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By Rabbi Dovid Markel
The Jewish Catalonian thinker, Avraham bar Hiyya the Nassi (ca. 1070 – ca. 1136), began his career in the city of Barcelona and seems to have finished it in the area around Provence. He was clearly a brilliant mind; known as a mathematician, philosopher, astronomer and an astrologist.  While his works have survived, his history, for the most part, has not. Indeed, most of what we are able to glean about his life are from bits and pieces of anecdotal statements throughout his work.
From a secular perspective, he was revolutionary in the sense that he was the first to explain the quadratic solution in Europe, and being the first author to write scientific thought in Hebrew, he was a revolutionary there as well. Being that he was the first to truly author astronomical works in Hebrew, another interesting facet of his work is his development of terminology and lexicon to describe concepts in astronomy.
Because he is often referred to as “Savasorda” or “HaNassi,” it is often assumed that he held some governmental position of authority. Indeed, it has been suggested that he may have been a royal astrologer.
While he was revolutionary in many areas, he has, for the most part, been forgotten by history and largely ignored, as he was overshadowed by the works of individuals that came after him. Possibly, the very reason for this is due to the fact that he was a revolutionary; the strides that he made were quickly out-paced by individuals such as Avraham Ibn Ezra—who although used his tables, was considerably more influential than Bar Hiyya. Because Avraham Ibn Ezra came on the scene of Jewish science immediately following Bar Hiyya and was vastly more popular, Bar Hiyya’s contribution were all but forgotten.
This luck—or lack thereof—appears to be especially pronounced concerning Avraham bar Hiyya’s letter regarding the halachik justification of studying astrology and being cautious in following its warnings. For although much of his thought has been studied and researched as late, his astrological works and his letter have been largely overlooked. This paper will deal with aspects of Bar-Hiyya’s halachik defense for practicing astrology.
On the verse (Devraim, 30: 12) that says pertaining to the whereabouts of Torah, “It is not in heaven,” the Medrash states—in the sage Shmuel’s name—that it means that “the Torah is not found amongst astrologers whose craft is in the heavens.”  When Shmuel is challenged that he is both an astrologer and great in Torah, he responds, “I would only gaze at astrology during moments when I was free from Torah—when I would enter the water chamber.”
Indeed, Rabbi Avraham bar Hiyya, though a tremendous sage in various schools of science and knowledge, was less known as a Talmudic sage. While clear from his letter that he had a familiarity with Talmudic literature—at least those sections that deal with astrology—from the various works that he authored it is obvious that Talmudic study was not his primary focus. It is therefore important—in my opinion—to put the letter in perspective. Though it is written in Halachik jargon, one must realize that it was written by an individual who was known for his science rather than his Halacha.
This is expressed in this that in the eight works attributed to him, they all in some way deal with astronomy or astrology except for his Hegyon Ha-Nefesh Ha’asuba (The Meditations of the Sad Soul), which is a philosophical study of human nature.
This essay will focus on the letter that Rabbi Avraham bar Hiyya wrote to the much more famous Halachik sage, Rabbi Judah Barzillai of Barcelona, concerning the prohibition of “consulting Chaldeans.”
While the letter under discussion revolves around the wedding of a certain student of his—which could lead a reader to believe that Bar Hiyya was a teacher of Judaic studies—there is no reason to assume that he was a student of Talmud or the like—but rather, in all probability he was a teacher of the sciences of the stars or in mathematics; these latter topics were areas that he clearly was an expert in.
Interestingly, Bar Hiyya himself writes two statements that display that—at least in the eyes of his townsmen—he was not regarded for his expertise in Jewish law. For, when his detractor forced the wedding of his student to occur in an inauspicious astrological hour, Bar Hiyya’s protest fell on deaf ears and was ignored. Those that were present considered his actions to be in opposition to Jewish law; Bar Hiyya even goes so far as to write that they actually viewed him as a sinner. Surely, were he to have been a reputable Halachik authority, his words would have been more respected rather than being disparaged; would he to have been a rabbinic authority, he’d be honored for his words rather than vilified. 
Bar Hiyya writes, that because he was viewed as a sinner, he desired to defend himself to save face before man and G-d:
Because the manner came through me, it was in my eyes, as if all those that heard about it considered me a transgressor and a sinner. Therefore, I must give a reason for my words to save myself from G-d and my nation, as the verse (Bamidbar 32:22) states: “you shall be absolved from the Lord and from Israel.”
Surely this indicates his standing in matters of Jewish Law in the opinion of his townsfolk.
Additionally, towards the end of the letter, he again expresses how he is held in antipathy rather than admiration, saying that “When I was a child and a youth, I was respected by virtue of the high esteem in which I was held by grandness and kings, but now, when I am an old man, high regard has been transformed into enmity.”
Clearly, from the fact that not only were his words not taken into account, but that he was looked upon as “a sinner” and where there was “high regard” there was now enmity, it is clear, that though he was respected as a scientist of worldly knowledge, he was not considered a Halachik authority and his opinions were thus ignored and he was denigrated.
On the other hand, he was an expert in Judaic astronomy and the manner in which to create a Judaic calendar. Indeed, various Halachik rulings concerning how to create a Jewish calendar can be traced back to him.
No matter that his expertise was not Halacha, the letter is nevertheless of tremendous import.
The letter is beautifully and systematically written and is one of the first attempts to defend Judaic astrology in a systematic way. Because of the clear classifications and differentiations expressed therein, it seems to have similarly influenced the thought process of subsequent generations—so that later Halachik commentators seem to have adopted the views originally presented within the letter. The letter is methodically written and deals with various aspects of the Judaic concern of consulting astrological signs to determine how to arrange one’s life. It is no wonder then, that it had an effect on subsequent writers.
Due to the many aspects discussed in the letter, we will not focus on all its facets, but will instead focus on a few essential points. Rather than attempt—in this short work—to deal with the strength or veracity of all his many points, we would rather attempt to distill the crux of the essential argument he wishes to make.
