The Rambam · Sefer Zemanim
הלכות קידוש החודש י״אSanctification of the New Month 11
Chapter 11 of 19 in Sanctification of the New Month — 17 halachot
Halacha 1א׳
לְפִי שֶׁאָמַרְנוּ בַּהֲלָכוֹת אלּוּ שֶׁבֵּית דִּין הָיוּ מְחַשְּׁבִין בְּדִקְדּוּק וְיוֹדְעִים אִם יֵרָאֶה הַיָּרֵחַ אוֹ לֹא יֵרָאֶה. יָדַעְנוּ שֶׁכָּל מִי שֶׁרוּחוֹ נְכוֹנָה וְלִבּוֹ תָּאֵב לְדִבְרֵי הַחָכְמוֹת וְלַעֲמֹד עַל הַסּוֹדוֹת יִתְאַוֶּה לֵידַע אוֹתָן הַדְּרָכִים שֶׁמְּחַשְּׁבִין בָּהֶם עַד שֶׁיֵּדַע אָדָם אִם יֵרָאֶה הַיָּרֵחַ בְּלַיִל זֶה אוֹ לֹא יֵרָאֶה:
Since we said in these laws that the court would calculate with precision and know whether the moon was seen or it was not seen – we have known that anyone whose spirit is correct and whose heart desires matters of wisdom and to understand the secrets will want to know the ways with which they calculated to the point that one would know if the moon would be seen on this night or not be seen.
Halacha 2ב׳
וְדַרְכֵי הַחֶשְׁבּוֹן יֵשׁ בָּהֶן מַחֲלוֹקוֹת גְּדוֹלוֹת בֵּין חַכְמֵי הַגּוֹיִם הַקַּדְמוֹנִים שֶׁחָקְרוּ עַל חֶשְׁבּוֹן הַתְּקוּפוֹת וְהַגִּימַטְרִיָּאוֹת. וַאֲנָשִׁים חֲכָמִים גְּדוֹלִים נִשְׁתַּבְּשׁוּ בָּהֶן וְנִתְעַלְּמוּ מֵהֶן דְּבָרִים וְנוֹלְדוּ לָהֶן סְפֵקוֹת. וְיֵשׁ מִי שֶׁדִּקְדֵּק הַרְבֵּה וְלֹא פָּגַע בַּדֶּרֶךְ הַנְּכוֹנָה בְּחֶשְׁבּוֹן רְאִיַּת הַיָּרֵחַ אֶלָּא צָלַל בְּמַיִם אַדִּירִים וְהֶעֱלָה חֶרֶס בְּיָדוֹ:
And there are great disagreements among the early sages of the nations who researched the calculation of the seasons and [mathematics]. And very wise people got confounded with them and missed things and questions arose for them. And there was one who was very exacting and [yet] did not encounter the correct way in the calculation of the sighting of the moon, but rather floated on great waters but [only] brought up clay in his hand.
Halacha 3ג׳
וּלְפִי אֹרֶךְ הַיָּמִים וְרֹב הַבְּדִיקוֹת וְהַחֲקִירוֹת נוֹדְעוּ לְמִקְצָת הַחֲכָמִים דַּרְכֵי חֶשְׁבּוֹן זֶה. וְעוֹד שֶׁיֵּשׁ לָנוּ בְּעִקָּרִים אֵלּוּ קַבָּלוֹת מִפִּי הַחֲכָמִים וּרְאָיוֹת שֶׁלֹּא נִכְתְּבוּ בַּסְּפָרִים הַיְדוּעִים לַכּל. וּמִפְּנֵי כָּל אֵלּוּ הַדְּבָרִים כָּשֵׁר בְּעֵינַי לְבָאֵר דַּרְכֵי חֶשְׁבּוֹן זֶה כְּדֵי שֶׁיִּהְיֶה נָכוֹן לְמִי שֶׁמְּלָאוֹ לִבּוֹ לְקָרְבָה אֶל הַמְּלָאכָה לַעֲשׂוֹת אוֹתָהּ:
And due to the length of the years and the multitude of experiments and research, the ways of this calculation became known to some sages. Moreover we have traditions and proofs from the Sages about their main principles written in books that are not known to all. And because of all these things, it is fitting in my eyes to explain the ways of this calculation – in order that it be prepared for the one whose heart fills him to approach this discipline to do it.
Mishneh Torah, Torat Emet 363 edition, via Sefaria — public domain
English: Sefaria Edition, tr. R. Francis Nataf, 2019 — CC BY