minutes. If the course is seventy degrees, its angle will be 4 degrees and 42 minutes. If the course is eighty degrees, its angle will be 4 degrees and 55 minutes. If the course is ninety degrees, its angle will be 5 degrees.18

יא

וְכַמָּה הִיא מְנַת מַסְלוּל הָרֹחַב. אִם יִהְיֶה מַסְלוּל הָרֹחַב עֶשֶׂר מַעֲלוֹת תִּהְיֶה מְנָתוֹ נ''ב חֲלָקִים. וְאִם יִהְיֶה הַמַּסְלוּל הַזֶּה כ' מַעֲלוֹת תִּהְיֶה מְנָתוֹ מַעֲלָה אַחַת וּמ''ג חֲלָקִים. וְאִם יִהְיֶה הַמַּסְלוּל ל' תִּהְיֶה מְנָתוֹ שְׁתֵּי מַעֲלוֹת וְל' חֲלָקִים. וְאִם יִהְיֶה הַמַּסְלוּל מ' תִּהְיֶה מְנָתוֹ שָׁלֹשׁ מַעֲלוֹת וְי''ג חֲלָקִים. וְאִם יִהְיֶה הַמַּסְלוּל נ' מַעֲלוֹת תִּהְיֶה מְנָתוֹ שָׁלֹשׁ מַעֲלוֹת וְנ' חֲלָקִים. וְאִם יִהְיֶה הַמַּסְלוּל ס' תִּהְיֶה מְנָתוֹ אַרְבַּע מַעֲלוֹת וְכ' חֲלָקִים. וְאִם יִהְיֶה הַמַּסְלוּל ע' תִּהְיֶה מְנָתוֹ ד' מַעֲלוֹת וּמ''ב חֲלָקִים. וְאִם יִהְיֶה הַמַּסְלוּל פ' תִּהְיֶה מְנָתוֹ ד' מַעֲלוֹת וְנ''ה חֲלָקִים. וְאִם יִהְיֶה הַמַּסְלוּל צ' תִּהְיֶה מְנָתוֹ ה' מַעֲלוֹת:

12

If [the course of the latitude] has both units and tens, you should [calculate the average increase per degree and add the proportionate amount to the lower figure], as was done with regard to the course of the sun and the course of the moon.19

What is implied? When the course of the latitude is 53 degrees, [the size of the angle should be determined as follows]. It has already been established that when the course is 50 degrees, its angle is 3 degrees and 50 minutes. When the course is 60 degrees, its angle is 4 degrees and 20 minutes. Therefore, there is a difference of 30 minutes between them, 3 minutes for each degree. Accordingly, [when] calculating the angle for a course of 53 degrees, [the result] will be 3 degrees and 59 minutes. A similar process should be followed with regard to all other figures.

יב

וְאִם יִהְיוּ אֲחָדִים עִם הָעֲשָׂרוֹת תִּקַּח הָרָאוּי לָהֶם לְפִי הַיֶּתֶר שֶׁבֵּין שְׁתֵּי הַמָּנוֹת כְּמוֹ שֶׁעָשִׂיתָ בְּמַסְלוּל הַשֶּׁמֶשׁ וּבְמַסְלוּל הַיָּרֵחַ. כֵּיצַד. הֲרֵי שֶׁהָיָה מַסְלוּל הָרֹחַב נ''ג מַעֲלוֹת. וּכְבָר יָדַעְתָּ שֶׁאִלּוּ הָיָה הַמַּסְלוּל נ' הָיְתָה מְנָתוֹ שָׁלֹשׁ מַעֲלוֹת וְנ' חֲלָקִים. וְאִלּוּ הָיָה הַמַּסְלוּל ס' הָיְתָה מְנָתוֹ ד' מַעֲלוֹת וְכ' חֲלָקִים. נִמְצָא הַיֶּתֶר בֵּין שְׁתֵּי הַמָּנוֹת ל' חֲלָקִים ג' חֲלָקִים לְכָל מַעֲלָה. וְנִמְצָא לְפִי חֶשְׁבּוֹן מַסְלוּל זֶה שֶׁהוּא נ''ג שָׁלֹשׁ מַעֲלוֹת וְנ''ט חֲלָקִים. וְעַל דֶּרֶךְ זוֹ תַּעֲשֶׂה בְּכָל מִנְיָן וּמִנְיָן:

13

Since you know the angles for all the values of the course of the latitude until ninety degrees, as was mentioned, you will be able to know the angle for all possible values of the course. For if the course is between 90 and 180 degrees, subtract the course from 180 and find the angle for the remainder.20

יג

מֵאַחַר שֶׁתֵּדַע מְנָתוֹ שֶׁל מַסְלוּל הָרֹחַב עַד צ' כְּמוֹ שֶׁהוֹדַעְנוּךָ. תֵּדַע מָנוֹת שֶׁל כָּל מִנְיְנוֹת הַמַּסְלוּל. שֶׁאִם יִהְיֶה הַמַּסְלוּל יֶתֶר עַל צ' עַד ק''פ תִּגְרַע הַמַּסְלוּל מִק''פ וְהַנִּשְׁאָר תֵּדַע בּוֹ הַמָּנָה:

14

21Similarly, if the course is between 180 and 270 degrees,22 subtract 180 from [the course] and find the angle for the remainder.23

יד

וְזֶה הוּא רֹחַב הַיָּרֵחַ בִּתְחִלַּת לַיִל זֶה. וְהוּא דְּרוֹמִי שֶׁהֲרֵי הַמַּסְלוּל יֶתֶר עַל ק''פ. וְכֵן אִם הָיָה הַמַּסְלוּל יֶתֶר מִק''פ עַד ר''ע תִּגְרַע מִמֶּנּוּ ק''פ וְהַנִּשְׁאָר תֵּדַע בּוֹ הַמָּנָה:

15

Similarly, if the course is between 270 and 360 degrees, subtract [the course] from 360 and find the angle for the remainder.24

טו

וְאִם הָיָה הַמַּסְלוּל יֶתֶר עַל ר''ע עַד ש''ס. תִּגְרַע אוֹתוֹ מִש''ס וְהַנִּשְׁאָר תֵּדַע בּוֹ הַמָּנָה:

16

What is implied? If the course is 150°, subtract 150 from 180, leaving 30. As mentioned previously, the angle [of a course] of 30 [degrees] will be 2 degrees and 30 minutes. Thus, the angle [of a course] of 150 [degrees] also will be 2 degrees and 30 minutes.

טז

כֵּיצַד. הֲרֵי שֶׁהָיָה הַמַּסְלוּל ק''נ תִּגְרַע אוֹתוֹ מִק''פ נִשְׁאָר ל'. וּכְבָר יָדַעְתָּ שֶׁמְּנַת שְׁלֹשִׁים שְׁתֵּי מַעֲלוֹת וּשְׁלֹשִׁים חֲלָקִים וְכָךְ תִּהְיֶה מְנַת ק''נ שְׁתֵּי מַעֲלוֹת וּשְׁלֹשִׁים חֲלָקִים:

17

If the course is 200°, subtract 180 from 200, leaving 20. As mentioned previously, the angle [of a course] of 20 [degrees] will be 1 degree and 43 minutes. Thus, the angle [of a course] of 200 [degrees] also will be 1 degree and 43 minutes.

יז

הֲרֵי שֶׁהָיָה הַמַּסְלוּל ר'. תִּגְרַע מִמֶּנּוּ ק''פ יִשָּׁאֵר כ'. וּכְבָר יָדַעְתָּ שֶׁמְּנַת כ' הִיא מַעֲלָה אַחַת וּמ''ג חֲלָקִים. וְכֵן אִם תִּהְיֶה מְנַת ר' תִּהְיֶה מַעֲלָה אַחַת וּמ''ג חֲלָקִים:

18

If the course is 300°, subtract 300 from 360, leaving 60. As mentioned previously, the angle [of a course] of 60 [degrees] will be 4 degrees and 20 minutes. Thus, the angle [of a course] of 300 [degrees] also will be 4 degrees and 20 minutes. A similar process should be followed with regard to all other values.

יח

הֲרֵי שֶׁהָיָה הַמַּסְלוּל ש' תִּגְרַע אוֹתוֹ מִש''ס נִשְׁאַר ס'. וּכְבָר יָדַעְתָּ שֶׁמְּנַת שִׁשִּׁים אַרְבַּע מַעֲלוֹת וְכ' חֲלָקִים. וְכָךְ הִיא מְנַת ש' ד' מַעֲלוֹת וְכ' חֲלָקִים. וְעַל דֶּרֶךְ זוֹ בְּכָל הַמִּנְיָנוֹת:

19

[The following procedure should be applied] if one desires to know the latitude of the moon and whether it is either northerly or southerly at the beginning of Friday night, the second of Iyar of this year: It has already been established that the true position of the moon on this night is 18 degrees and 36 minutes within the constellation of Taurus, in symbols 18° 36". [Similarly, it has been established that] the position of the head at that time is 27 degrees and 30 minutes within the constellation of Virgo, in symbols 27° 30'.