Of our goals is to determine the essential argument that he makes for practicing astrology. We will attempt to come to a conclusion whether or not the argument is scientific or Talmudic—meaning to say, whether or not the argument is essentially a scientific one couched in Halachik jargon or purely Talmudic.
We will discuss Bar Hiyya’s stance on astrology vis-à-vis his interlocutor, and employ Maimonides’s statements concerning astrology as a dialectic to compare and contemplate Bar Hiyya’s stance concerning acceptable Judaic astrology. Using Maimonides as the archetypical anti-astrologist helps us zone in on the axiomatic philosophical approach of the two men and appreciate their difference; a difference that is sure to have ramifications well beyond the question of astrology.
1.2 Relationship with practical astrology
The first matter that we will turn our attention to is Bar Hiyya’s stance concerning practical astrology. While the letter suggests that he was a practitioner of the art, other sources suggest that in truth he had a more ambivalent stance.
Baron suggests that though astrology was certainly an important part of Bar Hiyya’s intellectual corpus, he seemed to have approached the subject with a certain level of restraint. Therefore, in his work there seems to be an intentional separation of the field of astronomy and philosophy from his astrological writing.
It can perhaps be postulated that the nature of Bar Hiyya’s weariness was due to the fact he was a revolutionary in his field, embarking on vistas of scientific thought that had hardly been touched within the Jewish world. The atmosphere in which he lived was one that was new to the secular sciences and weary of their import. Being the first to write on these topics specifically for the Jews—as demonstrated in his writing in Hebrew—not being on terra firma surely brought with it much tension and doubt concerning the value, importance and permissibility of his works.
While it seems clear that Bar Hiyya had adequately convinced himself—and others—about the importance of his astronomical studies, it can be assumed that he himself—as well as others—were not as convinced about the Judaic importance of astrology.
To support this assertion, one need look no further than examine the preface to his astronomical work Tzurat Ha-Aretz, where he essentially expresses this point himself. There he demonstrates an inner tension concerning his writing works on the secular sciences. After he explains how gazing at the stars causes one to appreciate the greatness of G-d and instills the fear of Him into the individual’s heart, he states:
Because, one that gazes on the creation of heaven and earth and the content of their form, and will contemplate the movement of the stars and the wisdom of their structure, will understand the wisdom of his Master and Creator. About such a person our rabbis have stated (Talmud Shabbos 75a), “He who knows how to calculate the cycles and planetary courses, but does not, of him Scripture says (Yeshayahu 5:12), ‘but they regard not the work of the Lord, neither have they considered the operation of His hands.’” What is derived, is that one who does calculate them, gazes upon “the work of the Lord” and sees “the operation of His hands.” One’s hand will be strengthened from every angle: For, someone who prefaces Torah study to the best of his ability and toils in her and keeps her commandments and together with these actions examines the wisdom of the stars, learning it and toiling in it—is not involved in a worthless activity—rather he is proficient in a wisdom which causes him to believe the hidden (depth) of faith and straightens before him the path of true fear. Indeed, in many places it is necessary for the commandments.
Bar Hiyya is clearly intent on convincing his reader that a study of the sciences “is not a worthless activity,” but is instead necessary for an individual who truly wishes to connect to his Creator and observe His commandments.
From the wordiness and length that he goes to prove that astronomy was an important science for the Jew to be involved in, it is clear that as a trailblazer he must have faced an inner and outer tension about the value of his work.
Although he demonstrated the importance of astronomy in the preface of this work, astrology was a much more delicate issue—even for him—and it seems that he too was not entirely convinced of its value.
That he was somewhat apprehensive to utilize astrology to determine world events can be seen in the lengthy disclaimer that he makes in his work Migilat HaMegaleh in the chapter that deals with astrological history and the coming of Moshiach.
There he writes:
The content of this gate are definitely remains and dregs compared to the matters that have passed in the previous gates. For, those words were based upon scholars and prophets and derived from holy writing—the words of the living G-d. However, the words of this gate are built upon the opinion of fools and carved from the houses of the frivolity of the nations. Were we to be proper, we would clutch from all angles the ways of the men of pure faith, it would not at all be a necessity—in this scroll—for this gate. For the proofs that we have explained in the previous gates would be sufficient… However, because this work can reach the hands of those involved in secular wisdom—who are small in faith—and do not delve into the secrets of thought. They will perhaps think that the opinion of the nations is different than ours…I contemplated this and permitted myself to involve myself in this matter… as I saw from the words of our rabbis of blessed memory that they do not invalidate this wisdom and say that it is false. However, on the contrary, from their words, it seems that they admit to it.
He clearly states that this wisdom of astrology is “remains, and dregs compared to the matters” that he spoke about before, which were words of Torah. He himself writes, that in truth, all the matters of the chapter need not be written were he to have lived in a perfect world.
While it is impossible to truly know what he himself believed concerning this wisdom, the fact that he put in this disclaimer is telling. The reason is either because as he writes, “that people will perhaps think that the opinion of the nations is different than ours”—and the astrology that he does write, is really a defense for Torah and not an end on its own. This articulates, though his own ambivalence, that he himself would not write a section on astrology.
Or, if one wishes to read into his writing, one can perhaps postulate that the reverse is the case. While he places a disclaimer before his discussion of astrology, it is perhaps because he was fearful of the reaction of his coreligionists who would read the work. Perhaps he was anxious about the disdain that he perceived that they would have concerning this chapter, and therefore wrote a disclaimer as a defense for his writing it. Whatever the case may be, it is clear that he had an uneasy relationship with astrology and was apprehensive to write about it. 
The reason for the difference is simple. While abundantly clear that Judaism had no problem with astronomy—as it is impossible to assume that it is somehow antithetical to faith in G-d—there was a certain valid complaint against astrology.
Indeed, this is the topic of the letter that this paper will deal with—that from a superficial examination of the Talmud, it is possible to assume that the Talmud forbids consulting with astrology. While he believed that he was vindicated in his polemical defense of astrology, it is possible that the internal and external pressure caused him to take a somewhat ambivalent approach towards its study and application.
