May a Jew Believe in Astrology?

An earlier version of the following essay was presented at Congregation Beth Aaron, Teaneck, NJ, on the second day of Shavuot (5/28/12):

Introduction:
I will begin by defining the topic: "Astrology" refers to any belief or practice based on the idea that heavenly objects influence human affairs. The idea likely originated in the very early stages of civilization.  Astrology was widespread in the ancient and medieval worlds and, for reasons we will soon address, remains popular in segments of secular Western society.  The central thesis of astrology is straightforward: It is possible to explain the past, and to predict the future, from the positions of the planets among the fixed stars. Astrologers operate in a solar system consisting of seven "planets": The Sun, the Moon, and the five true planets visible to the naked eye (Mercury, Venus, Mars, Jupiter, and Saturn).  Until the seventeenth century, these seven bodies, as well as the stars, were thought to orbit the Earth.

In this model, stars are called “fixed” because their positions relative to each other appear constant, while planets (from the Greek word for "wanderers") move perceptibly over time against the background of the fixed stars.  For astrologers -- really, for anyone observing the planets -- the most significant constellations on the celestial sphere are the set of twelve known as the zodiac.  These twelve groups of stars are especially noteworthy because the "planets," including the Sun and the Moon, appear to travel through them, near an imaginary line called the ecliptic.  The area of the sky where the planets move was divided into twelve sections, as there are roughly twelve lunar months in a solar year.  The Sun appears to spend about a month in each of twelve constellations of the zodiac. For example, the month known as Adar on the Hebrew calendar was, at one time, the approximate month in which the Sun resided in Pisces, the fish (for reasons that are not directly relevant here, this is no longer the case).  It is important to emphasize that there is absolutely no inherent significance to the shapes of these constellations; for no reason other than convenience, they were grouped artificially by ancient people into shapes suggesting familiar animals, mythological creatures, or common objects.  From the Mayans to the ancient Chinese, ancient cultures around the world imagined vastly different objects within the zodiac.

Astrology should not be confused with astronomy.  Astronomers study planets, stars, and other objects in the sky.  Within the bounds of their astronomical work, modern astronomers and astrophysicists are expected not to speculate on the metaphysical impact these objects may or may not have on humanity.  However, this was not always so. The distinction between astronomy and astrology was often blurry; much like chemistry and alchemy, the two endeavors coexisted and were often indistinguishable for much of human history.  But, like alchemy, the scientific community has for several centuries considered astrology a completely unscientific discipline; in other words, pseudoscience rather than science. But note that although many beliefs are considered pseudoscientific, they are not equivalent. Philosophically and historically, astrology should not be placed in the same category as, say, believing in alien abductions or in the mystical power of crystals and pyramids.  In fact, as I will show, it was quite reasonable for ancient people to embrace an astrological worldview and to believe wholeheartedly, for example, that it was critical to know the position of Mars in the zodiac before going into battle, or that a particular day on the calendar was ideal to begin construction on a new house.  

So, what motivated (and continues to motivate) humans to believe in astrology? Generally, its origins are in one or more of three types of ideas:

The first, which is likely closest to its historical origins, may be called mythological or religious.  To the ancients, the planets were gods or closely associated with the gods (hence the planet names we all use), and deeply involved in human affairs.  This assumption was fairly logical to ancient people, considering their view of the Earth as the center of the cosmos.  Over time, however, animism and polytheism fell out of favor and were replaced by a more mechanistic model of the heavens.  This leads us to the second motivation, which can be considered naturalistic or “scientific.”  

It is undeniable that the stars and planets have an impact on human life, though not in the same way imagined by astrologers.  All ancient people knew, for instance, that the seasons were related to the position of the Sun in the zodiac and to the rising and setting of certain stars.  The entire agricultural calendar followed well-known astronomical cycles.  In ancient Egypt, for example, the appearance of Sirius (the “dog star”) just before sunrise indicated that the Nile would soon flood.  So, with a little imagination and a set of supposedly empirical observations, it was quite reasonable for ancient people to conclude that planetary configurations also dictate human life.  

The third category of ideas underlying astrology is psychological, and this is the primary motivation for its modern adherents.  Humans naturally desire to maximize control over their lives. Understanding the causes of important events in nature and in daily life provides a heightened sense of control over one's environment.  It is much more comforting to blame natural or personal disasters on the stars than on unpredictable cosmic randomness, a concept foreign to ancient thinkers (Epicurus and Lucretius being noteable exceptions).  Astrology was -- and remains for many -- a seemingly objective system allowing humans to better understand themselves, explain the past, and, most importantly, to better manage future risk.