[To arrive at the latitude,] you must subtract the position of the head from the position of the moon, leaving a course of the latitude of 231 degrees and 6 minutes, in symbols 231° 6'. [As mentioned,] the minutes are of no consequence with regard to the course. Therefore, according to the principles explained in this chapter, the angle of this course will be 3 degrees and 53 minutes. This is the latitude of the moon at the beginning of this night. It is southerly, for the course is larger than 180 degrees.

יט

הֲרֵי שֶׁרָצִינוּ לֵידַע רֹחַב הַיָּרֵחַ כַּמָּה הוּא וּבְאֵיזוֹ רוּחַ הוּא אִם צְפוֹנִי אוֹ דְּרוֹמִי בִּתְחִלַּת לֵיל עֶרֶב שַׁבָּת שֵׁנִי לְחֹדֶשׁ אִיָּר מִשָּׁנָה זוֹ. וּכְבָר יָדַעְתָּ שֶׁמְּקוֹם הַיָּרֵחַ הָאֲמִתִּי הָיָה בְּלַיִל זֶה בְּי''ח מַעֲלוֹת וְל''ו חֲלָקִים מִמַּזַּל שׁוֹר. סִימָנוֹ י''ח ל''ו. וּמְקוֹם הָרֹאשׁ הָיָה בְּאוֹתָהּ הָעֵת בְּכ''ז מַעֲלוֹת וְל' חֲלָקִים מִמַּזַּל בְּתוּלָה. סִימָנוֹ כז''ל. תִּגְרַע מְקוֹם הָרֹאשׁ מִמְּקוֹם הַיָּרֵחַ. יֵצֵא לְךָ מַסְלוּל הָרֹחַב רל''א מַעֲלוֹת ו' חֲלָקִים. סִימָנוֹ רל''א ו'. לְפִי שֶׁאֵין מַשְׁגִּיחִין עַל הַחֲלָקִים בְּכָל הַמַּסְלוּל. וְנִמְצֵאת הַמָּנָה שֶׁל מַסְלוּל זֶה בַּדְּרָכִים שֶׁבֵּאַרְנוּ בְּפֶרֶק זֶה שָׁלֹשׁ מַעֲלוֹת וְנ''ג חֲלָקִים. וְזֶהוּ רֹחַב הַיָּרֵחַ בִּתְחִלַּת לַיִל זֶה. וְהוּא דְּרוֹמִי שֶׁהֲרֵי הַמַּסְלוּל יֶתֶר עַל ק''פ:

Footnotes
1.

More specifically, as mentioned in Halachah 9, the maximum angular distance between the two orbits is 5 degrees.

2.

The importance of the concept the Rambam introduces here, the difference in latitude between the planes of the orbits of the sun and the moon, becomes significant in the following chapter.

To explain briefly: In the previous chapters, it was explained that the visibility of the moon depends upon the distance in longitude between it and the sun. At the time of conjunction, the sun and the moon are at the same longitudinal point. Therefore, they set at the same time. As the difference in longitude between them increases, the crescent of the moon grows and the time of its setting becomes later, increasing the chances of its visibility.

Nevertheless, the moon's latitude also affects its visibility. The greater the latitude of the moon [i.e., its inclination from the orbit of the sun] the larger its crescent will appear. Also, a northerly latitude causes the moon to set later and thus makes it easier to be sighted. A southerly latitude, by contrast, causes the moon to set earlier and thus makes sighting it more difficult.

3.

The difference in latitude between the orbits of the sun and the moon explains why there is not a lunar eclipse at every full moon, and why there is not a solar eclipse at every conjunction - although at the time of the full moon, the sun, the earth and the moon are aligned in a single line, and at the time of conjunction, the sun, the moon and the earth are aligned in a single line.

Although the longitude of the sun and the moon is the same at these times, since their latitudes are different, the moon's shadow does not interfere with the light of the sun at a conjunction, and the earth's shadow does not prevent the light of the sun from reaching the moon at a full moon. Only when a conjunction or a full moon takes place at (or near) the point where the orbits of the moon and the sun intersect does an eclipse take place.

4.

Because of the revolution of the head, the determination of the moon's longitude will require several stages of computation.

5.

I.e., the head revolves from east to west.

6.

As evident from the later figures given by the Rambam, this number is an approximation, and the actual figure is several thirds less.

7.

The Rambam is giving a negative figure here, his intent being 360° - 180° 57' 28. In positive terms, it would be a position of 179° 2' 32.

8.

This subtraction is necessary, since, as mentioned above, the head revolves from east to west, opposite to the direction of the heavenly sphere as a whole.

Thus, we begin with a negative value as a starting point and add to it the distance traveled by the head. When that total is subtracted from 360, we have a positive figure that is the true position of the head. The reason the Rambam uses a negative figure for his starting point is that as the numbers increase, it is easier to add the mean distance traveled by the head to the starting point of 180° 57' 28 and subtract the total from 360, than to define the starting point in positive terms and subtract the mean progress from it.

9.

As mentioned previously, the head and the tail are the positions where the moon's orbit intersects with that of the sun. Thus, if the moon is at the head or the tail, it is not at all inclined.

10.

We have used a non-literal translation of the word ינפל in this and the following sentence based on the context in this halachah.

11.

I.e., the difference between the position of the moon and the position of the head is less than 180 degrees, as stated in Halachah 10.

12.

I.e., the difference between the position of the moon and the position of the head is more than 180 degrees, as stated in Halachah 10.

13.

The Hebrew term רחב הירח literally means "the width of the moon." It was given this name because its range from 0° to 5° is far less than that of the longitude of the moon, ארך הירח, the angular distance between the moon and the sun, which ranges from 0° to 360°.

14.

According to contemporary science, the Rambam is making an approximation, for the latitude of the moon can reach 5 degrees and 9 minutes.

15.

As indicated from Halachah 11, this is the mid-point between the head and the tail, 90° and 270°.

16.

I.e., the distance the moon has traveled in its orbit from the head to its present position.

17.

This refers to the angle between the plane of the sun's orbit and the position of the moon in its orbit.

18.

As stated above, this is the greatest latitude reached.

19.

See Chapter 13, Halachah 7, and Chapter 15, Halachah 7.

20.

For, as mentioned above, 90 degrees is the even mid-point of the course, and its angle increases and decreases in the same proportions as one approaches or leaves that point.

21.

In the standard printed texts of the Mishneh Torah, there is a printing error, and the concluding phrase from the chapter was added here by mistake.

22.

At 270°, as at 90°, the course reaches its maximum latitude, 5 degrees.

23.

For, as mentioned above, the course begins to increase as it progresses after reaching its tail in the same proportions as it increases as it progresses from its head.

24.

For the rate of the angular decrease from 270 to 180 is equivalent to the rate of decrease from 90 to 180.

## Kiddush HaChodesh - Chapter Seventeen

1

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.

א

כָּל הַדְּבָרִים שֶׁהִקְדַּמְנוּ כְּדֵי שֶׁיִּהְיוּ עֲתִידִים וּמוּכָנִים לִידִיעת הָרְאִיָּה. וּכְשֶׁתִּרְצֶה לָדַעַת זֹאת תַּתְחִיל וְתַחְשֹׁב וְתוֹצִיא מְקוֹם הַשֶּׁמֶשׁ הָאֲמִתִּי וּמְקוֹם הַיָּרֵחַ הָאֲמִתִּי וּמְקוֹם הָרֹאשׁ לִשְׁעַת הָרְאִיָּה. וְתִגְרַע מְקוֹם הַשֶּׁמֶשׁ הָאֲמִתִּי מִמְּקוֹם הַיָּרֵחַ הָאֲמִתִּי וְהַנִּשְׁאָר הוּא הַנִּקְרָא אֹרֶךְ רִאשׁוֹן:

2

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].

ב

וּמֵאַחַר שֶׁתֵּדַע מְקוֹם הָרֹאשׁ וּמְקוֹם הַיָּרֵחַ תֵּדַע מְקוֹם הַיָּרֵחַ כַּמָּה הוּא. וְאִם הוּא רֹחַב צְפוֹנִי אוֹ דְּרוֹמִי וְהוּא הַנִּקְרָא רֹחַב רִאשׁוֹן. וְהִזָּהֵר בָּאֹרֶךְ הַזֶּה הָרִאשׁוֹן וּבָרֹחַב הָרִאשׁוֹן וְיִהְיוּ שְׁנֵיהֶם מוּכָנִים לְךָ:

3

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.