Interestingly, remnants of this internal struggle can perhaps be seen in Bar Hiyya’s own work. In the preface to his astronomical work, Tzurat Ha-aretz, he states that if G-d will help him, he will author an astrological guide. Though he seems to have planned on writing it, the project either never came to fruition—for some reason or other—or it was written but no longer extant.
The second section of the wisdom of the stars… is the benefit that people enjoy from it in this world. Its scholars however, that understand the axioms of this wisdom do not prescribe it this advantage—for, its proofs are not complete, but rather derive from reason and trial. Nevertheless, if the Almighty will come to my assistance to complete the work on observational science from beginning to end, I will, with the help of G-d place unto my heart to explain the “art of trial.”
Although possible that this work was written and somehow no longer extant, this seems unlikely. For given the popularity of astrology—and of Bar Hiyya himself—in the medieval world, one would assume that an astrological work that he authored would instantaneously become popular and many copies would be made. Indeed, a popular astrological work would be assumed to survive, instead of more obscure projects. Rather, it is more likely that for some reason or another this work was never written.
While possible that the reason is because the funds from his patron dried up or some other technical reason—it is also definitely plausible that there is another reason—based on the challenge against the permissibility of astrological practice.
We would like to postulate that the reason that he did not write this work is due to one or a mix of three reasons: 1) His own inner turmoil about the value of such a book. 2) The backlash that he feared he would receive from authoring an astrological work. 3) Perhaps he—or his patron—conceded that there were Judaic issues with practical astrology.
It is possible, as seen in the preface to the work Tzurat Ha-aretz, that in addition to convincing others about the importance of astronomy, he was as well convincing himself of its prominence in Judaism. While he demonstrated that there is a clear value in the study of astronomy, as its proficiency teaches the person the awesomeness of his Creator and has practical application, as it necessary in the fulfillment in various commandments, there is much less justification for the study of astrology.
More importantly though, astrology was clearly a contested subject in the time and place that he lived. This is clearly demonstrated in the debate concerning astrology, which was the impetus for the letter defending practical astrology that this paper deals with. It seems clear from the letter, that those leaning against practical astrology were vocal and persuasive.
This is demonstrated in the fact that those that claimed that he was sinning in appointing a wedding using astrological considerations overpowered those there that were sympathetic—even the groom, who clearly believed in astrology, was forced to be wed in a time that was not suitable according to astrology, “against his will.” Not only did they force the groom to marry—against his will—in an inauspicious time, but more so, Bar Hiyya states that all that were there viewed him as “a sinner.”
It is entirely possible therefore, that in such a hostile environment, where using practical astrology carried with it the stigma of being labeled a sinner, Bar Hiyya would be hesitant to author such a work.
Though less plausible, there is as well a third possibility that caused Bar Hiyya to refrain from authoring this work. It is possible that after this episode Bar Hiyya retracted his view concerning practical astrology. It is conceivable that Judah b. Barzillai responded orally or in writing to Bar Hiyya, causing him to recant his views. For, while Bar Hiyya’s letter to Rabbi Judah b. Barzillai is extant, a response is not.
Indeed, at the end of Bar Hiyya’s letter, he begs Rabbi Judah b. Barzillai to respond to his letter, saying:
He should not leave us standing in confusion and going in darkness. For, showing the truth and showing the proper path, is the character of the wise and the custom of the intelligent and upright. Indeed, we and all who hear his words must thank him and praise him on his tremendous kindness and goodness, his easy-spiritedness and his humility. If he sees in my words that they are a mistake and nonsense, empty words and craziness and are not proper to say them or to express such claims; he should be abundantly kind with me, bestow his righteousness and open his hands, to show me which of my paths are broken and for what reason I cannot rely upon them. The day that I hear his claims I will admit to by debt and will say “I concede, I concede.”
Clearly, out of tremendous respect for Rabbi Judah b. Barzillai’s opinion, Bar Hiyya was willing to admit to having made a mistake, if indeed that mistake was pointed out. While there is no extant response from Rabbi Judah b, Barzillai, it is indeed possible that he responded—explaining to Bar Hiyya the mistake of his ways.
Although Sela has pointed out that Rabbi Judah b. Barzillai himself authored an astrological horoscope in his work on Sefer Yetzira, which makes it hard to believe that Barzillai was anti practical astrology—it is entirely possible that to Barzillai there was a focal difference in authoring a horoscope—which is merely predictive—and authoring an astrological guide or appointing a wedding based on astrological considerations—which is instructive—thus possibly falling more into the parameters of “asking Chaldeans.”
That being the case, one can hypothesize that the reason why Bar Hiyya did not author an astrological guide is because he perhaps conceded that there was indeed a Judaic issue in doing so.
Expressed in Bar Hiyya’s letter is that it was written towards the end of his life. Although Tzurat Ha-aretz, where he promises to write an astrological work, was his first work, it is possible that he put it off for one of the reason expressed herein and never wrote it because he eventually conceded that writing an astrological guide was problematic according to Judaism, as doing so was perhaps an issue of “asking Chaldeans.” 
So, while he was definitely an astrological sympathizer, the time that he lived in was perhaps not ready for an astrological guide for one of the many reasons expressed above.
2.1 The authorship of the letter
Throughout the literature on Bar Hiyya it is often offhandedly mentioned that not only was Rabbi Judah b. Barzillai the recipient of Bar Hiyya’s polemic, but indeed he was the very individual that caused the debate from the onset. It was because Rabbi Judah b. Barzillai forced the wedding to precede, publically shaming Bar Hiyya, that he felt it necessary to respond with a letter in which he defends practical astrology.
However, Sela, in his work on Bar Hiyya’s astrological thought has questioned this assertion, expressing that although Rabbi Judah b. Barzillai was the recipient of the letter, he was possibly not its instigator. Indeed, according to Sela, it is entirely possible that Bar Hiyya wrote the letter to him, as he thought that it was possible that Rabbi Judah b. Barzillai would come to his defense.
