The Jewish Calendar and Jewish Astronomy Source Sheet

(ו) וּשְׁמַרְתֶּם֮ וַעֲשִׂיתֶם֒ כִּ֣י הִ֤וא חָכְמַתְכֶם֙ וּבִ֣ינַתְכֶ֔ם לְעֵינֵ֖י הָעַמִּ֑ים אֲשֶׁ֣ר יִשְׁמְע֗וּן אֵ֚ת כָּל־הַחֻקִּ֣ים הָאֵ֔לֶּה וְאָמְר֗וּ רַ֚ק עַם־חָכָ֣ם וְנָב֔וֹן הַגּ֥וֹי הַגָּד֖וֹל הַזֶּֽה׃

Deuteronomy 4:6

(6) Observe them faithfully, for that will be proof of your wisdom and discernment to other peoples, who on hearing of all these laws will say, “Surely, that great nation is a wise and discerning people.”

One may ask an obvious question. Since when will the nations of the world see any wisdom in our observance of Shabbat, Kashrut, Sha'atnez etc? They certainly do not attribute any wisdom to us on that account!

Obviously, it must refer to another sort of Jewish Wisdom

דברי הימים א י״ב:ל״ג

(לג) וּמִבְּנֵ֣י יִשָּׂשכָ֗ר יוֹדְעֵ֤י בִינָה֙ לַֽעִתִּ֔ים לָדַ֖עַת מַה־יַּעֲשֶׂ֣ה יִשְׂרָאֵ֑ל רָאשֵׁיהֶ֣ם מָאתַ֔יִם וְכָל־אֲחֵיהֶ֖ם עַל־פִּיהֶֽם׃ (ס)

I Chronicles 12:33

(33) of the Issacharites, men who knew how to interpret the signs of the times, to determine how Israel should act; their chiefs were 200, and all their kinsmen followed them;

תרגום דברי הימים א י״ב:ל״ג

(לג) וּמִן בְּנֵי יִשָשכָר יָדְעֵי סוּכְלְתָנוּ לְעִדָנַיָא חַכִּימִין לְמִקְבַע רֵישֵׁי שְׁגִין וְרֵישֵׁי יַרְחִין וּלְעַבָּרָא יַרְחַיָא וּשְׁנַיָא סוֹפִיסְטִין בְּמוֹלָדָא דְסִיהֲרָא לְמִקְבַּע מוֹעֲדַיָא בְּעִדַנְהוֹן בְּקִיאִין בִּתְקוּפָתָא דְשִׁמְשָׁא אִצְרוֹלוֹגִין (ס"א אִצְטְרוֹלוֹגִין) בְּמַזָלַיָא וְכוֹכְבַיָא לְמִידַע מָה כַשְׁרִין לְמֶעְבַּד בֵּית יִשְרָאֵל רַבָּנֵיהוֹן רֵישֵׁי סַנֶדְרִיָא מָאתָן כָּל אֲחוּהוֹן עַבְדִין פִּתְגָמֵי אוֹרַיְתָא וְחַכִּימִין עַל מֵימַר פּוּמְהוֹן:

Targum of I Chronicles 12:33

...

Translation: And from the sons of Issachar who are familiar with the science of astronomical time; they possess the knowledge of determining the new year, the new month, how to intercalate the months and the years; professors of the lunar conjuction (necessary for ) calculating the holidays in their proper time, expert in calculating the seasons of the sun, Astronomers, familliar with the movements of the Sun, the Moon, the stars, in order to determin what is fit for the house of Israel to do (agriculturally, (They are ) their Rabbis, the leaders of the Sanhedrin, 200 in number, and all their brothers fulfill the words of teh Torah, and become wise from the words of their mouths.

The wisdom of the movements of the stars and planets, which we possess, and utilies for our Jewish calendar is the wisdom which the Torah refers to in Devarim 4.

Q. #2 - From whence do we know that it is an actual mitzvah to study astronomy, and to calculate the Jewish calendar?

שבת ע״ה א:ב׳

אָמַר רַב זוּטְרָא בַּר טוֹבִיָּה אָמַר רַב: הַמּוֹתֵחַ חוּט שֶׁל תְּפִירָה בְּשַׁבָּת — חַיָּיב חַטָּאת, וְהַלּוֹמֵד דָּבָר אֶחָד מִן הַמָּגוֹשׁ — חַיָּיב מִיתָה, וְהַיּוֹדֵעַ לְחַשֵּׁב תְּקוּפוֹת וּמַזָּלוֹת וְאֵינוֹ מְחַשֵּׁב — אָסוּר לְסַפֵּר הֵימֶנּוּ.