ג

וְהִתְבּוֹנֵן בְּאֹרֶךְ זֶה הָרִאשׁוֹן וּבָרֹחַב הַזֶּה הָרִאשׁוֹן. אִם יֵצֵא לְךָ תֵּשַׁע מַעֲלוֹת בְּשָׁוֶה אוֹ פָּחוֹת. תֵּדַע בְּוַדַּאי שֶׁאִי אֶפְשָׁר לְעוֹלָם שֶׁיֵּרָאֶה הַיָּרֵחַ בְּאוֹתוֹ הַלַּיְלָה בְּכָל אֶרֶץ יִשְׂרָאֵל וְאֵין אַתָּה צָרִיךְ חֶשְׁבּוֹן אַחֵר. וְאִם יִהְיֶה הָאֹרֶךְ הָרִאשׁוֹן יֶתֶר עַל ט''ו מַעֲלוֹת תֵּדַע בְּוַדַּאי שֶׁהַיָּרֵחַ יֵרָאֶה בְּכָל אֶרֶץ יִשְׂרָאֵל וְאֵין אַתָּה צָרִיךְ לְחֶשְׁבּוֹן אַחֵר. וְאִם יִהְיֶה הָאֹרֶךְ הָרִאשׁוֹן מ''ט מַעֲלוֹת וְעַד ט''ו תִּצְטָרֵךְ לִדְרשׁ וְלַחֲקֹר בְּחֶשְׁבּוֹנוֹת הָרְאִיָּה עַד שֶׁתֵּדַע אִם יֵרָאֶה אוֹ לֹא יֵרָאֶה:

4

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

ד

בַּמֶּה דְּבָרִים אֲמוּרִים בְּשֶׁהָיָה מְקוֹם הַיָּרֵחַ הָאֲמִתִּי מִתְּחִלַּת מַזַּל גְּדִי עַד סוֹף מַזַּל תְּאוֹמִים. אֲבָל אִם הָיָה מְקוֹם הַיָּרֵחַ מִתְּחִלַּת מַזַּל סַרְטָן עַד סוֹף מַזַּל קֶשֶׁת וְיִהְיֶה אֹרֶךְ הָרִאשׁוֹן עֶשֶׂר מַעֲלוֹת אוֹ פָּחוֹת. תֵּדַע שֶׁאֵין הַיָּרֵחַ נִרְאֶה כְּלָל בְּאוֹתוֹ הַלַּיְלָה בְּכָל אֶרֶץ יִשְׂרָאֵל. וְאִם הָיָה הָרִאשׁוֹן יֶתֶר עַל כ''ד מַעֲלוֹת וַדַּאי יֵרָאֶה בְּכָל גְּבוּל יִשְׂרָאֵל. וְאִם יִהְיֶה הָאֹרֶךְ הָרִאשׁוֹן מֵעֶשֶׂר מַעֲלוֹת עַד עֶשְׂרִים וְאַרְבַּע תִּצְטָרֵךְ לִדְרשׁ וְלַחֲקֹר בְּחֶשְׁבּוֹנוֹת הָרְאִיָּה אִם יֵרָאֶה אוֹ לֹא יֵרָאֶה:

5

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.

ה

וְאֵלּוּ הֵן חֶשְׁבּוֹנוֹת הָרְאִיָּה. הִתְבּוֹנֵן וּרְאֵה הַיָּרֵחַ בְּאֵיזֶה מַזָּל הוּא. אִם יִהְיֶה בְּמַזַּל טָלֶה תִּגְרַע מִן הָאֹרֶךְ הָרִאשׁוֹן נ''ט חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל שׁוֹר תִּגְרַע מִן הָאֹרֶךְ מַעֲלָה אַחַת. וְאִם יִהְיֶה בְּמַזַּל תְּאוֹמִים תִּגְרַע מִן הָאֹרֶךְ נ''ח חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל סַרְטָן תִּגְרַע מִן הָאֹרֶךְ (מ''ג) [נ''ב] חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל אַרְיֵה תִּגְרַע מִן הָאֹרֶךְ מ''ג חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל בְּתוּלָה תִּגְרַע מִן הָאֹרֶךְ ל''ז חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל מֹאזְנַיִם תִּגְרַע מִן הָאֹרֶךְ ל''ד חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל עַקְרָב תִּגְרַע מִן הָאֹרֶךְ ל''ד חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל קֶשֶׁת תִּגְרַע מִן הָאֹרֶךְ ל''ו חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל גְּדִי תִּגְרַע מִן הָאֹרֶךְ מ''ד חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל דְּלִי תִּגְרַע מִן הָאֹרֶךְ נ''ג חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל דָּגִים תִּגְרַע מִן הָאֹרֶךְ נ''ח חֲלָקִים. וְהַנִּשְׁאָר מִן הָאֹרֶךְ אַחַר שֶׁתִּגְרַע מִמֶּנּוּ אֵלּוּ הַחֲלָקִים הוּא הַנִּקְרָא אֹרֶךְ שֵׁנִי:

6

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.

ו

וְלָמָּה גּוֹרְעִין חֲלָקִים אֵלּוּ. לְפִי שֶׁמְּקוֹם הַיָּרֵחַ הָאֲמִתִּי אֵינוֹ הַמָּקוֹם שֶׁיֵּרָאֶה בּוֹ אֶלָּא שִׁנּוּי יֵשׁ בֵּינֵיהֶם בָּאֹרֶךְ וּבָרֹחַב. וְהוּא הַנִּקְרָא שִׁנּוּי הַמַּרְאֶה. וְשִׁנּוּי מַרְאֵה הָאֹרֶךְ בִּשְׁעַת הָרְאִיָּה לְעוֹלָם גּוֹרְעִין אוֹתוֹ מִן הָאֹרֶךְ כְּמוֹ שֶׁאָמַרְנוּ:

7

[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.

ז

אֲבָל שִׁנּוּי מַרְאֵה הָרֹחַב. אִם הָיָה רֹחַב הַיָּרֵחַ צְפוֹנִי גּוֹרְעִין חֲלָקִים שֶׁל שִׁנּוּי מַרְאֵה הָרֹחַב מִן הָרֹחַב הָרִאשׁוֹן. וְאִם הָיָה רֹחַב הַיָּרֵחַ הַדְּרוֹמִי מוֹסִיפִין הַחֲלָקִים שֶׁל שִׁנּוּי מַרְאֵה הָרֹחַב עַל הָרֹחַב הָרִאשׁוֹן. וּמַה שֶּׁיִּהְיֶה הָרֹחַב הָרִאשׁוֹן אַחַר שֶׁמּוֹסִיפִין עָלָיו אוֹ גּוֹרְעִין מִמֶּנּוּ אוֹתָם הַחֲלָקִים הוּא הַנִּקְרָא רֹחַב שֵׁנִי:

8

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.

ח

וְכַמָּה הֵם הַחֲלָקִים שֶּׁמּוֹסִיפִין אוֹ גּוֹרְעִין אוֹתָן. אִם יִהְיֶה הַיָּרֵחַ בְּמַזַּל טָלֶה תִּשְׁעָה חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל שׁוֹר י' חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל תְּאוֹמִים ט''ז חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל סַרְטָן כ''ז חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל אַרְיֵה ל''ח חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל בְּתוּלָה מ''ד חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל מֹאזְנַיִם מ''ו חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל עַקְרָב מ''ה חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל קֶשֶׁת מ''ד חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל גְּדִי ל''ו חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל דְּלִי (כ''ד) [כ''ז] חֲלָקִים. וְאִם יִהְיֶה בְּמַזַּל דָּגִים י''ב חֲלָקִים:

9

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.

ט

מֵאַחַר שֶׁתֵּדַע חֲלָקִים אֵלּוּ תִּגְרַע אוֹתָן מִן הָרֹחַב הָרִאשׁוֹן אוֹ תּוֹסִיף אוֹתָן עָלָיו כְּמוֹ שֶׁהוֹדַעְנוּךָ וְיֵצֵא לְךָ הָרֹחַב הַשֵּׁנִי. וּכְבָר יָדַעְתָּ אִם הוּא צְפוֹנִי אוֹ דְּרוֹמִי. וְתֵדַע כַּמָּה מַעֲלוֹת וְכַמָּה חֲלָקִים נַעֲשָׂה זֶה הָרֹחַב הַשֵּׁנִי וְתָכִין אוֹתוֹ לְפָנֶיךָ וְיִהְיֶה עָתִיד:

10

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.