Sela himself does not come to any conclusive inference, but rather leaves the matter with some doubt. He writes:
Earlier research considered Rabbi Judah b, Barzillai of Barcelona, the addressee of Bar Hiyya’s letter, to be his very detractor in the wedding or, at least, an opponent of astrology. Nevertheless, only ambiguous and limited information about Judah b. Barzillai’s role may be obtained from the two extant manuscripts of the epistle…An examination of the material employed in in the Commentary on Sefer Yesira not only shows that Judah b. Barzillai engaged in mathematics and compiled in Arabic a treatise on the nine Indian numerals, but also reveals that he was familiar with the other “external sciences”…most notably, with astrology. When coming to illustrate the motion of the orb and its decrees (gezerot), Judah b. Barzillai drew up a complete horoscope…It is not completely clear whether Bar Hiyya’s addressed his apologetic epistle to Judah b. Barzillai because the latter was his detractor, or because Bar Hiyya regarded Judah b. Barzillai as a continent and receptive addressee before whom he could voice his defense to astrology.
The crux of Sela’s argument is—as expressed above—in Rabbi Judah b. Barzillai’s own work, Commentary on Sefer Yetzira, that Rabbi Judah b. Barzillai himself authors an astrological horoscope. That being the case, it seems exceedingly strange that Rabbi Judah b. Barzillai would be that individual who forbade the wedding from occurring at an inauspicious astrological time.
Instead, Sela suggests that Bar Hiyya wrote the letter because he saw in Rabbi Judah b. Barzillai an individual that was sympathetic to astrology who would perhaps come to his defense.
We would like for a moment to reflect a little more on this issue to see if it is perhaps plausible that indeed Juda b. Barzillai was the instigator of the letter.
Interestingly, when Bar Hiyya, at the end of the letter, addresses Rabbi Judah b. Barzillai, he refers to him as one whom “all wisdom that is known to all men on earth are illuminated to him like the streets of Nehardea.” This expression is borrowed from the Talmud’s (Berachot 58b) expression that Shmuel stated: “I am as familiar with the paths of heaven as with the streets of Nehardea.” It seems clear, that by using this expression Bar Hiyya was alluding to the fact that Rabbi Judah b. Barzillai himself was an expert in the wisdom of the stars. Whether or not his point was that because Judah b. Barzillai was an expert in these sciences, he therefore wished that he come to his defense, or if he was expressing his shock that Judah b. Barzillai would condemn something that he himself was an expert in, is one of the very questions that we seek to analyze.
Our intent here is to reconsider the evidence mentioned, discuss its merits, bring more support for this theory and continue to question this point—postulating that this it is perhaps not the case, and that indeed Rabbi Judah b. Barzillai was the instigator of Bar Hiyya’s letter pertaining to astrology.
We will begin with support for Sela’s theory, that the instigator was not Rabbi Judah b. Barzillai:
Examining Bar Hiyya’s letter, it is apparent that when articulating the story that was the impetus for the letter, he goes into very particular detail. We would like to postulate that such detail only seems in place when describing the event to someone who does not yet know the story.
For, had the recipient known the story, there would be no reason to tell them. Because, however, such minute detail is indeed written, one can perhaps extrapolate from this that Rabbi Judah b. Barzillai was not the individual that inspired Bar Hiyya to write the letter.
Additionally we would like to postulate, that there are other irregularities in the description, if indeed Rabbi Judah b. Barzillai was the individual that forced the wedding to occur in an inauspicious astrological time.
The first place that is important to examine in order to determine the identity of the individual that prompted the writing of the letter, is the description of the individual by Bar Hiyya himself.
In describing the event that caused the letter to be written, Bar Hiyya writes:
Something occurred to me regarding this matter that I need to explain regarding all the allegations, confusions and questions until the truth of this matter is elucidated. There was a certain student who was greatly beloved by me and precious in my eyes, who was going to the chupa (marriage canopy) on Friday. I agreed that he should be brought to the chupa in the third hour of the day—when the congregation leaves the synagogue…it was proper according to the movement of the stars. However, the matter was postponed due to a chance burial in the city. The attendees of the wedding who were the heads of the congregation and its leaders decided to preface the burial of the dead. The congregation returned at the end of the fifth hour and the beginning of the sixth which is a time of coupling (?) zug and is ruled by Mars. It was not proper in my eyes due to the movement of the stars and the mazal tzomea’ach (rising zodiac?). When I saw this, I told him: “Since it has already been postponed until the sixth hour, wait until this hour passes and the seventh hour comes, which is separate and is ruled by the sun and is proper to begin any matter within it…” The man listened to my advice and was convinced by my words and he and his acquaintances decided to wait. However, there was individual there who found this matter problematic and said, “This waiting is equivalent to ‘asking Chaldeans,’ and our Rabbis stated, ‘one may not ask Chaldeans.’ Someone who does this act transgresses the words of the Rabbis…” He repeated these words a second and third time until the groom went to the chupa at the sixth hour against his will.
Superficially, when examining the details of this description, there is indication that the individual who so intensely disagreed with Bar Hiyya was not Rabbi Judah b. Barzillai. This is so because of various points.
Firstly, as mentioned, Bar Hiyya is extremely detailed in the story in a manner that seems irregular, would the recipient to have had prior knowledge of the incident. It is understood therefore, that being that Bar Hiyya does explain all the particular details of the story, that the instigator and the recipient of the letter are not one and the same person.
Additionally, the particular language of “However, there was individual there who found this matter problematic who said, ‘This waiting is equivalent to “asking Chaldeans,”’” is also somewhat odd if the individual was Rabbi Judah b. Barzillai himself and the letter was addressed to him as well. Were Judah b. Barzillai to have been that “individual,” it seems likely that he would have either referred to him with an honorific, or would have therein expressed that the recipient was that individual who forbade the wedding—saying “you” instead of expressing that it was an anonymous individual.