I will now clarify the question which makes up the title of the shiur: “May a Jew believe in Astrology?” was not posed as a halakhic question in the technical sense.  I will make no attempt at a comprehensive survey of halakhic authorities on the subject, and, of course, I am not here to offer pesak.  Rather, the title's question -- as well as its answer -- are primarily ideological.  Call this an exercise in haskhafah or mahshavah or, if you remain unconvinced, consider it merely my personal opinion.  I believe that this discussion will indeed point the way to a proper halakhic stance on the issue, but as a practical matter I will leave that to others.  

Now that I’ve defined the scope of the question, I will provide my answer up front and unequivocally:

The answer to the question, “May a Jew believe in astrology?” is an emphatic “No,” or, more precisely, “Absolutely not.”  I believe this should be the answer on the mind and lips of every twenty-first century ben Torah.  I have three complementary reasons for this conclusion.

First, and primarily, astrology is false.  Second, astrology undermines the fundamental moral and religious notions of freedom and human accountability.  And third, if we insist on the truth of astrology simply because of its presence in the Talmud, Midrash, and other Jewish texts, we damage Orthodoxy’s reputation in the eyes of our children and students, and in the eyes of those outside our community. I should add that I am not proposing much that is new; essentially, I am following Maimonides. But recent intellectual trends in the Orthodox community require that we restate Maimonides' position in a modern context.  

Again, my question and my answer do not belong to the realm of technical halakhah, in the way other issues do, such as the question of wearing tefillin on Hol Ha-Moed.  In such halakhic matters, there may be valid arguments on both sides.  Today’s discussion also does not belong to abstract philosophy or theology as in, for example, the conflict between Hasidism and Mitnagedism, where traditional Judaism tolerates conflicting ideologies. This is not the type of question which can be resolved by tallying rishonim and aharonim on either side of the issue, and then concluding with a pesak according to the majority view.  Nor does this topic lend itself to a conclusion that will leave us with a warm feeling of “elu va-elu divre elokim hayyim,” assigning equal weight in our minds to all, and even contradictory, opinions. These are not the approaches we should take with regard to astrology and other scientific errors.  To use an analogy, the discoveries of Galileo and Newton made it impossible to have a pluralistic view on what lies at the center of the solar system, the Sun or the Earth.  In the same way, the question of accepting astrology -- in theory and in practice -- is a question of reality; of “metzius.”  It revolves around the validity of astrology as a true science.  Now, for several centuries the scientific consensus has been that astrology is a pseudoscience rather than a true science; pseudoscience is bad science -- one could call it sheker -- masquerading as truth.  Midevar sheker tirhak: As bnei Torah, we must reject that which is false because it is false, and always pursue the truth.  So the question I have posed today is, at its core, a scientific matter.

I am not saying that one’s stance on astrology has no impact on their religious beliefs; quite the opposite is true, and that is why we are having this discussion today.  Astrology provides a cause-and-effect model of human behavior and therefore takes a particular moral view of man. Morality, of course, is a major concern of religion.  From a moral and religious viewpoint, astrology is extremely problematic, since it is by definition a deterministic and fatalistic theory of human behavior.  As such, it comes into direct conflict with some of the basic moral principles of Judaism and other Western religions; namely, free will (behira) and accountability for one’s actions (sekhar va-onesh).   As we will see from the sources, especially from the Talmud, Hazal struggled to reconcile these beliefs with astrological fatalism.

As modern rationalistic people, the only motivation we require to abandon astrology is the fact that it a false idea.  But in addition to that, astrology violates some of the most fundamental moral and religious ideas of Judaism. As we will see, that is basically the approach of the Rambam.  I would also argue that if we look carefully, the seeds of this approach are already visible in Hazal.

Torah and Prophets:
Within a long list of practices related to sorcery and divination, the Torah prohibits me’onen (Lev. 19:26; Deut. 18:14 [Sources 1,2]) .  This word is most commonly identified with astrology (KJV translates it as “an observer of times”).  Rashi on Deut. 18:14, citing the Talmud Sanhedrin 65b, offers two explanations for me’onen: The first, taking ayin, or eye, as the root of the word, is ahizat enayim, some sort of magic or sleight of hand.  The second is astrological divination, which assumes that me’onen derives from the word onah, or time.  Rambam in Hil. Akum includes both definitions.  Ibn Ezra does not accept the identification of me’onen with astrology; instead, reading the word as a derivative of 'anan (cloud), he defines it as cloud divination.  This is not too surprising, considering that Ibn Ezra was himself a professional astrologer.  Now, why does the Torah prohibit me’onen and other forms of sorcery?  The Torah itself answers this question: tamim tiheyeh in Hasehm elokekhah - one’s faith must be perfect or whole, that is, not shared with occult sources of knowledge.  But does that mean that this knowledge is real and true, just that it is prohibited?  This is not entirely clear from the verses themselves, but Maimonides insisted that such idolatrous beliefs and practices are prohibited because they are false.