י

וְאַחַר כָּךְ תַּחֲזֹר וְתִקַּח מִן הָרֹחַב הַשֵּׁנִי הַזֶּה מִקְצָתוֹ. מִפְּנֵי שֶׁהַיָּרֵחַ נָלוֹז מְעַט בְּמַעְגָּלוֹ. וְכַמָּה הוּא הַמִּקְצָת שֶׁתִּקַּח מִמֶּנּוּ. אִם יִהְיֶה מְקוֹם הַיָּרֵחַ מִתְּחִלַּת מַזַּל טָלֶה עַד כ' מַעֲלוֹת מִמֶּנּוּ. אוֹ מִתְּחִלַּת מַזַּל מֹאזְנַיִם עַד כ' מַעֲלוֹת מִמֶּנּוּ. תִּקַּח מִן הָרֹחַב הַשֵּׁנִי שְׁנֵי חֲמִשָּׁיו. וְאִם יִהְיֶה הַיָּרֵחַ מִכ' מִמַּזַּל טָלֶה עַד י' מַעֲלוֹת מִמַּזַּל שׁוֹר אוֹ מִכ' מִמַּזַּל מֹאזְנַיִם עַד י' מַעֲלוֹת מִמַּזַּל עַקְרָב תִּקַּח מִן הָרֹחַב הַשֵּׁנִי שְׁלִישִׁיתוֹ. וְאִם יִהְיֶה הַיָּרֵחַ מֵעֶשֶׂר מַעֲלוֹת מִמַּזַּל שׁוֹר עַד כ' מִמֶּנּוּ אוֹ מֵעֶשֶׂר מַעֲלוֹת מִמַּזַּל עַקְרָב עַד כ' מִמֶּנּוּ תִּקַּח מִן הָרֹחַב הַשֵּׁנִי רְבִיעִיתוֹ. וְאִם יִהְיֶה הַיָּרֵחַ מִכ' מַעֲלוֹת מִמַּזַּל שׁוֹר עַד סוֹפוֹ אוֹ מִכ' מִמַּזַּל עַקְרָב עַד סוֹפוֹ תִּקַּח מִן הָרֹחַב הַשֵּׁנִי חֲמִישִׁיתוֹ. וְאִם יִהְיֶה הַיָּרֵחַ מִתְּחִלַּת מַזַּל תְּאוֹמִים עַד עֶשֶׂר מַעֲלוֹת מִמֶּנּוּ אוֹ מִתְּחִלַּת מַזַּל קֶשֶׁת עַד עֶשֶׂר מַעֲלוֹת מִמֶּנּוּ תִּקַּח מִן הָרֹחַב הַשֵּׁנִי שְׁתוּתוֹ. וְאִם יִהְיֶה הַיָּרֵחַ מִי' מַעֲלוֹת מִמַּזַּל תְּאוֹמִים וְעַד כ' מִמֶּנּוּ אוֹ מֵעֶשֶׂר מִמַּזַּל קֶשֶׁת עַד כ' מִמֶּנּוּ תִּקַּח מִן הָרֹחַב הַשֵּׁנִי חֲצִי שְׁתוּתוֹ. וְאִם יִהְיֶה מְקוֹם הַיָּרֵחַ מִכ' מִמַּזַּל תְּאוֹמִים עַד כ''ה מִמֶּנּוּ אוֹ מִכ' מִמַּזַּל קֶשֶׁת עַד כ''ה מִמֶּנּוּ תִּקַּח מִן הָרֹחַב הַשֵּׁנִי רְבִיעַ שְׁתוּתוֹ. וְאִם יִהְיֶה מְקוֹם הַיָּרֵחַ מִכ''ה מִמַּזַּל תְּאוֹמִים עַד חָמֵשׁ מַעֲלוֹת מִמַּזַּל סַרְטָן אוֹ מִכ''ה מִמַּזַּל קֶשֶׁת עַד חָמֵשׁ מַעֲלוֹת מִמַּזַּל גְּדִי לֹא תִּקַּח כְּלוּם. לְפִי שֶׁאֵין כָּאן נְלִיזַת מַעְגָּל. וְאִם יִהְיֶה הַיָּרֵחַ מֵחָמֵשׁ מִמַּזַּל סַרְטָן עַד עֶשֶׂר מִמֶּנּוּ אוֹ מֵחָמֵשׁ מִמַּזַּל גְּדִי עַד עֶשֶׂר מִמֶּנּוּ תִּקַּח מִן הָרֹחַב הַשֵּׁנִי רְבִיעַ שְׁתוּתוֹ. וְאִם יִהְיֶה מְקוֹם הַיָּרֵחַ מִי' מִמַּזַּל סַרְטָן עַד כ' מִמֶּנּוּ אוֹ מֵעֶשֶׂר מִמַּזַּל גְּדִי עַד עֶשְׂרִים מִמֶּנּוּ תִּקַּח מִן הָרֹחַב הַשֵּׁנִי חֲצִי שְׁתוּתוֹ. וְאִם יִהְיֶה מְקוֹם הַיָּרֵחַ מִכ' מִמַּזַּל סַרְטָן עַד סוֹפוֹ אוֹ מִכ' מִמַּזַּל גְּדִי עַד סוֹפוֹ תִּקַּח מִן הָרֹחַב הַשֵּׁנִי שְׁתוּתוֹ. וְאִם יִהְיֶה הַיָּרֵחַ מִתְּחִלַּת מַזַּל אַרְיֵה עַד עֶשֶׂר מַעֲלוֹת מִמֶּנּוּ אוֹ מִתְּחִלַּת מַזַּל דְּלִי עַד עֶשֶׂר מַעֲלוֹת מִמֶּנּוּ תִּקַּח מִמֶּנּוּ הָרֹחַב הַשֵּׁנִי חֲמִישִׁיתוֹ. וְאִם יִהְיֶה הַיָּרֵחַ מִי' מַעֲלוֹת מִמַּזַּל אַרְיֵה עַד כ' מִמֶּנּוּ אוֹ מִי' מִמַּזַּל דְּלִי עַד כ' מִמֶּנּוּ תִּקַּח מִן הָרֹחַב הַשֵּׁנִי רְבִיעִיתוֹ. וְאִם יִהְיֶה הַיָּרֵחַ מִכ' מִמַּזַּל אַרְיֵה עַד עֶשֶׂר מִמַּזַּל בְּתוּלָה אוֹ מִכ' מִמַּזַּל דְּלִי עַד עֶשֶׂר מִמַּזַּל דָּגִים תִּקַּח מִן הָרֹחַב הַשֵּׁנִי שְׁלִישִׁיתוֹ. וְאִם יִהְיֶה הַיָּרֵחַ מֵעֶשֶׂר מִמַּזַּל בְּתוּלָה עַד סוֹפוֹ אוֹ מִי' מַעֲלוֹת מִמַּזַּל דָּגִים עַד סוֹפוֹ תִּקַּח מִן הָרֹחַב הַשֵּׁנִי ב' חֲמִשָּׁיו. וְזֹאת הַמִּקְצָת שֶׁתִּקַּח מִן הָרֹחַב הַשֵּׁנִי הִיא הַנִּקְרֵאת מַעְגַּל הַיָּרֵחַ:

11

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.

יא

וְאַחַר כָּךְ תַּחֲזֹר וְתִתְבּוֹנֵן בְּרֹחַב הַיָּרֵחַ וְתִרְאֶה אִם הוּא צְפוֹנִי אוֹ דְּרוֹמִי. אִם הָיָה צְפוֹנִי תִּגְרַע מַעְגַּל הַיָּרֵחַ הַזֶּה מִן הָאֹרֶךְ הַשֵּׁנִי. וְאִם הָיָה רֹחַב הַיָּרֵחַ דְּרוֹמִי תּוֹסִיף הַמַּעְגָּל הַזֶּה עַל הָאֹרֶךְ הַשֵּׁנִי. בַּמֶּה דְּבָרִים אֲמוּרִים כְּשֶׁהָיָה מְקוֹם הַיָּרֵחַ מִתְּחִלַּת מַזַּל גְּדִי עַד סוֹף מַזַּל תְּאוֹמִים. אֲבָל אִם הָיָה הַיָּרֵחַ מִתְּחִלַּת מַזַּל סַרְטָן עַד סוֹף מַזַּל קֶשֶׁת יִהְיֶה הַדָּבָר הֵפֶךְ. שֶׁאִם יִהְיֶה רֹחַב הַיָּרֵחַ צְפוֹנִי תּוֹסִיף הַמַּעְגָּל עַל הָאֹרֶךְ הַשֵּׁנִי. וְאִם הָיָה רֹחַב הַיָּרֵחַ דְּרוֹמִי תִּגְרַע הַמַּעְגָּל מִן הָאֹרֶךְ הַשֵּׁנִי. וּמַה שֶּׁיִּהְיֶה הָאֹרֶךְ הַשֵּׁנִי אַחַר שֶׁתּוֹסִיף עָלָיו אוֹ תִּגְרַע מִמֶּנּוּ הוּא הַנִּקְרָא אֹרֶךְ הַשְּׁלִישִׁי. וְדַע שֶׁאִם לֹא יִהְיֶה שָׁם נְלִיזַת מַעְגָּל וְלֹא נָתַן הַחֶשְׁבּוֹן לָקַחַת מִן הָרֹחַב הַשֵּׁנִי כְּלוּם. יִהְיֶה הָאֹרֶךְ הַשֵּׁנִי עַצְמוֹ הוּא הָאֹרֶךְ הַשְּׁלִישִׁי בְּלֹא פָּחוֹת וּבְלֹא יֶתֶר:

12

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.