On the other hand, perhaps the end of the letter does express that the recipient was as well the instigator.
There he writes:
Indeed, although he writes to him as a student would a master, his choice of words intimates that Rabbi Judah b. Barzillai was the one that forbade the wedding.
For, when he mentions again the individual who forbade the wedding, he almost clearly indicates that it is the recipient of the letter—Rabbi Judah b. Barzillai, saying: “Although it is known and clear that all his actions are for the sake of heaven and fear of G-d. Indeed, all the things we prefaced, from his mouth we learned, from his water we drank.” The connotation of coupling the one who forbade the wedding with a statement of respect concerning the individual, intimates that it was indeed R. Judah b. Barzillai—whom he respected as his teacher—who forbade the wedding.
Additionally he writes, that those that denigrated the art are “wise, righteous, pious, clever and renowned individuals.” This expression as well, one of high praise of the individual(s) who forced the wedding, is perhaps additional support that the detractor and the recipient of the letter are one and the same person.
He writes concerning this debacle:
From my youth on, I have been busy learning, dealing with, inquiring and teaching the science of the stars (Chochmat Ha-Kochavim). At first I saw myself getting wisdom and discretion, without committing any sin or being to blame, but now, when I see that wise, righteous, pious, clever and renowned people disagree with me, I despise my art…
From these two above quotes it does seem safe to assume that the recipient of the letter—Rabbi Judah b. Barzillai—was as well its instigator.
While, as expressed above, it seems rather strange that Rabbi Judah b. Barzillai would be against Bar Hiyya’s actions, when he himself seems to have believed in astrology and authored, among other things, an astrological horoscope, it is possible that it was precisely this issue that bothered Bar Hiyya.
This is perhaps what he hints to in his statement, “From his mouth we learned, from his water we drank and all wisdom that is known to all men on earth are illuminated to him like the streets of Naharda’a.” Bar Hiyya intimates that he learned, at least aspects of this wisdom, from Barzillai himself. Being that Rabbi Judah b. Barzillai himself taught this very wisdom to Bar Hiyya, why all of a sudden does he seem to have changed his mind and express that using astrology is prohibited?
The resolution of this apparent paradox is perhaps the general tension that many medieval Jews grappled with.
On one hand, they generally viewed astrology as a science rather than a superstition, and on the other, they were aware of such statements in the Talmud such as (Shabbos 156a), “Israel is immune from planetary influence,” and (Pesachim 113b) statement concerning the prohibition of consulting Chaldeans. Because of this, many rabbis were somewhat ambivalent towards practical astrology and had a somewhat nuanced approach.
Although they accepted many of its statements as truth—and even as science—they were weary to act practically on this knowledge. It was perhaps for this reason that Rabbi Judah b. Barzillai prohibited the delaying of the wedding, although in theory he believed in astrology.
To better appreciate this theory though, it is pertinent to preface an overview of the prohibition of asking Chaldeans.
3.1 The Prohibition of asking Chaldeans
The question of whether or not astrology is an accepted science for a Jewish person is one that has bothered the Medieval Jewish mind very much. Contrary to the perhaps popular belief—probably due to Maimonides’s strong effect on our thinking—that those who believed in astrology were superstitious, the case of Bar Hiyya and others demonstrates that it was specifically those individuals who had a predisposition to the sciences that were more easily disposed to believe in astrology.
However, the Jewish thinker was faced with an inner turmoil—in many ways no different than the turmoil that many modern Jewish scientists might be faced with. How does one reconcile what one knows from the sciences and the suggestions that it makes, with the Torah directives? Is one to ignore science because of a Talmudic prohibition?
This was the problem that bothered Bar Hiyya and others—as the debate of the permissibility of astrology was one that flared up time and again in the Middle Ages. It was this question that arose for Bar Hiyya as well.
Generally, one of the issues facing the Jewish mind concerning astrology was that, while on the one hand there the Talmud states that there is a prohibition of “asking Chaldeans,” on the other hand Talmud seems to endorse many elements of astrology.
How to reconcile these issues is the primary function of Bar Hiyya’s letter.
While the Torah does not—in any prohibition—mention Chaldeans, the Talmud derives the prohibition from a verse that deals with similar actions:
Be wholehearted with the Lord, your G-d. For these nations, which you are to possess, hearken to Me’oninim times and Kosmim, but as for you, the Lord, your G-d, has not given you [things] like these.
The Talmud (Pesachim 113b) states:
Rabbah b. Bar Hanah said in the name of R. Shmuel b. Martha in Rab’s name on the authority of it. Jose of Huzal: How do we know that you must not consult Chaldeans? Because it is said (Devarim 18:13): Thou shalt be whole-hearted with the Lord, your G-d.
When he was attacked that his actions were prohibited, as they were akin to asking Chaldeans, his response was to differentiate between “asking Chaldeans” and general astrology. One is more obsessive while the other deals with more generalities.
The manner in which he resolved the issue was to compartmentalize astrology into sections; the parts that were wisdom were permitted and the parts that were obsessive of magic were forbidden. While generalities were permitted, it was—according to Bar Hiyya—the obsessive particularities that were forbidden.
He expresses this saying:
From all that we have prefaced, it is clear that the wisdom of the stars is proper to learn and to adhere to. However, because it can arise in an individual’s heart that the Rabbis’ prohibition “to ask Chaldeans” is the wisdom of the stars that we spoke of until now, we will now investigate the difference between them. We will say that the wisdom of the stars only makes known the generalities what will come to be and cannot know the particulars…this is clear and agreed upon by all scholars of this science.
It is in the second grouping that Bar Hiyya places the Chaldeans, saying that being involved with these particulars and obsessing over them is contrary to having trust in G-d. However, being involved with generalities is no different than an individual who goes to a doctor for advice.