During the biblical period, astrology was often deeply intertwined with paganism in the form of astral religion. As noted earlier, the planets were associated with gods; one worshipped Venus or Jupiter or Saturn when it was thought to be beneficial to do so.  Like Deuteronomy, the Prophets railed against the practice of divining the future from the stars [Sources 3, 4].  Even if the astrology of the Tanakh was not directly associated with pagan ritual, it was still perceived as deeply associated with the cultures of neighboring nations, and Israel was warned against participating in these activities.  Ki lo nahash be-yaakov - Israel, unlike her neighbors, was to rely only on God and the prophets.  

Talmud and Midrash:
There are numerous references to astrology in the literature of Hazal, and this shows how pervasive the belief was in the ancient world.  There is no doubt that Hazal -- along with most rational people of that period -- believed that it was a real cosmic force.  It also appears that due to a new cultural reality having to do with the spread of Hellenism throughout the Near East, astrology was seen as a natural phenomenon unrelated to paganism.  So unlike the Prophets, the Sages did not object to it as a foreign or dangerous discipline.

[Source 5: Shabbat 156]:
This famous sugya discusses in detail how astrology may or may not influence one’s destiny.  It is important to emphasize that the Talmud never doubts that astrology is real.  In the first part of the passage, (not included in the sources) there is a detailed debate about the influence of the sign of the day vs. the sign of the hour in which one was born.  The gemara then takes a different approach and tries to demonstrate that Israel is immune to astrological influence.  This is the notion of ein mazal le-yisrael (EML). But in the literature of the Sages, astrology is not rejected as a foolish pursuit.

Two important notes on this passage: First, note its structure.  There is not a single proof quoted here in favor of the yesh mazal le-yisrael position; this likely indicates that it was the more popular view.  For EML, however, the gemara cites fully five different arguments for support, using biblical proof-texts and anecdotes related to various Sages.  The fact that the sugya concludes with this argument shows that this was the position of the Talmudic editors, and the citation of so many proofs means that they were struggling against a very popular belief.  Note that the authorities cited here are no mediocre figures -- in fact, this is an A-list of tannaim and amoraim from a variety of historical periods: R. Akiva; Rav; Shmuel (who was considered an astronomical expert); R. Yohanan; R. Nahman bar Yitzhak.  Second, EML does not mean that astrology is false; it only rejects astrology with respect to the destiny of the Jewish people.  Hazal struggled with the fact that astrology contradicted behira and moral accountability, so they endeavored to demonstrate that Israel was immune from the power of the stars and planets.  Today, however, we know that astrology false.  So, I believe that had this sugya been written today, instead of ein mazal le-yisrael, the gemara would have simply dismissed the whole problem. Perhaps they would have pronounced, more fundamentally, "ein mazal."

Ibn Ezra and Maimonides:
We now continue on to the medieval period.  Astrology was widespread in Christian and Muslim medieval Europe.  Several Jewish medieval authorities utilized astrological concepts within their biblical commentaries and philosophical writings.  Ibn Ezra, who was born in Spain in the eleventh century and spent his life moving through various European cities, was the greatest of all Jewish astrologers.  He wrote numerous books on the subject, some of which remain in manuscript.  A few were translated into Latin and French and became popular astrological texts in medieval Europe.  

On the subject of astrology in medieval Jewish thought, there is no better contrast to the Ibn Ezra than Maimonides, who was his near contemporary (Ibn Ezra was about fifty years older).  As mentioned, the Rambam forcefully maintained that the Torah prohibited astrology because it is false.  There is little doubt that he was polemicizing against a very widespread and popular belief [Source 6: Letter on Astrology].  In the letter, he addresses a concern that continues to trouble bnei Torah today:  How can we account for all the passages in Hazal that refer to astrology as a real phenomenon?  He offers three different answers to this question:  

1. Although the Talmud may entertain other views, it concludes its discussion of the matter by rejecting astrology (he is likely referring to our sugya from Shabbat).
2. In general, one must not reject reason due to a mistaken view among a minority of the Sages.
3. Like many verses in the Bible, the astrological references of the Sages may have been metaphorical or stated out of a temporary necessity, but they did not truly believe in astrology.