יב

וְאַחַר כָּךְ תַּחֲזֹר וְתִרְאֶה הָאֹרֶךְ הַשְּׁלִישִׁי הַזֶּה וְהוּא הַמַּעֲלוֹת שֶׁבֵּין הַיָּרֵחַ וְהַשֶּׁמֶשׁ בְּאֵיזֶה מַזָּל הוּא. אִם יִהְיֶה בְּמַזַּל דָּגִים אוֹ בְּמַזַּל טָלֶה. תּוֹסִיף עַל הָאֹרֶךְ הַשְּׁלִישִׁי שְׁתוּתוֹ. וְאִם יִהְיֶה הָאֹרֶךְ בְּמַזַּל דְּלִי אוֹ בְּמַזַּל שׁוֹר. תּוֹסִיף עַל הָאֹרֶךְ הַשְּׁלִישִׁי חֲמִישִׁיתוֹ. וְאִם יִהְיֶה הָאֹרֶךְ בְּמַזַּל גְּדִי אוֹ בְּמַזַּל תְּאוֹמִים. תּוֹסִיף עַל הָאֹרֶךְ הַשְּׁלִישִׁי שְׁתוּתוֹ. וְאִם יִהְיֶה הָאֹרֶךְ בְּמַזַּל קֶשֶׁת אוֹ בְּמַזַּל סַרְטָן. תָּנִיחַ הָאֹרֶךְ הַשְּׁלִישִׁי כְּמוֹת שֶׁהוּא וְלֹא תּוֹסִיף עָלָיו וְלֹא תִּגְרַע מִמֶּנּוּ. וְאִם הָיָה הָאֹרֶךְ בְּמַזַּל עַקְרָב אוֹ בְּמַזַּל אַרְיֵה. תִּגְרַע מִן הָאֹרֶךְ הַשְּׁלִישִׁי חֲמִישִׁיתוֹ. וְאִם יִהְיֶה הָאֹרֶךְ בְּמַזַּל מֹאזְנַיִם אוֹ בְּמַזַּל בְּתוּלָה. תִּגְרַע מִן הָאֹרֶךְ הַשְּׁלִישִׁי שְׁלִישִׁיתוֹ. וּמַה שֶּׁיִּהְיֶה הָאֹרֶךְ הַשְּׁלִישִׁי אַחַר שֶׁתּוֹסִיף עָלָיו אוֹ תִּגְרַע מִמֶּנּוּ אוֹ תָּנִיחַ אוֹתוֹ כְּמוֹת שֶׁהוּא. הוּא הַנִּקְרָא אֹרֶךְ רְבִיעִי. וְאַחַר כָּךְ תַּחֲזֹר אֵצֶל רֹחַב הַיָּרֵחַ הָרִאשׁוֹן וְתִקַּח שְׁנֵי שְׁלִישָׁיו לְעוֹלָם. וְזֶה הוּא הַנִּקְרָא מְנַת גֹּבַהּ הַמְּדִינָה. וְתִתְבּוֹנֵן וְתִרְאֶה אִם יִהְיֶה רֹחַב הַיָּרֵחַ צְפוֹנִי. תּוֹסִיף מְנַת גֹּבַהּ הַמְּדִינָה עַל הָאֹרֶךְ הָרְבִיעִי. וְאִם יִהְיֶה רֹחַב הַיָּרֵחַ דְּרוֹמִי. תִּגְרַע מְנַת גֹּבַהּ הַמְּדִינָה מִן הָאֹרֶךְ הָרְבִיעִי. וּמַה שֶּׁיִּהְיֶה הָאֹרֶךְ הָרְבִיעִי אַחַר שֶׁגּוֹרְעִין מִמֶּנּוּ אוֹ שֶׁמּוֹסִיפִין עָלָיו הוּא הַנִּקְרָא קֶשֶׁת הָרְאִיָּה:

13

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.

יג

כֵּיצַד. הֲרֵי שֶׁבָּאנוּ לַחְקֹר אִם יֵרָאֶה הַיָּרֵחַ בְּלֵיל עֶרֶב שַׁבָּת שֵׁנִי לְחֹדֶשׁ אִיָּר מִשָּׁנָה זוֹ אוֹ לֹא יֵרָאֶה. תּוֹצִיא מְקוֹם הַשֶּׁמֶשׁ הָאֲמִתִּי וּמְקוֹם הַיָּרֵחַ הָאֲמִתִּי וְרֹחַב הַיָּרֵחַ לְשָׁנָה זוֹ כְּמוֹ שֶׁהוֹדַעְנוּךָ. יֵצֵא לְךָ מְקוֹם הַשֶּׁמֶשׁ הָאֲמִתִּי בְּז' מַעֲלוֹת וְט' חֲלָקִים מִמַּזַּל שׁוֹר. סִימָנוֹ ז''ט. וְיֵצֵא לְךָ מְקוֹם הַיָּרֵחַ הָאֲמִתִּי בְּי''ח מַעֲלוֹת וְל''ו חֲלָקִים מִמַּזַּל שׁוֹר. סִימָנוֹ י''ח ל''ו. וְיֵצֵא לְךָ רֹחַב הַיָּרֵחַ בְּרוּחַ דָּרוֹם שָׁלֹשׁ מַעֲלוֹת וְנ''ג חֲלָקִים. סִימָנוֹ נ''ג ג'. וְזֶה הוּא הָרֹחַב הָרִאשׁוֹן. וְתִגְרַע מְקוֹם הַשֶּׁמֶשׁ מִמְּקוֹם הַיָּרֵחַ יִשָּׁאֵר י''א מַעֲלוֹת וְכ''ז חֲלָקִים. סִימָנוֹ י''א כ''ז. וְזֶה הוּא הָאֹרֶךְ הָרִאשׁוֹן. וּלְפִי שֶׁהָיָה הַיָּרֵחַ בְּמַזַּל שׁוֹר יִהְיֶה שִׁנּוּי מַרְאֵה הָאֹרֶךְ מַעֲלָה אַחַת וְרָאוּי לִגְרֹעַ אוֹתָהּ מִן הָאֹרֶךְ הָרִאשׁוֹן. יֵצֵא לְךָ הָאֹרֶךְ הַשֵּׁנִי י' מַעֲלוֹת וְכ''ז חֲלָקִים. סִימָנוֹ יכ''ז. וְכֵן יִהְיֶה שִׁנּוּי מַרְאֵה הָרֹחַב י' חֲלָקִים. וּלְפִי שֶׁרֹחַב הַיָּרֵחַ הָיָה דְּרוֹמִי רָאוּי לְהוֹסִיף עָלָיו שִׁנּוּי הַמַּרְאֶה שֶׁהוּא עֲשָׂרָה חֲלָקִים. יֵצֵא לְךָ הָרֹחַב הַשֵּׁנִי ד' מַעֲלוֹת וְג' חֲלָקִים. סִימָנוֹ ד''ג. וּלְפִי שֶׁהָיָה הַיָּרֵחַ בְּי''ח מַעֲלוֹת מִמַּזַּל שׁוֹר רָאוּי לִקַּח מִן הָרֹחַב הַשֵּׁנִי רְבִיעִיתוֹ וְהוּא הַנִּקְרָא מַעְגַּל הַיָּרֵחַ. יֵצֵא לְךָ מַעְגַּל הַיָּרֵחַ לְעֵת זוֹ מַעֲלָה אַחַת וְחֵלֶק אֶחָד לְפִי שֶׁאֵין מְדַקְדְּקִין בִּשְׁנִיּוֹת:

14

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.

יד

וּלְפִי שֶׁרֹחַב הַיָּרֵחַ דְּרוֹמִי וּמְקוֹם הַיָּרֵחַ הָאֲמִתִּי בֵּין רֹאשׁ גְּדִי וְרֹאשׁ סַרְטָן. רָאוּי לְהוֹסִיף הַמַּעְגָּל עַל הָאֹרֶךְ הַשֵּׁנִי. יֵצֵא לְךָ הָאֹרֶךְ הַשְּׁלִישִׁי י''א מַעֲלוֹת וְכ''ח חֲלָקִים. סִימָנוֹ י''א כ''ח. וּלְפִי שֶׁהָאֹרֶךְ הַזֶּה בְּמַזַּל שׁוֹר רָאוּי לְהוֹסִיף עַל הָאֹרֶךְ הַשְּׁלִישִׁי חֲמִישִׁיתוֹ שֶׁהוּא שְׁתֵּי מַעֲלוֹת וְי''ח חֲלָקִים. וְיֵצֵא לְךָ הָאֹרֶךְ הָרְבִיעִי י''ג מַעֲלוֹת וּמ''ו חֲלָקִים. סִימָנוֹ י''ג מ''ו. וְחָזַרְנוּ אֵצֶל הָרֹחַב הָרִאשׁוֹן וְלָקַחְנוּ שְׁנֵי שְׁלִישָׁיו וְיֵצֵא מְנַת גֹּבַהּ הַמְּדִינָה וְהוּא שְׁתֵּי מַעֲלוֹת וְל''ה חֲלָקִים. וּלְפִי שֶׁהָיָה הָרֹחַב דְּרוֹמִי. רָאוּי לִגְרֹעַ מִמֶּנּוּ מְנַת גֹּבַהּ הַמְּדִינָה מִן הָאֹרֶךְ הָרְבִיעִי. יִשָּׁאֵר לְךָ י''א מַעֲלוֹת וְי''א חֲלָקִים. סִימָנוֹ י''א י''א. וְזוֹ הִיא קֶשֶׁת הָרְאִיָּה בַּלַּיְלָה הַזֶּה. וְעַל הַדֶּרֶךְ הַזֶּה תַּעֲשֶׂה וְתֵדַע קֶשֶׁת הָרְאִיָּה כַּמָּה מַעֲלוֹת וְכַמָּה חֲלָקִים יֵשׁ בָּהּ בְּכָל לֵיל רְאִיָּה שֶׁתִּרְצֶה לְעוֹלָם:

15

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.