It is possible that his detractor—Rabbi Judah b. Barzillai—believed in astrology as well, but rather than placing the line where Bar Hiyya placed it, he drew it elsewhere. Thus, even according to Judah b. Barzillai, there are certain permissible aspects of astrology—as seen in his writings.
4.1 Between Maimonides and Bar Hiyya
Though Bar Hiyya believed that astrology was a science, it is clear that Maimonides did not. It is because of this difference that Maimonides’s response to astrology was very different to Bar Hiyya’s. Indeed, it can perhaps be suggested, that though Maimonides’s letter concerning astrology was written is response to the astrology of Ibn Ezra, the letter more clearly negates the opinions postulated by Bar Hiyya. So, perhaps although Bar Hiyya is not mentioned in the letter, Maimonides’s essential point is to negate the very premise postulated by Bar Hiyya.
We will attempt to show that this is an axiomatic difference between Maimonides and Bar Hiyya. For Maimonides, the prohibitions of the Torah are to accomplish the end of removing the person from foolish beliefs and superstition. If the Torah prohibits certain actions, it must be because those acts are inherently foolish.
For Maimonides, it would be an oxymoron to say that the Torah would prohibit a practice that is valuable, scientific and meaningful, as for Maimonides, the purpose of Torah law is that it should be a guide for truth.
Not so with Bar Hiyya. In his worldview an act can be true and valuable yet still prohibited by the Torah.
This is clear in his understanding of the prohibition of “asking Chaldeans.” For although he prohibits one to ask Chaldeans, he states that one should follow their advice, as it contains wisdom. For him, the commandments are not to separate the individual from falsehood, but that a person should attach himself to a deeper truth and reliance on G-d.
4.2 Science & Superstition
When Jews questioned the permissibility and veracity of astrology for a Jewish person, there were generally four responses: 1) that it is patently false and therefore forbidden, 2) it is perhaps true and nevertheless prohibited, 3) it is untrue but has psychological benefit and forbidden, and 4) that it is true and permitted.
The preamble to the letter opens with an explanation to the verse (Tehillim 34:15), “Shun evil and do good, seek peace and pursue it,” which seems to be from a Medrashic work that is no longer extant. In this quote, it expresses that “if you lust after something that wisdom and knowledge do not praise, shun the evil lust and accept the good advice of wisdom.”
It is upon the premise that in all matters man should follow wisdom rather than folly, that Rabbi Avraham bar Hiyya builds his thesis about the permissibility of astrology.
To him, the main question about the use of astrology is if it can be considered a genuine science or a spurious and counterfeit one. In his mind, if something is true and reasonable, not only may a person follow such a science, but Torah actually mandates this course of action. However, the parts that were obsessive and irrational were indeed forbidden by Bar Hiyya as well, and parts of it are considered to be magic.
It was this very point that Maimonides wished to negate. He too seems to have been convinced that one must follow reason—and that if something is indeed scientifically true it cannot be forbidden. The question, however, was if the matter was true; for in his mind it was foolishness and falsehood.
The primary point that Avraham bar Hiyya wishes to express is the notion held by most medieval thinkers—that astrology was a logical science as opposed to superstition. It is due to this important facet of astrology that he believes that it is a “kosher science” for Jew and gentile alike.
It is interesting to note, that in the preface to his astronomical work entitled Tzurat Ha-Aretz, Avraham bar Hiyya takes a somewhat different route. So, although in the letter at hand he stresses multiple times that it is prudent for every individual to hearken to the advice of the “wisdom of the stars,” there he goes so far as to say that one cannot refer to it as a science, but that it is rather referred to as “trade.”
The second section of celestial knowledge…speaks of the happenings that occur on earth, that the movement of the stars testify affirm and cause…from the proofs that are given to the wise of this body, from the happenings in their times and the trials ((נסיונות that their forbearers have given to them. This section is not considered wisdom or knowledge. It is instead proper to call it the art of trial (מלאכת הנסיון)… Rather, because the majority of people and the populace see that this practical application is a derivate of the observational wisdom and the gain derived from it for individuals in this world. However, the scholars that understand the axioms of this wisdom do not prescribe this advantage to it, for its proofs are not complete, but they rather derive from reason and trial.
Clearly, in his polemical work to defend his astrological practices, he desires to be more assertive in his claims pertaining to the value of the science. He therefore refers to it as a wisdom, although he himself admits that “its proofs are not complete” and they are rather derived from “logic and trial,” as opposed to what he states there regarding astronomy that it is an observable science with complete proofs.
There is, however, not a true contradiction, as there he does indeed say that astrology is “a derivative of observational wisdom” and that it is indeed derived from “reason and trial,” although admittedly the proofs are incomplete. His main correlation—that he mentions twice—is the comparison of astrology to medicine, which although as well—at the time—was in no way an exact science, is still one that it is prudent to follow the advice of.
In explaining what type of wisdom one should follow, Bar Hiyya writes:
The elucidation of this matter: If you plan to travel and a wise man who loves you tells you not to commence the journey at this hour, whether because it is it is dangerous or a time of zug (coupling?) or the time of Saturn or Mars; or if he tells you do not commence your journey on this day, as it’s mazal (zodiac?) is not good for travel—you should be attentive to his words and not leave. Likewise, if there is a food that you desire to eat before you, and the doctor tells you not to eat it because it is detrimental to the digestive system, listen to his words, and don’t eat it. This is the meaning of “Shun evil and do good,” Shun the bad decision and follow good advice.
Bar Hiyya desired to elevate the importance of astrology to the extent, that in his opinion—not only may one follow the astrological advice—but he believed that Torah ethos advise one to follow the advice of an astrological scholar as well. The reason that he believes that Torah itself would dictate to follow astrological advice is that one should follow the guidance of wisdom—and astrology is wisdom.
Conversely, while Bar Hiyya believed that there was wisdom in astrology, Maimonides believed it to be superstition and therefore forbidden. It possibly can be said, that though at the surface the two seem to be arguing about whether it is permissible or forbidden, in truth, the permissibility is secondary to their primary claim.