The Rambam’s ideological position on astrology translated directly into his halakhic position [Source 7: MT, Akum 11].  He states unequivocally that astrology is a form of idolatry that is prohibited by the Torah.  It is not prohibited because it taps into some kind of sinister but effective koah ha-tum’ah or “dark art.”  Rather, the Rambam states repeatedly and emphatically that astrology and other idolatrous practices are prohibited because they are false.  When the Torah says tamim tehiyeh it means that one must rely completely on reason and intellect.  Neglect of reason, for the Rambam, leads to the sin of idolatry.

Aside from calling it “stupidity,” the Rambam highlighted astrology’s conflict with a fundamental principle of Judaism, freedom and accountability [source 8, Hil. Teshuva].  Astrological determinism leaves no room for the whole program of Torah and mitzvot.  Free will becomes impossible, as does reward and punishment.  

The final passage from Maimonides [source 9], which is chronologically the earliest, comes from his Commentary on the Mishnah, Introduction to Perek Helek.  The Rambam is here speaking generally about different views of the aggadot of Hazal, especially those which appear improbable or strange.  He describes three categories of people, in terms of how they approach these midrashim.  The first group takes all midrashim literally and insists on their plausibility.  The second (here he is likely speaking of the Karaites) also takes a literalist approach but instead of praising Hazal, they ridicule them for espousing nonsense that contradicts reason.  The third group argues that Hazal never intended these stories literally, and its members assign them an allegorical or symbolic interpretation that does not contradict reason.

In describing the first group, the Rambam emphasizes the reputational harm they do to Judaism.  He notes in irony that the honor they seek to give to Hazal results in their humiliation.  The reputational consequences of Jewish belief was important to the Rambam, as it should be for us.  

In summary, the Rambam’s objections to astrology include two major themes. The third is implied by his general objections to those who misrepresent the aggadot of the Sages.  I include it here due to its current relevance:

1. Astrology is false, and therefore prohibited
2. Astrology contradicts the fundamental Jewish principles of free will and moral accountability
3. Those Jews who insist on the truth of apparently false ideas in the Talmud leave a negative impression of Judaism in the eyes of its observers

Shulhan Arukh:
There are two short paragraphs here on astrology [source 10].  In the first, the Mehaber prohibits seeking the advice of astrologers.  At the same time, in the second, he approvingly cites two customs based on astrology (compare, e.g., to his view of kaparot, which he rejects).  We certainly could not imagine Maimonides citing these customs in the Mishneh Torah (in fact, Maimonides omits scores of halakhot and minhagim found in the Talmud, which he believed to be based on superstition).  Most likely, then, R. Joseph Karo considered astrology a real, if prohibited, discipline.

The Rema’s position, based on a teshuvah attributed to Ramban, adds a new dimension to the discussion.  We are prohibited from pro-actively seeking the counsel of astrologers, due to the concept of tamim tehiyeh.  But if, somehow, one already has obtained a negative astrological prediction, he must not ignore it, due to ein somekhin al ha-nes.  The Rema clearly felt that astrology was a force to be reckoned with.  We can use an analogy from modern medicine: For the Ramban, going to battle on an astrologically inauspicious day would be as reckless a move in his eyes as, in our own eyes, a person with a strong family history of heart disease taking up smoking, maintaining a high fat and sodium-rich diet, and refusing to exercise.  Both examples, each in its own context, disregard what is perceived as reality.  To throw caution to the wind and ignore it, Ramban says, would be halakhically irresponsible.

 
Conclusion:
Several years ago, I mentioned to a prominent Orthodox rabbi that I had recently taught a class on the place of Astrology in Judaism.  His reaction was unexpected: He said that the presence of astrology in Jewish literature is embarrassing, and that it should not be publicized.

I have a different view.  Whether astrology, or any superstitious idea within Judaism, is cause for embarrassment depends on how it is approached and how it is presented.  If, when we encounter an astrological belief in Hazal, we “cast reason behind us” -- in the words of the Rambam -- and present astrology as a legitimate part of Torah then, I believe, we have indeed placed traditional Judaism in an embarrassing light.  Again, to paraphrase the Rambam, if by attempting to honor Hazal or to strengthen their authority, we insist that every belief in the Talmud is true, even those regarding nature and science then, ironically, we humiliate Hazal and humiliate contemporary Orthodoxy.  It is critically important that Orthodox Judaism be viewed with admiration, both within Jewish society -- beginning with our own children and students -- and from the outside.  We must not allow our beliefs and traditions to be ridiculed as medieval obscurantism.  Such an approach may leave the impression, with us and our neighbors, has ve-shalom, of  רק עם סכל ונבל הגוי הקטן הזה  instead of  רַק עַם חָכָם וְנָבוֹן הַגּוֹי הַגָּדוֹל הַזֶּה .