טו

וְאַחַר שֶׁתֵּצֵא קֶשֶׁת זוֹ תָּבִין בָּהּ. וְדַע שֶׁאִם תִּהְיֶה קֶשֶׁת הָרְאִיָּה תֵּשַׁע מַעֲלוֹת אוֹ פָּחוֹת אָז אֶפְשָׁר שֶׁיֵּרָאֶה בְּכָל אֶרֶץ יִשְׂרָאֵל. וְאִם תִּהְיֶה קֶשֶׁת הָרְאִיָּה יֶתֶר עַל י''ד מַעֲלוֹת אִי אֶפְשָׁר שֶׁלֹּא יֵרָאֶה וְיִהְיֶה גָּלוּי לְכָל אֶרֶץ יִשְׂרָאֵל:

16

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.

טז

וְאִם תִּהְיֶה קֶשֶׁת הָרְאִיָּה מִתְּחִלַּת מַעֲלָה עֲשִׂירִית עַד סוֹף מַעֲלַת י''ד. תַּעֲרֹךְ קֶשֶׁת הָרְאִיָּה אֶל הָאֹרֶךְ הָרִאשׁוֹן וְתֵדַע אִם יֵרָאֶה אוֹ לֹא יֵרָאֶה מִן הַקִּצִּין שֶׁיֵּשׁ לוֹ. וְהֵן הַנִּקְרָאִין קִצֵּי הָרְאִיָּה:

17

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.

יז

וְאִלּוּ הֵן קִצֵּי הָרְאִיָּה. אִם תִּהְיֶה קֶשֶׁת הָרְאִיָּה מִיֶּתֶר עַל ט' מַעֲלוֹת עַד סוֹף עֶשֶׂר מַעֲלוֹת אוֹ יֶתֶר עַל עֶשֶׂר. וְיִהְיֶה הָאֹרֶךְ הָרִאשׁוֹן י''ג מַעֲלוֹת אוֹ יוֹתֵר. וַדַּאי יֵרָאֶה. וְאִם תִּהְיֶה הַקֶּשֶׁת פָּחוֹת מִזֶּה אוֹ יִהְיֶה הָאֹרֶךְ פָּחוֹת מִזֶּה לֹא יֵרָאֶה:

18

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.

יח

וְאִם תִּהְיֶה קֶשֶׁת הָרְאִיָּה מִיֶּתֶר עַל עֶשֶׂר מַעֲלוֹת עַד סוֹף י''א מַעֲלוֹת אוֹ יֶתֶר עַל אַחַת עֶשְׂרֵה. וְיִהְיֶה הָאֹרֶךְ הָרִאשׁוֹן י''ב מַעֲלוֹת אוֹ יוֹתֵר. וַדַּאי יֵרָאֶה. וְאִם תִּהְיֶה הַקֶּשֶׁת פָּחוֹת מִזֶּה אוֹ יִהְיֶה הָאֹרֶךְ פָּחוֹת מִזֶּה לֹא יֵרָאֶה:

19

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.

יט

וְאִם תִּהְיֶה קֶשֶׁת הָרְאִיָּה מִיֶּתֶר עַל י''א עַד סוֹף י''ב מַעֲלוֹת אוֹ יֶתֶר עַל י''ב. וְיִהְיֶה הָאֹרֶךְ הָרִאשׁוֹן י''א מַעֲלוֹת אוֹ יוֹתֵר וַדַּאי יֵרָאֶה. וְאִם תִּהְיֶה הַקֶּשֶׁת פָּחוֹת מִזֶּה אוֹ יִהְיֶה הָאֹרֶךְ פָּחוֹת מִזֶּה לֹא יֵרָאֶה:

20

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.

כ

וְאִם תִּהְיֶה קֶשֶׁת הָרְאִיָּה מִיֶּתֶר עַל י''ב מַעֲלוֹת עַד סוֹף י''ג מַעֲלוֹת אוֹ יֶתֶר עַל י''ג. וְיִהְיֶה הָאֹרֶךְ הָרִאשׁוֹן י' מַעֲלוֹת אוֹ יוֹתֵר וַדַּאי יֵרָאֶה. וְאִם תִּהְיֶה הַקֶּשֶׁת פָּחוֹת מִזֶּה אוֹ יִהְיֶה הָאֹרֶךְ פָּחוֹת מִזֶּה לֹא יֵרָאֶה:

21

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.

כא

וְאִם תִּהְיֶה הָרְאִיָּה מִיֶּתֶר עַל י''ג מַעֲלוֹת עַד סוֹף י''ד מַעֲלוֹת אוֹ יֶתֶר עַל י''ד. וְיִהְיֶה הָאֹרֶךְ הָרִאשׁוֹן תֵּשַׁע מַעֲלוֹת אוֹ יוֹתֵר וַדַּאי יֵרָאֶה. וְאִם תִּהְיֶה הַקֶּשֶׁת פָּחוֹת מִזֶּה אוֹ יִהְיֶה הָאֹרֶךְ פָּחוֹת מִזֶּה לֹא יֵרָאֶה. וְעַד כָּאן סוֹף הַקִּצִּין:

22

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.

כב

כֵּיצַד. בָּאנוּ לְהִתְבּוֹנֵן בְּקֶשֶׁת הָרְאִיָּה שֶׁל לֵיל עֶרֶב שַׁבָּת שֵׁנִי לְחֹדֶשׁ אִיָּר מִשָּׁנָה זוֹ. יֵצֵא לָנוּ בְּחֶשְׁבּוֹן קֶשֶׁת הָרְאִיָּה י''א מַעֲלוֹת וְי''א חֲלָקִים כְּמוֹ שֶׁיָּדַעְתָּ. וּלְפִי שֶׁהָיָה קֶשֶׁת הָרְאִיָּה בֵּין עֶשֶׂר עַד אַרְבַּע עֶשְׂרֵה עָרַכְנוּ אוֹתָהּ אֶל הָאֹרֶךְ הָרִאשׁוֹן. וּכְבָר יָדַעְתָּ שֶׁהָאֹרֶךְ הָיָה בְּלֵיל זֶה י''א מַעֲלוֹת וְכ''ז חֲלָקִים. וּלְפִי שֶׁהָיְתָה קֶשֶׁת הָרְאִיָּה יֶתֶר עַל י''א מַעֲלוֹת וְהָיָה הָאֹרֶךְ הָרִאשׁוֹן יֶתֶר עַל עֲשָׂרָה [א.] יוֹדֵעַ שֶׁוַּדַּאי יֵרָאֶה בְּלֵיל זֶה לְפִי הַקִּצִּין הַקְּצוּבוֹת. וְכֵן תִּשְׁעָה בְּכָל קֶשֶׁת וָקֶשֶׁת עִם הָאֹרֶךְ הָרִאשׁוֹן שֶׁלָּהּ:

23

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.

