(יט) וּפֶן־תִּשָּׂ֨א עֵינֶ֜יךָ הַשָּׁמַ֗יְמָה וְֽ֠רָאִיתָ אֶת־הַשֶּׁ֨מֶשׁ וְאֶת־הַיָּרֵ֜חַ וְאֶת־הַכּֽוֹכָבִ֗ים כֹּ֚ל צְבָ֣א הַשָּׁמַ֔יִם וְנִדַּחְתָּ֛ וְהִשְׁתַּחֲוִ֥יתָ לָהֶ֖ם וַעֲבַדְתָּ֑ם אֲשֶׁ֨ר חָלַ֜ק ה' אֱלֹקֶ֙יךָ֙ אֹתָ֔ם לְכֹל֙ הָֽעַמִּ֔ים תַּ֖חַת כָּל־הַשָּׁמָֽיִם׃ (כ) וְאֶתְכֶם֙ לָקַ֣ח ה' וַיּוֹצִ֥א אֶתְכֶ֛ם מִכּ֥וּר הַבַּרְזֶ֖ל מִמִּצְרָ֑יִם לִהְי֥וֹת ל֛וֹ לְעַ֥ם נַחֲלָ֖ה כַּיּ֥וֹם הַזֶּֽה׃
(19) And when you look up to the sky and behold the sun and the moon and the stars, the whole heavenly host, you must not be lured into bowing down to them or serving them. These the LORD your God allotted to other peoples everywhere under heaven; (20) but you the LORD took and brought out of Egypt, that iron blast furnace, to be His very own people, as is now the case.
אִיתְּמַר, רַבִּי חֲנִינָא אוֹמֵר: מַזָּל מַחְכִּים, מַזָּל מַעֲשִׁיר, וְיֵשׁ מַזָּל לְיִשְׂרָאֵל. רַבִּי יוֹחָנָן אָמַר: אֵין מַזָּל לְיִשְׂרָאֵל. וְאַזְדָּא רַבִּי יוֹחָנָן לְטַעְמֵיהּ, דְּאָמַר רַבִּי יוֹחָנָן: מִנַּיִין שֶׁאֵין מַזָּל לְיִשְׂרָאֵל? שֶׁנֶּאֱמַר: ״כֹּה אָמַר ה׳ אֶל דֶּרֶךְ הַגּוֹיִם אַל תִּלְמָדוּ וּמֵאוֹתוֹת הַשָּׁמַיִם אַל תֵּחָתּוּ כִּי יֵחַתּוּ הַגּוֹיִם מֵהֵמָּה״ — הֵם יֵחַתּוּ, וְלֹא יִשְׂרָאֵל.
It was stated that Rabbi Ḥanina says: A constellation makes one wise and a constellation makes one wealthy, and there is a constellation for the Jewish people that influences them. Rabbi Yoḥanan said: There is no constellation for the Jewish people. And Rabbi Yoḥanan follows his own reasoning, as Rabbi Yoḥanan said: From where is it derived that there is no constellation for the Jewish people? As it is stated: “Thus said the Lord: Learn not the way of the nations, and be not dismayed at the signs of heaven; for the nations are dismayed at them” (Jeremiah 10:2). The nations will be dismayed by them, but not the Jewish people.
Nachmanides (13th cent. Spain) - Responsum 282
The study of astrology is not forbidden. Even though the Talmud (Shabbat 156a) states: “There is no mazal (celestial, source of influence) for Israel,” there were sages who did not share that view. Thus, even though the latter was a minority opinion, the fact that it exists demonstrates that astrology is not nonsense, nor is involvement in its study forbidden.