If, on the other hand, we approach this topic from an historical perspective, which places astrology in its proper ideological and cultural context, it need not be embarrassing.  I would argue just the opposite position: As the intellectual heirs of Hazal, their references to astrology should be a source of pride.  Like us, Hazal were very aware of and engaged with many cultures and ideologies.  They operated in a diverse marketplace of ideas.  In the case of astrology, they struggled to reconcile the principle of human freedom inherent in the Torah with astrological determinism, an idea included in the best science of their day.  They could not dismiss astrology out of hand; for them, it would be denying reality.  At the time, virtually everyone, including the most knowledgeable and “scientific” people within society, believed that the stars and planets had much to do with the details of human life, and they were convinced they had empirical proof for this belief.  But for us, thankfully, the Talmud’s struggle with the assumed efficacy of astrology no longer exists.  Maintaining this struggle today is the result of either ignorance, misplaced piety, or some combination of both.

Now, Maimonides was virtually alone among medieval Jewish thinkers in rejecting astrology as nonsense and thus precluding any halakhic validity to astrological theory or practice.  Some may insist that his opinion is a da’at yahid; a single, minority opinion among many opposing opinions.  In fact, Shulhan Arukh (especially the Rema) does not follow Maimonides.  But I believe we should take a different approach.  I believe that our perspective as modern bnei Torah on this and similar issues should be very close to that of the Rambam, and not only because he was the Rambam, but because he got this right!  

The dispute between Maimonides and other medieval authorities with regard to astrology is essentially a “mahalokes in metzius” - a dispute about reality rather than Halakha. Those -- like Nahmanides and Rema -- who insisted that one must take his mazal into consideration and not rely on miracles, were convinced that one’s astrological predisposition to misfortune was real.  But, when a new reality emerges -- that astrology has no basis in fact -- then it is contrary to both reason and Judaism to attribute it any validity.  I believe that if all the Sages quoted in the passage in Shabbat, as well as Rashi, Ramban, Ibn Ezra, Ralbag, Rabbenu Bahya, and other medieval proponents of astrology were sitting here today, each one would stand up before us and admit that astrology is false and therefore not worthy of our attention or concern.

The third theme of the Maimonides, regarding the reputational hazards of false beliefs, is also critically important, today as much as ever.  We do not enhance the reputation of Hazal or the Talmud or Orthodoxy by promoting, in the name of fealty to tradition, obsolete ideas that appear in our religious texts.  I am not saying that we must be apologetic about the Talmud, Midrash, or our traditions in general.  Yet our perception le-enei ha-amim -- which begins with our self-perception -- remains critically important, as it was for Maimonides.  We must do everything we can to prevent the deterioration of our image, within our community and without, from that of an  עַם חָכָם וְנָבוֹן to one of an עם סכל ונבל.

Much of the discussion today might be considered negative, as I have focused on debunking a popular belief rather than offering a set of new ideas.  But I think there is also a very positive message here, one that deserves much fuller treatment in the future.  The message is that as educators and parents, we must show our students, children, and peers the beauty and the truth of our texts, traditions, and beliefs, their compatibility with a modern, twenty-first century worldview, and the profound wisdom and ethical sensitivity of our greatest thinkers over the centuries.  The wisdom and beauty of their teachings may, unfortunately, be drowned out by the shrill voices of our time, if we allow those voices to set the tone and the agenda for Orthodox thought.  

I do not claim that the approach I outlined today is the only legitimate one, but I do believe it is the best one.  I also believe that it is the type of approach to the interplay of tradition and the changing realities of modern life in which our community can take much pride.

Source Texts:

1. ויקרא פרק יט פסוק כו

לֹא תֹאכְלוּ עַל הַדָּם לֹא תְנַחֲשׁוּ וְלֹא תְעוֹנֵנוּ:

סנהדרין סה: - וחכמים אומרים: זה האוחז את העינים. רבי עקיבא אומר: זה המחשב עתים ושעות, ואומר: היום יפה לצאת, למחר יפה ליקח, לימודי ערבי שביעיות חיטין יפות, עיקורי קטניות מהיות רעות.

רש"י ויקרא שם: ולא תעוננו - לשון עונות ושעות, שאומר יום פלוני יפה להתחיל מלאכה, שעה פלונית קשה לצאת:

אבן עזרא: תעוננו - והנכון בעיני מגזרת ענן, כי ידוע כי יש מי שיעונן שיסתכל בעננים ובדמותם ובתנועתם.