Maimonides believes that astrology is a spurious and counterfeit science. In his grandiloquent claim that he has read all astrological works and found them to be foolish, he asserts that no true philosopher believes in astrology and that it is only the belief of the weak-minded.
In his mission to uproot from Judaism all forms of fantasy, superstition and falsehood, he states that it is forbidden to engage in astrology. Interestingly, while he himself—as expressed in the letter—is aware that the Talmudic sages engaged in astrology, he nevertheless declares it to be forbidden, as derived from a biblical prohibition.
This can be seen in Maimonides’s Mishna Torah, where he writes: 
It is forbidden to tell fortunes. [This applies] even though one does not perform a deed, but merely relates the falsehoods which the fools consider to be words of truth and wisdom. Anyone who performs a deed because of an astrological calculation or arranges his work or his journeys to fit a time that was suggested by the astrologers is [liable for] lashes, as (Vayikra 19:26] states: “Do not tell fortunes.”
A few laws further, Maimonides explains that all the so-called wisdom of astrology is in fact foolish:
All the above matters are falsehood and lies with which the original idolaters deceived the gentile nations in order to lead them after them. It is not fitting for the Jews who are wise sages to be drawn into such emptiness, nor to consider that they have any value, as [implied by Bamidbar 23:23]: “No black magic can be found among Jacob, or occult arts within Israel.” Similarly, (Devarim 18:14) states: “These nations which you are driving out listen to astrologers and diviners. This is not [what G-d… has granted] you.”
Whoever believes in [occult arts] of this nature and, in his heart, thinks that they are true and words of wisdom, but are forbidden by the Torah, is foolish and feebleminded. He is considered like women and children who have underdeveloped intellects.
The masters of wisdom and those of perfect knowledge know with clear proof that all these crafts which the Torah forbade are not reflections of wisdom, but rather, emptiness and vanity which attracted the feebleminded and caused them to abandon all the paths of truth. For these reasons, when the Torah warned against all these empty matters, it advised (Devarim 18:13): “Be of perfect faith with G-d, your Lord.”
Perhaps it can be said that Maimonides’s prohibition is an anachronism and that though he declares it to be a biblical prohibition, he is aware that in Talmudic times it was not considered as such. The reason for the change—according to Maimonides—is that once one becomes aware—as he has in his days—that their words are nonsense, it becomes forbidden just as other similar forms of superstition would be prohibited.
It can perhaps be said that the axiomatic difference between Bar Hiyya and Maimonides is the manner in which they look at the statements of Talmud and the trust that they put in their words. Indeed, when Bar Hiyya wishes to prove that astrology has merit, he states that the reason why he includes a discussion of astrology is: “as I saw from the words of our Rabbis of blessed memory, that they do not invalidate this wisdom and say that it is false. However, from their words it seems that they admit to it.”
What Bar Hiyya does in the letter is demonstrate that the sages believed in this science and express that indeed our forefather Avraham himself—according to the Medrash—followed its wisdom. For him, this is the greatest proof that the science is indeed authentic.
Not so with Maimonides, who takes the polar opposite approach. First, he examined whether or not the science is logically sound. Upon concluding that it isn’t, he states that one should not consider the opinions of astrology. Only towards the end of the letter does he feel the need to reconcile that although he says it is nonsense, the sages seem to believe in it. Rather than say that if the sages say it must be true, he is not apprehensive to say that either their words hinted to something else or they were wrong.
Maimonides sees truth and then reconciles his truth with the Talmud, while Bar Hiyya found his truth from the Talmud. Maimonides’s stance regarding astrology is diametrically opposed to that of Bar Hiyya. Where Bar Hiyya sees wisdom, Maimonides sees superstition. Where Bar Hiyya sees the fulfillment of Torah, Maimonides sees its destruction.
Essentially then, there are two axiomatic differences between Maimonides and Bar Hiyya:
One is the reliance that one has on the words of the sages. Maimonides believed that a mere statement of the sages is not enough to prove that a science is true—as the sages relied on the scientific opinions of the time they lived in. However, for Bar-Hiyya a statement from the sages is the best proof that the science is true—as he believed that all their words were Torah, including their statements concerning astrology.
The second point which is somewhat derivative of the first, is the veracity of the science of astrology. While Bar Hiyya sees it as an authentic science, Maimonides sees it as nonsense and superstition.
It is these two focal points that cause the vast difference in their Halachik decision.
Baron, Social and Religious History, 8 1958 pp. 182-183
Bernard R. Goldstein, Astronomy and the Jewish Community in Early Islam, Aleph (2001 No. 1) pp. 17-57.
Dov, Schwartz, Astral Magic in Medieval Jewish Thought (Ramat Gan, 1999).
Shlomo Sela, Abraham Bar Hiyya’s Astrological Work and Thought, Jewish Studies Quarterly, (2005, 12) pp. 128-158
Shlomo Sela, A Newly Identified Essay on Anniversary Horoscope Embedded in Abraham Bar Hiyya’s Astronomical Tables: Hebrew Edition, Translation and Commentary, Aleph (2013 13.1) pp. 27-76.
Shlomo, Sela, Queries on Astrology Sent from Southern France to Maimonides: Critical Edition to the Hebrew Text, Translation and Commentary. Aleph (2004, 4) pp. 89-190.
Stitskin, Leon D. Judaism as a Philosophy, the Philosophy of Abraham Bar Hiyya, New York, 1960.
Wigoder, Geoffrey, Introduction, Bar Hiyya, 1969.
- Shailat, The Letters and Essays of Moses Maimonides (Jerusalem, 1995) 2:474-477
Jeffery L. Rubenstein, Talmudic Astrology, Hebrew Union College Annual (2007) 109-148.