Shabbat 75a:2

Rav Zutra bar Toviya said that Rav said: One who tightens the thread of a stitch on Shabbat is liable to bring a sin-offering. If two parts of a garment that were sewn together begin to separate, and one pulls the thread to reattach them, it is tantamount to having sewn them. The Gemara cites additional halakhot cited by Rav Zutra in the name of Rav. And one who learns even one matter from a magosh, a Persian priest, is liable to receive the death penalty. And one who knows how to calculate astronomical seasons and the movement of constellations, and does not do so, one may not speak with him because his actions are improper.

שבת ע״ה א:ד׳

אָמַר רַבִּי שִׁמְעוֹן בֶּן פַּזִּי, אָמַר רַבִּי יְהוֹשֻׁעַ בֶּן לֵוִי מִשּׁוּם בַּר קַפָּרָא: כָּל הַיּוֹדֵעַ לְחַשֵּׁב בִּתְקוּפוֹת וּמַזָּלוֹת וְאֵינוֹ מְחַשֵּׁב, עָלָיו הַכָּתוּב אוֹמֵר: ״וְאֵת פֹּעַל ה׳ לֹא יַבִּיטוּ וּמַעֲשֵׂה יָדָיו לֹא רָאוּ״. אָמַר רַבִּי שְׁמוּאֵל בַּר נַחְמָנִי אָמַר רַבִּי יוֹחָנָן: מִנַּיִן שֶׁמִּצְוָה עַל הָאָדָם לְחַשֵּׁב תְּקוּפוֹת וּמַזָּלוֹת — שֶׁנֶּאֱמַר: ״וּשְׁמַרְתֶּם וַעֲשִׂיתֶם כִּי הִיא חׇכְמַתְכֶם וּבִינַתְכֶם לְעֵינֵי הָעַמִּים״, אֵיזוֹ חָכְמָה וּבִינָה שֶׁהִיא לְעֵינֵי הָעַמִּים — הֱוֵי אוֹמֵר: זֶה חִישּׁוּב תְּקוּפוֹת וּמַזָּלוֹת.

Shabbat 75a:4

Rabbi Shimon ben Pazi said that Rabbi Yehoshua ben Levi said in the name of bar Kappara: Anyone who knows how to calculate astronomical seasons and the movement of constellations and does not do so, the verse says about him: “They do not take notice of the work of God, and they do not see His handiwork” (Isaiah 5:12). And Rabbi Shmuel bar Naḥmani said that Rabbi Yoḥanan said: From where is it derived that there is a mitzva incumbent upon a person to calculate astronomical seasons and the movement of constellations? As it was stated: “And you shall guard and perform, for it is your wisdom and understanding in the eyes of the nations” (Deuteronomy 4:6). What wisdom and understanding is there in the Torah that is in the eyes of the nations, i.e., appreciated and recognized by all? You must say: This is the calculation of astronomical seasons and the movement of constellations, as the calculation of experts is witnessed by all.

לעיני העמים - שחכמה הניכרת היא שמראה להם סימן לדבריו בהילוך החמה והמזלו' שמעידין כדבריו שאומר שנה זו גשומה והיא כן שנה זו שחונה והיא כן שכל העיתים לפי מהלך החמה במזלותיה ומולדותיה במזל תלוי הכל לפי השעה המתחלת לשמש בכניסת החמה למזל:

Translation:

In the eyes of the nations: For this is a demosstrable science for it shows them a proof of their words through the motions of the sun and the constellations, when they say this year will be abundant in rain, or that year will be overly hot (i.e. a year of drought), and it will prove to be so for all the seasons follow the motions of the sun and the constelations, and depend on the sun's conjunction with the stars of the Zodiac according to the proper hour in which the sun enters the constellation

Aries - טלה

Taurus - שור

Gemini - תאומים

Cancer - סרטן

Leo - אריה

Virgo - בתולה

Libra - מאזנים

Scorpio - עקרב

Sagitarius - קשת

Capricorn - גדי

Aquarius - דלי

Pisces - דגים

Mnemonic:

טש"ת סא"ב מע"ק גד"ד

איוב ט׳:ט׳

(ט) עֹֽשֶׂה־עָ֭שׁ כְּסִ֥יל וְכִימָ֗ה וְחַדְרֵ֥י תֵמָֽן׃

Job 9:9

(9) Who made the Bear and Orion, Pleiades, and the chambers of the south wind;

אבן עזרא על איוב ט׳:ט׳:א׳

(א) עש - הם שבעה כוכבים: כסיל וכימה. שני כוכבים גדולים האחד בפאת שמאל מגלגל הנוטה והשני בפאת נגב, ועש בפאת צפון הגלגל הגדול.

Ibn Ezra on Job 9:9:1

...