2. דברים פרק יח

(י) לֹא יִמָּצֵא בְךָ מַעֲבִיר בְּנוֹ וּבִתּוֹ בָּאֵשׁ קֹסֵם קְסָמִים מְעוֹנֵן וּמְנַחֵשׁ וּמְכַשֵּׁף:. . .  (יג) תָּמִים תִּהְיֶה עִם יְקֹוָק אֱלֹהֶיךָ :(יד) כִּי הַגּוֹיִם הָאֵלֶּה אֲשֶׁר אַתָּה יוֹרֵשׁ אוֹתָם אֶל מְעֹנְנִים וְאֶל קֹסְמִים יִשְׁמָעוּ וְאַתָּה לֹא כֵן נָתַן לְךָ יְקֹוָק א-ֱלֹהֶיךָ:

רש"י: מעונן - רבי עקיבא אומר אלו נותני עונות, שאומרים עונה פלונית יפה להתחיל. וחכמים אומרים אלו אוחזי העינים:

3. ישעיהו פרק מז

(יב) עִמְדִי נָא בַחֲבָרַיִךְ וּבְרֹב כְּשָׁפַיִךְ בַּאֲשֶׁר יָגַעַתְּ מִנְּעוּרָיִךְ אוּלַי תּוּכְלִי הוֹעִיל אוּלַי תַּעֲרוֹצִי: (יג) נִלְאֵית בְּרֹב עֲצָתָיִךְ יַעַמְדוּ נָא וְיוֹשִׁיעֻךְ הֹבְרֵי שָׁמַיִם הַחֹזִים בַּכּוֹכָבִים מוֹדִיעִם לֶחֳדָשִׁים מֵאֲשֶׁר יָבֹאוּ עָלָיִךְ:

You are helpless, despite all your art. Let them stand up and help you now, the scanners of the heavens, the star-gazers, who announce, month by month, whatever will come upon you.

4. ירמיהו י:ב

כֹּה אָמַר יְקֹוָק אֶל דֶּרֶךְ הַגּוֹיִם אַל תִּלְמָדוּ וּמֵאֹתוֹת הַשָּׁמַיִם אַל תֵּחָתּוּ כִּי יֵחַתּוּ הַגּוֹיִם מֵהֵמָּה:

Thus said the Lord: Do not learn to go the way of the nations, and do not be dismayed by portents in the sky; let the nations be dismayed by them!

5. תלמוד בבלי מסכת שבת דף קנו עמוד א-ב

איתמר, רבי חנינא אומר: מזל מחכים, מזל מעשיר, ויש מזל לישראל. רבי יוחנן אמר: אין מזל לישראל. ואזדא רבי יוחנן לטעמיה, דאמר רבי יוחנן: מניין שאין מזל לישראל - שנאמר +ירמיהו י+ כה אמר ה' אל דרך הגוים אל תלמדו ומאתות השמים אל תחתו כי יחתו הגויים מהמה, גויים יחתו, ולא ישראל. ואף רב סבר אין מזל לישראל, דאמר רב יהודה אמר רב: מניין שאין מזל לישראל - שנאמר +בראשית טו+ ויוצא אתו החוצה. אמר אברהם לפני הקדוש ברוך הוא: רבונו של עולם +בראשית טו+ בן ביתי יורש אתי. אמר לו: לאו, +בראשית טו+ כי אם אשר יצא ממעיך. אמר לפניו: רבונו של עולם, נסתכלתי באיצטגנינות שלי ואיני ראוי להוליד בן. אמר ליה: צא מאיצטגנינות שלך, שאין מזל לישראל. מאי דעתיך - דקאי צדק במערב, מהדרנא ומוקמינא ליה במזרח. והיינו דכתיב +ישעיהו מא+ מי העיר ממזרח צדק יקראהו לרגלו. ומדשמואל נמי, אין מזל לישראל. דשמואל ואבלט הוו יתבי, והוו קאזלי הנך אינשי לאגמא. אמר ליה אבלט לשמואל: האי גברא אזיל ולא אתי, טריק ליה חיויא ומיית. אמר ליה שמואל: אי בר ישראל הוא - אזיל ואתי. אדיתבי אזיל ואתי. קם אבלט, שדיה לטוניה אשכח ביה חיויא דפסיק ושדי בתרתי גובי. אמר ליה שמואל: מאי עבדת? - אמר ליה: כל יומא הוה מרמינן ריפתא בהדי הדדי ואכלינן. האידנא הוה איכא חד מינן דלא הוה ליה ריפתא, הוה קא מיכסף. אמינא להו: אנא קאימנא וארמינא. כי מטאי לגביה שואי נפשאי כמאן דשקילי מיניה, כי היכי דלא ליכסיף. אמר ליה: מצוה עבדת! נפק שמואל ודרש: +משלי י+ וצדקה תציל ממות ולא ממיתה משונה, אלא ממיתה עצמה. ומדר"ע נמי, אין מזל לישראל. דר"ע הויא ליה ברתא, אמרי ליה כלדאי: ההוא יומא דעיילה לבי גננא - טריק לה חיויא ומיתא. הוה דאיגא אמילתא טובא. ההוא יומא שקלתא למכבנתא, דצתא בגודא, איתרמי איתיב בעיניה דחיויא. לצפרא כי קא שקלה לה - הוה קא סריך ואתי חיויא בתרה. אמר לה אבוה: מאי עבדת? - אמרה ליה: בפניא אתא עניא, קרא אבבא, והוו טרידי כולי עלמא בסעודתא, וליכא דשמעיה. קאימנא, שקלתי לריסתנאי דיהבית לי, יהבתיה ניהליה. אמר לה: מצוה עבדת! נפק ר"ע ודרש: וצדקה תציל ממות ולא ממיתה משונה, אלא ממיתה עצמה. ומדרב נחמן בר יצחק נמי, אין מזל לישראל. דאימיה דרב נחמן בר יצחק אמרי לה כלדאי: בריך גנבא הוה. לא שבקתיה גלויי רישיה. אמרה ליה: כסי רישיך, כי היכי דתיהוי עלך אימתא דשמיא, ובעי רחמי. לא הוה ידע אמאי קאמרה ליה. יומא חד יתיב קא גריס תותי דיקלא, נפל גלימא מעילויה רישיה דלי עיניה חזא לדיקלא, אלמיה יצריה, סליק פסקיה לקיבורא בשיניה.  