כג

וּכְבָר רָאִיתָ מִן הַמַּעֲשִׂים הָאֵלּוּ כַּמָּה חֶשְׁבּוֹנוֹת יֵשׁ בּוֹ וְכַמָּה תּוֹסָפוֹת וְכַמָּה גֵּרוּעִין אַחַר שֶׁיָּגַעְנוּ הַרְבֵּה. עַד שֶׁהִמְצִיאָנוּ דְּרָכִים קְרוֹבִים שֶׁאֵין בְּחֶשְׁבּוֹנָם עֹמֶק גָּדוֹל. שֶׁהַיָּרֵחַ עֲקַלְקַלּוֹת גְּדוֹלוֹת יֵשׁ בְּמַעְגְּלוֹתָיו. וּלְפִיכָךְ אָמְרוּ חֲכָמִים (תהילים קד יט) "שֶׁמֶשׁ יָדַע מְבוֹאוֹ" יָרֵחַ לֹא יָדַע מְבוֹאוֹ. וְאָמְרוּ חֲכָמִים פְּעָמִים בָּא בַּאֲרֻכָּה פְּעָמִים בָּא בִּקְצָרָה. כְּמוֹ שֶׁתִּרְאֶה מֵחֶשְׁבּוֹנוֹת אֵלּוּ שֶׁפְּעָמִים תּוֹסִיף וּפְעָמִים תִּגְרַע עַד שֶׁתְּהֵא קֶשֶׁת הָרְאִיָּה. וּפְעָמִים תִּהְיֶה קֶשֶׁת הָרְאִיָּה אֲרוּכָּה וּפְעָמִים קְצָרָה כְּמוֹ שֶׁבֵּאַרְנוּ:

24

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

כד

וְטַעַם כָּל אֵלּוּ הַחֶשְׁבּוֹנוֹת וּמִפְּנֵי מָה מוֹסִיפִים מִנְיָן זֶה וּמִפְּנֵי מָה גּוֹרְעִין. וְהֵיאַךְ נוֹדַע כָּל דָּבָר וְדָבָר מֵאֵלּוּ הַדְּבָרִים. וְהָרְאָיָה עַל כָּל דָּבָר וְדָבָר. הִיא חָכְמַת הַתְּקוּפוֹת וְהַגִּימַטְרִיּוֹת שֶׁחִבְּרוּ בָּהּ חַכְמֵי יָוָן סְפָרִים הַרְבֵּה וְהֵם הַנִּמְצָאִים עַכְשָׁו בְּיַד הַחֲכָמִים. אֲבָל הַסְּפָרִים שֶׁחִבְּרוּ חַכְמֵי יִשְׂרָאֵל שֶׁהָיוּ בִּימֵי הַנְּבִיאִים מִבְּנֵי יִשָּׂשכָר לֹא הִגִּיעוּ אֵלֵינוּ. וּמֵאַחַר שֶׁכָּל אֵלּוּ הַדְּבָרִים בִּרְאָיוֹת בְּרוּרוֹת הֵם שֶׁאֵין בָּהֶם דֹּפִי וְאִי אֶפְשָׁר לְאָדָם לְהַרְהֵר אַחֲרֵיהֶם, אֵין חוֹשְׁשִׁין לַמְחַבֵּר בֵּין שֶׁחִבְּרוּ אוֹתָם נְבִיאִים בֵּין שֶׁחִבְּרוּ אוֹתָם הָאֻמּוֹת. שֶׁכָּל דָּבָר שֶׁנִּתְגַּלָּה טַעֲמוֹ וְנוֹדְעָה אֲמִתָּתוֹ בִּרְאָיוֹת שֶׁאֵין בָּהֶם דֹּפִי אָנוּ סוֹמְכִין עַל זֶה הָאִישׁ שֶׁאֲמָרוֹ אוֹ שֶׁלִּמְּדוֹ עַל הָרְאָיָה שֶׁנִּתְגַּלְּתָה וְהַטַּעַם שֶׁנּוֹדַע:

Footnotes
1.

Our translation is based on authentic manuscript editions of the Mishneh Torah and early printings. There is a printing error in the standard published text.

2.

In this instance as well, our translation is based on authentic manuscript editions of the Mishneh Torah and early printings. There is a printing error in the standard published text, where the words "and the first latitude" were added unnecessarily.

3.

Note the apparent contradiction to the figures the Rambam mentions in Chapter 15, Halachah 2, and the resolution suggested in Note 4 of that chapter.

4.

In these months, the ecliptic (the plane of the sun's orbit as extended to the celestial sphere) is inclined to the north. After the conjunction, the moon proceeds away from the position of the sun. When the inclination of the ecliptic is northward, this movement places it in a more northerly position. Therefore, the moon will set later than would be foreseen otherwise, resulting in a greater possibility of seeing the new moon.

As mentioned in the notes of Chapter 16, as the longitude of the moon increases, seeing the moon also becomes easier. In these months, however, a lesser longitude is required.

5.

In these months, the ecliptic is inclined to the south. As the moon proceeds away from the position of the sun after conjunction, it will be in a more southerly position in these months. Therefore,the moon will set earlier than would be foreseen otherwise, resulting in a lesser possibility of seeing the new moon. To compensate for this difference, a greater longitude is required.

6.

Our translation is based on authentic manuscript editions of the Mishneh Torah and early printings. There is a printing error in the standard published text, and the word "latitude" was added unnecessarily.

7.

To summarize the Rambam's statements to this point: When the longitude of the moon (the angular distance between the moon and the sun) is minimal, the moon's crescent will be small and the interval between the time of its setting and that of the sun will be small. Hence, it is unlikely that the moon will be sighted.

When the longitude of the moon is greater, the size of the moon's crescent will increase, as will the interval between the time of its setting and that of the sun. Accordingly, the possibility of sighting the moon will increase.

When the longitude is significantly large, it is obvious that the moon will be seen and no other calculations are necessary. When, however, the longitude is of intermediate size, there is a question whether the moon will be seen. The resolution of this question depends on the inclination of the ecliptic and the latitude of the moon - i.e., the angle - and the direction of that angle - to which the moon is inclined from the plane of the sun.

[In this context, it is worthy to mention a question raised by several contemporary commentaries on Hilchot Kiddush HaChodesh: Seemingly, there is a direct connection between the concepts mentioned at the conclusion of Chapter 15 and those mentioned at the beginning of this chapter. Why does the Rambam interpose the discussion of the moon's latitude (the subject matter of Chapter 16, which becomes relevant only in subsequent halachot) between them?]

8.

The sighting adjustment for longitude is based on two different factors: a) whether the constellation is inclined to the north or to the south as it intersects the horizon of Jerusalem, and b) the extent of the southerly position of that constellation.

To explain: The constellations intersect the horizon at different angles, reflecting the pattern of their inclination in the heavenly sphere. The constellations from Capricorn until Gemini intersect the horizon at a northerly angle, and the constellations from Cancer to Sagittarius intersect the horizon at a southerly angle.

With regard to the second factor, all the constellations are located to the south of Jerusalem. Jerusalem is located 32 degrees north, and the constellation of Cancer, the most northerly of the constellations, is located 23 1/2 degrees north. The more northerly a constellation is located, however, the greater the need for a subtraction from its longitude.

9.

This is the constellation that the moon enters at the vernal (spring) equinox. It is inclined to the north and is not located in an extremely southerly position. Hence, a large sighting adjustment is necessary.

10.

Since the constellation of Taurus intersects the horizon at a northerly inclination and it is located in a relatively northerly position, the largest adjustment is necessary.

11.

Although this constellation is located in a very northerly position, its northerly inclination is less. Hence, a smaller subtraction is made.

12.

Here, too, our translation is an emendation of the standard published text, based on authentic manuscript editions of the Mishneh Torah and early printings.

Although Cancer is located in the most northerly position of all the constellations, since it has a southerly inclination the sighting adjustment required is less.

13.

This and the four constellations that follow have southerly inclinations. Hence, the figure subtracted from their longitude is less.

14.

This is the smallest sighting adjustment, because this constellation is located in a more southerly position than the others with a southerly inclination.

15.

From this point on, the sighting adjustment increases, because these constellations have a northerly inclination.

16.

The commentaries have noted that although the general thrust of the adjustments suggested by the Rambam conform to the calculations of the astronomers, the exact figures he gives follow neither the classic Greek figures nor those of modern astronomy. It is possible to explain that the Rambam was speaking merely in approximations, giving us a figure useful enough to calculate the position where the moon would be sighted, but not an exact scientific measure. This theory is borne out by the fact that he does not provide different measures for northern and southern latitudes, although according to science these figures vary.

17.

To explain: The true position of the moon reflects the line extending from the center of the earth through the center of the moon, as it is projected against the heavenly sphere. Since Jerusalem (or for that matter, any other location on the earth's surface) is not located at the center of the earth, but rather 4000 miles away, there will be a slight difference between the line described previously and the line extending from a person standing in Jerusalem to the center of the moon, as it is projected against the heavenly sphere. The closer the moon is to the horizon, the larger the sighting adjustment that has to be made.

[The same concept applies with regard to the sun. Nevertheless, since the distance between the earth and the sun is great, the angular difference between these two lines is not of consequence. The moon, by contrast, is located much closer to the earth and, at times, a difference of close to a degree can arise.]

In the evening, the moon will always appear slightly closer to the horizon than it actually is - i.e., it will appear closer to the position of the sun. Therefore, the angular difference between the two lines mentioned above should be subtracted from the moon's true position. As explained above, the extent of the adjustment to be made depends on the inclination at which constellation intersects the horizon and its latitude in the heavenly sphere.

18.

This principle applies during all the PM hours. During the AM hours, by contrast, the sighting adjustment should be added to the position of the moon (Ralbach).

19.

The sighting adjustment for the moon's latitude is derived by creating a parallax - i.e., a line directly parallel to the line running from the point of the moon's first longitude to its first latitude is drawn from the point of its second longitude. A second line is drawn from the position of an onlooker in Jerusalem through the point of the first latitude and intersecting the line of the moon's second latitude. The point where these two lines intersect is the moon's second longitude. The adjustment mentioned in the following halachah represents the angle between these two lines.