ישעיהו י״ג:י׳

(י) כִּֽי־כוֹכְבֵ֤י הַשָּׁמַ֙יִם֙ וּכְסִ֣ילֵיהֶ֔ם לֹ֥א יָהֵ֖לּוּ אוֹרָ֑ם חָשַׁ֤ךְ הַשֶּׁ֙מֶשׁ֙ בְּצֵאת֔וֹ וְיָרֵ֖חַ לֹֽא־יַגִּ֥יהַ אוֹרֽוֹ׃

Isaiah 13:10

(10) The stars and constellations of heaven Shall not give off their light; The sun shall be dark when it rises, And the moon shall diffuse no glow.

אבן עזרא על ישעיהו י״ג:י׳:א׳

(א) כי. וכסיליהם. יש אומרים כי כסיל הוא הכוכב שהוא קרוב מהסדן הדרומי שימותו הגמלים אם יראוהו, ולפי דעתי שהוא לב עקרב, ויתכן להיות הכסילים מגזרת הכסלים (ויקרא ג' ד') שהם קרובים אל הסדנים, ויאמר רבי יונה כי כסיל הוא אחד וחבר כוכבים אחרים אליו וכמוהו בתי השן (עמוס ג' ט"ו):

Ibn Ezra on Isaiah 13:10:1

(1) וכסיליהם According to some, כְּסִיל is the name of the star which is nearest to the south pole, at the sight of which the camels die.¹¹The star near the south pole is seen by the inhabitants of the northern hemisphere only in the midst of the summer, when the camels are exposed to the greatest heat. The name of the star is, according to I. E. (on Amos 5:8) Edom in Hebrew, Sahil in Arabic; it is now known by the name Kanopus. My opinion is¹²Concerning the four constellations mentioned in the Bible חַדְרֵי תֵימׇן עׇשׁ כְּסִיל כִּימׇה (Amos 5:4, Job 9:9, 38:31), I. E. gives the following explanation: חדרי תימן Kanopus and the stars round him; עש the Great Bear; כסיל the Heart of the Scorpion; כימה the left eye of the Taurus. (In his Kele Nehosheth, a description of an astronomical instrument and its use, כימה is identified with Algadia, or the Haedi in the Auriga.) These four constellations occupy, according to I. E. the four most important spots of the celestial sphere; namely, עש is near the north pole; חדרי תימן near the south pole; כסיל near the south equinoctial point; כימה near the north equinoctial point. At present, however, the latter two are not near the mentioned points, because of the eastward motion of the Zodiac, which amounts in a hundred years nearly to one degree and a half. that כסיל is the Heart of the Scorpion constellation; it is, however, possible that כסילים in this verse—comp. כְּסׇלִים flanks (Lev. 3:4)—signifies the stars near the poles.¹³This derivation is also mentioned, and, as it seems, adopted by I. E. in his commentary on Lev. (3:4.) A distinction is therefore to be made between the singular כסיל the Heart of the Scorpion, and the plural כסילים the stars on the sides or flanks of the two poles, hinted at in the dual form of the preceding שׇׁמַיׅם. (Comp. I. E., Sefer hashem, 100:1.) R. Jonah remarks that there is only one star named כסיל, and that here, in the plural כסילים, other stars are included; comp. בתי השן the houses of ivory (Am. 3:15).¹⁴R. Jonah is here not censured so severely as in the commentary on Amos 4:15. I. E. says there—of course only for the sake of a play of words, in which he frequently indulges, not with the intention to offend—הוא בשמים רבים הם בארץ והוא אחד מהם אם כסיל אחד. R. Jonah thinks that there was only one house of ivory in the days of Amos, namely the one built by king Ahab (1 Kings 22:39), because no mention is made of any other such house. The plural בתי השן houses of ivory must, according to his opinion, include houses which were not of ivory. This opinion is justly—though too harshly—rejected by I. E.

In May of 1488, Bartolomeo Dias, a Potuguese explorer , discovered the Cape of Good Hope. He Also discovered the constelations of the southern hemisphere. He claimed to have discovered the fabled constelation of the Southern Anvil , which can kill a Camel when it appears. He renamed it the consellation Mensa. The Sefaria translater decided that it is the South Pole, which certainly would kill a Camel

The ecliptic is an imaginary line on the sky that marks the annual path of the sun. It is the projection of Earth's orbit onto the celestial sphere. ... Besides define the path of the sun, the ecliptic marks the line along which eclipses occur, the moon and planets and asteroids wander, the Zodiac constellations live.

רש"י על משלי ג׳:ט׳:א׳

מהונך. מכל מה שחננך אפי' מקול ערב (אל תקרי מהונך אלא מגרונך):

Rashi on Proverbs 3:9:1

From your wealth (mehonkha): From all that He graced you with, even from a pleasant voice (do not read it as mehonkha [from your wealth] but [rather] as megaronkha [from your voice]).