6. Maimonides, Letter on Astrology.  Translation from I. Twersky, Maimonides Reader (New York: Behrman, 1972):

Know, my masters, that every one of those things concerning judicial astrology that (its adherents) maintain – namely, that something will happen one way and not another, and that the constellation under which one is born will draw him on so that he will be of such and such a kind and so that something will happen to him one way and not another – all those assertions are far from being scientific; they are stupidity. (p. 466)

I know that you may search and find sayings of some individual sages in the Talmud and Midrashim whose words appear to maintain that at the moment of man’s birth, the stars will cause such and such to happen to him.  Do not regard this as a difficulty, for it is not fitting for a man to abandon the prevailing law and raise once again the counter-arguments and replies (that preceded its enactment).  Similarly it is not proper to abandon matters of reason that have already been verified by proofs, shake loose of them, and depend on the words of a single sage from whom possibly the matter was hidden.  Or there may be an allusion in those words; or they may have been said with a view to the times and the business before him . . . A man should never cast his reason behind him, for the eyes are set in front, not in back. (p. 472)

7. רמב"ם הלכות עבודת כוכבים פרק יא

(ח) איזהו מעונן? אלו נותני עתים שאומרים באצטגנינות יום פלוני טוב יום פלוני רע יום פלוני ראוי לעשות בו מלאכה פלונית שנה פלונית או חדש פלוני רע לדבר פלוני. (ט) אסור לעונן אף על פי שלא עשה מעשה אלא הודיע אותן הכזבים שהכסילים מדמין שהן דברי אמת ודברי חכמים, וכל העושה מפני האצטגנינות וכיון מלאכתו או הליכתו באותו העת שקבעו הוברי שמים הרי זה לוקה שנאמר לא תעוננו, וכן האוחז את העינים ומדמה בפני הרואים שעושה מעשה תמהון והוא לא עשה הרי זה בכלל מעונן ולוקה. . . . (טז) ודברים האלו כולן דברי שקר וכזב הן והם שהטעו בהן עובדי כוכבים הקדמונים לגויי הארצות כדי שינהגו אחריהן, ואין ראוי לישראל שהם חכמים מחוכמים להמשך בהבלים אלו ולא להעלות על לב שיש תועלת בהן, שנאמר כי לא נחש ביעקב ולא קסם בישראל, ונאמר כי הגוים האלה אשר אתה יורש אותם אל מעוננים ואל קוסמים ישמעו ואתה לא כן וגו', כל המאמין בדברים האלו וכיוצא בהן ומחשב בלבו שהן אמת ודבר חכמה אבל התורה אסרתן אינן אלא מן הסכלים ומחסרי הדעת ובכלל הנשים והקטנים שאין דעתן שלימה, אבל בעלי החכמה ותמימי הדעת ידעו בראיות ברורות שכל אלו הדברים שאסרה תורה אינם דברי חכמה אלא תהו והבל שנמשכו בהן חסרי הדעת ונטשו כל דרכי האמת בגללן, ומפני זה אמרה תורה כשהזהירה על כל אלו ההבלים תמים תהיה עם ה' אלהיך.