20.

Because Jerusalem is situated in a more northerly position than all the Zodiac constellations, the moon will always appear more southerly than it actually is. Therefore, if its latitude is northerly, a subtraction is necessary. To use geometric terms: When the moon's latitude is northerly, its second latitude will always be closer to the point of its longitude than to its first latitude.

21.

Since the moon will always appear more southerly, an addition is required when its original latitude is southerly. In geometric terms: When the moon's latitude is southerly, its second latitude will always be further removed from the point of its longitude than its first latitude.

22.

This is the point directly after the vernal (spring) equinox, when the sun is inclined northward and enters the northern part of its orbit.

23.

This is the point directly after the autumnal equinox, when the sun is inclined southward and enters the southern part of its orbit.

24.

Here, too, our translation is an emendation of the standard published text, based on authentic manuscript editions of the Mishneh Torah and early printings.

25.

The Rambam is speaking about the second latitude, since it is possible for the sighting adjustment to change a northerly latitude to a southerly one.

26.

The purpose of the calculations that follow (reaching a third longitude and a fourth longitude) is to calculate the time between the setting of the sun and the setting of the moon. The first longitude is sufficient to inform us whether or not the crescent of the moon will be large enough to be visible. The subsequent calculations are necessary to determine whether or not there will be sufficient time for actually sighting the moon. For when the crescent is small, it is difficult to detect unless there is ample time before it sets.

The third longitude reflects the point in the celestial sphere that will set at the same time as the moon does, as seen by a person standing on the equator. This is not the point in the celestial sphere where the moon appears to be located, but rather a point in the celestial sphere that is reached by drawing a line originating at the equator, running parallel to the horizon of the equator, and extending through the center of the moon. The point where this line intersects the celestial sphere is the third longitude.

The reason for associating the moon's position with the equator is to establish a connection with a standard measure of time. In Jerusalem (and for that matter, anywhere else in the northern or southern hemisphere), the apparent movement of the celestial sphere varies with the seasons. On the equator, by contrast, the movement of the celestial sphere is constant at all times, 15 minutes to the hour.

28.

The angle between each particular constellation in the celestial sphere and the equator varies. The size of the adjustment to be made for the third longitude depends on that angle.

29.

These are the points in the celestial sphere that intersect the horizon of the equator at the greatest angle. Therefore, the largest adjustment is necessary.

30.

These are the points within the celestial sphere that are more or less parallel to the equator.

31.

This means that when the moon's latitude is northerly, the third longitude will always be closer to the equator.

32.

This means that when the moon's latitude is southerly, the third longitude will always be further removed from the equator.

33.

These are the constellations that are inclined in a northerly direction.

34.

I.e., the constellations that are inclined in a southerly direction.

35.

This means that when the moon's latitude is northerly, the third longitude will always be further removed from the equator.

36.

This means that when the moon's latitude is southerly, the third longitude will always be closer to the equator.

37.

As happens when the moon is located in the beginning of the constellations of Cancer and Capricorn.

38.

The Rambam's intent in these sets of calculations is to reach a point on the equator that will set at the same time the third longitude sets in Jerusalem. For although the third longitude was able to relate the moon's position to the equator, it did not take into consideration the difference between the horizon of the equator and the horizon of Jerusalem. This is accomplished by drawing a line from the third longitude to the equator, which is parallel to the horizon of Jerusalem.

39.

Two factors are significant in determining the fourth longitude: a) The angle of the constellation's inclination to the horizon of the equator. The greater the inclination of the constellation, the closer the fourth longitude will be located to the equator.

b) whether the constellation is inclined to the north or to the south.

If the constellation is inclined to the north, the third longitude, and hence the place on the equator parallel to it, will be located further away from the horizon, resulting in a later setting and thus an extended fourth longitude. Conversely, if the inclination is southerly, the third longitude will be located closer to the horizon, resulting in a shortened fourth longitude.

Of these two factors, the latter is more significant, and causes a larger correction. To explain these factors with regard to the constellations of Pisces and Aries: These constellations are inclined to a great degree, a factor that would reduce the fourth longitude. Since, however, they are northerly inclined, and this is the stronger factor, a modest increase is required.

40.

These constellations are inclined to the north, and the degree of their inclination is less than that of Pisces and Aries. Hence, a greater increase is required.

41.

Here, the constellations begin a southerly inclination. Hence, although they are more parallel to the horizon of the equator, no addition is made.

42.

In this instance, the degree of inclination of these constellations is great and their inclination is southerly. Both of these factors lead to a reduction in the fourth longitude. Hence, the greatest subtraction is required.

43.

The Ralbach questions why the Rambam refers to the first latitude. Seemingly, it would be appropriate to make this correction based on the second latitude, for there is a significant difference between it and the first latitude. According to trigonometry, it also would appear that the calculations should be based on the second latitude.

44.

Although the fourth longitude established a relationship between the equator and Jerusalem, it is still dependent on the third longitude, which relates to the moon and the celestial sphere as they set on the horizon of the equator. Through the correction mentioned here, we find a place on the extension of the equator that will set at the same as the moon sets in Jerusalem. Having reached this point, we can calculate the difference in time (15 degrees to the hour) between the setting of the sun and this point (which will set at the same time as the setting of the moon). Accordingly, we will be able to determine whether or not this interval will allow for the sighting of the moon.

The correction for geographic longitude is reached by drawing a line from the position of the moon parallel to the horizon of Jerusalem. One might ask: If this was the Rambam's intent, why were so many intermediate steps - the definition of the second, third, and fourth latitudes - necessary? Why didn't he suggest drawing the above- mentioned line at the very beginning of his calculations?

The explanation is that the Rambam allowed an individual to follow his own steps in arriving at this final figure. I.e., these lines and distances are all artificial and can be determined only by calculations. Through trigonometry, if one knows the length of one side of a triangle and two angles, or the length of two sides and one angle, it is possible to calculate the size of all three angles and all three sides. To find the line extending from the moon to the equator parallel to the horizon of Jerusalem, the Rambam had to build sets of triangles, and calculate angles based on the relationship of one triangle to another. The process he followed is reflected in the series of corrections he offers.

45.

A northerly latitude means that the actual position of the moon is further removed from the horizon than the third longitude. This will result in a later setting of the moon. Accordingly, the correction based on geographic latitude will require addition to the fourth longitude. This applies regardless of whether the inclination of the constellation in which the moon is located is northerly or southerly.

46.

A southerly latitude means that the actual position of the moon is closer to the horizon than the third longitude. This will result in an earlier setting of the moon. Accordingly, the correction based on geographic latitude will require subtraction from the fourth longitude. This applies regardless of whether the inclination of the constellation in which the moon is located is northerly or southerly.

47.

Our translation represents a correction of the standard printed text of the Mishneh Torah.

48.

It is possible that the Rambam's wording alludes to a concept mentioned previously, that the calculations he suggests are applicable only at the beginning of the month, when the new moon might be sighted.

49.

I.e., barring clouds, as explained at the beginning of the following chapter.

50.

As mentioned at the beginning of this chapter, the first longitude gives us information regarding the size of the moon's crescent and the difference between the moon's setting and that of the sun. When the first longitude is sufficiently large or when it is sufficiently small, it is possible to determine whether or not the moon will be sighted without considering extenuating factors - e.g., its longitude, the inclination of the constellation in which it is located, and the extent of that inclination. When, however, the first longitude is of intermediate length, these extenuating factors must be considered. The establishment of a systematic method of considering these factors is the purpose of all the computations mentioned in this chapter.

51.

See Halachot 13 and 14.

52.

As the Rambam mentioned at the very beginning of this discussion (Chapter 11, Halachah 6), the figures that he gives are not exact. They do, however, give us sufficient information to determine when and where the moon will be sighted.

53.

Rosh HaShanah 25a, commenting on Psalms 104:19.

54.

Loc. cit.

55.

Commenting on I Chronicles 12:32, "From the descendants of Yissachar, men who had understanding of the times...," Bereshit Rabbah 72:5 explains that the sages of the tribe of Yissachar were those responsible for the determination of the calendar. (See also the commentary of the Radak on this verse.)

56.

The context of this commentary is not a proper place for a full discussion of the Rambam's perspective on the supposed conflicts between science and the Torah. It must be noted, however, that the statements made here, emphasizing the importance of the empirical evidence of science, should not be interpreted as indicating that the perspective science adopts at any given time should be accepted in place of the Torah's teachings. In this context, it is worthy to quote the Rambam's statements in Hilchot Shechitah 10:13:

Similarly, with regard to the conditions that we have enumerated as causing an animal to be trefah (unable to live for an extended period): Even though it appears from the medical knowledge available to us at present that some of these conditions are not fatal... all that is significant to us is what our Sages said, as [implied by Deuteronomy 17:11]: "[You shall act] according to the instructions that they will give you."

57.

Our translation is based on authoritative manuscripts and early printings of the Mishneh Torah; it differs slightly from the standard printed text.