(ח) אֵיזֶהוּ מְעוֹנֵן אֵלּוּ נוֹתְנֵי עִתִּים שֶׁאוֹמְרִים בְּאִצְטַגְנִינוּת יוֹם פְּלוֹנִי טוֹב יוֹם פְּלוֹנִי רַע יוֹם פְּלוֹנִי רָאוּי לַעֲשׂוֹת בּוֹ מְלָאכָה פְּלוֹנִית שָׁנָה פְּלוֹנִית אוֹ חֹדֶשׁ פְּלוֹנִי רַע לְדָבָר פְּלוֹנִי:
(ט) אָסוּר לְעוֹנֵן אַף עַל פִּי שֶׁלֹּא עָשָׂה מַעֲשֶׂה אֶלָּא הוֹדִיעַ אוֹתָן הַכְּזָבִים שֶׁהַכְּסִילִים מְדַמִּין שֶׁהֵן דִּבְרֵי אֱמֶת וְדִבְרֵי חֲכָמִים. וְכָל הָעוֹשֶׂה מִפְּנֵי הָאִצְטַגְנִינוּת וְכִוֵּן מְלַאכְתּוֹ אוֹ הֲלִיכָתוֹ בְּאוֹתוֹ הָעֵת שֶׁקָּבְעוּ הֹבְרֵי שָׁמַיִם הֲרֵי זֶה לוֹקֶה שֶׁנֶּאֱמַר (ויקרא יט כו) "לֹא תְעוֹנֵנוּ". וְכֵן הָאוֹחֵז אֶת הָעֵינַיִם וּמְדַמֶּה בִּפְנֵי הָרוֹאִים שֶׁעוֹשֶׂה מַעֲשֵׂה תִּמָּהוֹן וְהוּא לֹא עָשָׂה הֲרֵי זֶה בִּכְלַל מְעוֹנֵן וְלוֹקֶה:
(8) Who is an observer of times (soothsayer)? They that point at times, saying astrologically: "That day is a good one, that day is a bad one; that day is fit to do that particular work, but that year, or that month, is bad for that particular thing.11
(9) It is forbidden to be an observer of times, though no act be committed, save to make known the lies to such fools who believe them to be true speech of the wise. Moreover, he who does aught because of the signs of astrology, and times to do his work or go on his mission on the very time, set by the heaven-gazers, even he is striped, for it is said: "Nor observe times" (Lev. 126).12Here a distinction must be made between an observer of times and an enchanter. See supra, Par. 7. G. Likewise, one who deludes the eyes by performing some act alleging it to be wonderful, but in truth makes no performance at all, even he is included among observers of time, and his punishment is stripes.
(א) שלא לכשף לעונן ולנחש. ובו י"ט סעיפים:
אין שואלין בחוזים בכוכבים ולא בגורלות: הגה משום שנאמר תמים תהיה עם ה' אלקיך (ב"י בשם תוספות דע"פ ובשם ספרי) וכ"ש דאסור לשאול בקוסמים ומנחשים ובמכשפים (פסקי מהרא"י סי' צ"ו):
(ב) נהגו שאין מתחילין בב' ובד' ואין נושאין נשים אלא במילוי הלבנה: הגה ולכן נהגו ג"כ להתחיל ללמוד בר"ח כי אע"פ שאין ניחוש יש סימן (סמ"ק סימן קל"ו) במה שאדם יודע שהוא כנגד המזל לא יעשה ולא יסמוך על הנס אלא שאין לחקור אחר זה משום תמים תהיה (תשובת רמב"ן סימן רפ"ו) כמו שנתבאר:
1. That one should not perform sorcery, soothsaying, or divination.
One should not consult with stargazers or those who cast lots. Rema: Because as it says you shall be simple with the Lord your God. And all the more so it is forbidden to consult with magicians, diviners, and sorcerers.
2. We have the custom not to begin something on Monday or Wednesday and women only marry when the moon is waxing (the first half of the month). Rema: And we also have the practice to begin studying on Rosh Chodesh, because even though it is not divination, there is a sign. What a person knows is against the stars he will not do, and we do not rely upon miracles. Rather, we don't deeply investigate this (astrology) because of "you shall be simple," as was explained.