8. רמב"ם הלכות תשובה ה:ד

אילו האל היה גוזר על האדם להיות צדיק או רשע או אילו היה שם דבר שמושך את האדם בעיקר תולדתו לדרך מן הדרכים או למדע מן המדעות או לדעה מן הדעות או למעשה מן המעשים כמו שבודים מלבם הטפשים הוברי שמים היאך היה מצוה לנו על ידי הנביאים עשה כך ואל תעשה כך הטיבו דרכיכם ואל תלכו אחרי רשעכם והוא מתחלת ברייתו כבר נגזר עליו או תולדתו תמשוך אותו לדבר שאי אפשר לזוז ממנו, ומה מקום היה לכל התורה כולה ובאי זה דין ואיזה משפט נפרע מן הרשע או משלם שכר לצדיק, השופט כל הארץ לא יעשה משפט . . .

9. פירוש המשנה לרמב"ם מסכת סנהדרין, הקדמה לפרק י

הכת הראשונה והם רוב אשר נפגשתי עמהם ואשר ראיתי חבוריהם ואשר שמעתי עליהם, מבינים אותם כפשטם ואינם מסבירים אותם כלל, ונעשו אצלם כל הנמנעות מחוייבי המציאות, ולא עשו כן אלא מחמת סכלותם בחכמות וריחוקם מן המדעים, ואין בהם מן השלמות עד כדי שיתעוררו על כך מעצמם, ולא מצאו מעורר שיעוררם, ולכן חושבים הם שאין כונת חכמים בכל מאמריהם המחוכמים אלא מה שהבינו הם מהם, ושהם כפשוטם, ואף על פי שיש בפשטי מקצת דבריהם מן הזרות עד כדי שאם תספרנו כפשטו להמון העם כל שכן ליחידיהם היו נדהמים בכך ואומרים היאך אפשר שיהא בעולם אדם שמדמה דברים אלו וחושב שהם דברים נכונים, וכל שכן שימצאו חן בעיניו. והכת הזו המסכנה רחמנות על סכלותם לפי שהם רוממו את החכמים לפי מחשבתם ואינם אלא משפילים אותם בתכלית השפלות ואינם מרגישים בכך, וחי ה' כי הכת הזו מאבדים הדר התורה ומחשיכים זהרה, ועושים תורת השם בהפך המכוון בה, לפי שה' אמר על חכמת תורתו אֲשֶׁר יִשְׁמְעוּן אֵת כָּל הַחֻקִּים הָאֵלֶּה וְאָמְרוּ רַק עַם חָכָם וְנָבוֹן הַגּוֹי הַגָּדוֹל הַזֶּה, והכת הזו דורשין מפשטי דברי חכמים דברים אשר אם ישמעום העמים יאמרו "רק עם סכל ונבל הגוי הקטן הזה."

The members of this group are poor in knowledge.  One can only regret their folly.  Their very effort to honor and exalt the sages in accordance with their own meager understanding actually humiliates them.  As God lives, this group destroys the glory of the Torah and extinguishes its light, for they make the Torah of God say the opposite of what it intended.  For He said in His perfect Torah, “The nations who hear of these statutes shall say: Surely this great nation is a wise and understanding people” (Deut 4:6).  But this group expounds the laws and the teachings of our sages in such a way that when the other peoples hear them they say: “Surely this little people is foolish and ignoble.”  (translation from I. Twersky, Maimonides Reader, p. 407)

10. שולחן ערוך יורה דעה הלכות מעונן ומכשף סימן קעט

סעיף א אין שואלים בחוזים בכוכבים ולא בגורלות. הגה: משום שנאמר: תמים תהיה עם ה' אלהיך (ב"י בשם תוספות דע"פ ובשם ספרי). וכ"ש דאסור לשאול בקוסמים ומנחשים ומכשפים (פסקי מהרא"י סי' צ"ו).

סעיף ב נהגו שאין מתחילין בב' ובד',ואין נושאים נשים אלא במילוי הלבנה. הגה: ולכן נהגו ג"כ להתחיל ללמוד בר"ח, כי אף על פי 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 /רפ"ג/) כמו שנתבאר.