Leon D. Stiskin, Abraham Bar Hiyya’s Personalism and Methodology, Tradition, Vol. 6, No. 2 (1964) pp. 105-113
Meir, Bar-Ilan, Review of: Dov Schwartz, Astrology and Magic in Jewish Thought in the Middle Agers, Kabbala, 7 (2002) pp. 361-384
Rodriguez Arribas, The Terminology of Historical Astrology According to Abraham Bar Hiyya and Abraham Ibn Ezra. Aleph (2001) pp. 11-54
Ronald C. Keiner, The Status of Astrology in the Early Kabbalah, Jerusalem Studies in Jewish Thought (תשמ”ז)
ד. שוורץ, הוויכוח על המגיה האסטרלגית בפרובנס במאה הי”ד, Zion (1993) 141-174.
 Although Bar Hiyya was a pioneer in the field of Jewish astrology, he was not the first. Already a century before Shabbethai Donnolo (913 – c. 982) explained concepts astronomy and astrology in his work Sefer Hakmoni. The success of said work is to the extent that it is mentioned by Rashi the famed Ashkenazic commentator to the Talmud, Eruvin 56a. Additionally extant was the Beraita De’Mazzalot and Beraita De-Shmuel. There seems that there were other “bereitot” in his possession as well. From the fact that Bar Hiyya quotes (Sefer HaIbur, 3:4) a certain Beraita called “Beraita D’R. Ada b. Ahava” it is clear that Bar Hiyya had access to additional material that is no longer extant. For further discussion of what texts would be available to a Jewish thinker of the period see Bernard R. Goldstein, Astronomy and the Jewish Community in Early Islam, Aleph (2001 No. 1) 17-57.
 For much information of the life and philosophy of Avraham Bar Hiyya, see, Sela. Shlomo Abraham bar Hiyya’s Astrological Work and Thought, Stitskin, Leon D. Judaism as a Philosophy, the Philosophy of Abraham Bar Hiyya, New York, 1960. Wigoder, Geoffrey, Introduction, Bar Hiyya, 1969. Introduction to Sefer Ha’Ibbur (London, 1851). It seems though that there is tremendous guess work and that almost all the details of his life rely heavily on speculation. So he was either born is Soria or Barcelona. He was either born in 1065 or 1070. Indeed, even the manner that he came to acquire his erudition of the sciences is merely speculative. For a discussion of his ethical writings and philosophy see צ. בלומברג, תורת המוסר במשנתם של אברהם בר חייא, יוסף אבן צדיק, ואברהם אבן דאוד, תרביץ, ניסן-אלול תשל”ז, Leon D. Stiskin, Abraham Bar Hiyya’s Personalism and Methodology, Tradition, Vol. 6, No. 2 (1964) 105-113 and ש. ויסבליט, רבי אברהם בר-חייא כמפרש המקרא, כתב-עת לחקר המקרא ועולמו, חוברת ג’ תשל”ז 365-369.
 See Josefina Rodriguez Arribas, The Terminology of Historical Astrology According to Abraham Bar Hiyya and Abraham Ibn Ezra. Aleph (2001) 11-54 for a detailed discussion of Bar Hiyya’s contribution.
 Baron, Social and Religious History, 8 1958 pp. 182-183
 See though Shlomo Sela, Abraham Bar Hiyya’s Astrological Work and Thought, Jewish Studies Quarterly (2015, 12) pp. 128-158. Baron, A Social and Religious History, 8:182-184; Sirat, History of Jewish Philosophy, 93-104 and Langermann, The Jews and the Sciences, 11-14.
 Devarim Rabba, 8:6, Yalkut Shimonie, Devarim, 30:940. Though the word used in the medrash is אסטרולג which means astrology, it is pertinent to point out that at that period of time there was no differentiation made between the word astronomy and astrology.
 His interlocutor, Rabbi Judah b. Brazillai on the other hand was well known as a Halachic sage and was the author of a Halachik work entitled Sefer Ha-Ittim.
 Interestingly, in his preface to his work Tzurat Ha-Aretz, Bar Hiyya insinuates that it is only proper to study astronomy after “one prefaced the learning of Torah to the best of his ability.” Surely he himself was careful to follow his own clause and it is therefore obvious that he had a thorough familiarity with Judaic texts.
 Another individual that calls into question Bar Hiyya’s Halachik authority is RaVaD (HaShlishi) in his work Kasuv Shem, Jerusalem (1979)—a work written against the Talmudic explanations of Rabbi Zerachya HaLevi. There (Pg. 37, Rosh HaShana 20b), he writes: “After these words, and after this whole commentary, and the scent that he smelled from the Kuzari and R. Avraham bar Hiyya the Spaniard…he surrounds himself with adornment that is not his. We should not learn from the words of individuals that were not Talmudists—for they bend the Halacha to fit their word—when it is not so.” Ravad’s issue with using the words of Bar Hiyya for Halacha, was the inherent problem, that in his eyes, while he was a great astronomer, astrologer and mathematician, he was not a Talmudist.
 On the other hand, it does seem that this letter by Bar Hiyya affected later defenses for astrology and indeed Halachik practice until today. The author of the Shulchan Aruch, Rabbi Yosef Karo explains in his commentary to the Tur (Tur, Yorah Deah 179) his opinion, that contrary to Maimonides that forbids all astrology, there are certain actions that are permitted and not considered “asking Chaldeans.” Indeed, to bolster his claim, he brings the responsa literature of Nachmanides (#283, See יעקב הלוי ליפשיץ, תשובה שאלה רמב”ן על עניין המנחשים והמכשפים ובענייני החוזים בכוכבים, צפונות ד, עמ’ ו-טז). This responsa makes similar differentiations as Bar Hiyya and employs similar proofs and logic. It is not farfetched that Nachmanides saw Bar Hiyya’s work and relied on it when authoring his own response. That Nachmanides was familiar with Bar Hiyya’s work is clear from his Derashat Torah Temima, (Israel, 2005) pg. 480 where he brings the explanation of סחיב אשורטא (Sachiv Ashurta) which was an honorific for Bar Hiyya. Being that he knew an obscure explanation from Bar Hiyya and called him an honorific showing that he was familiar with his work, it is not farfetched to assume that he knew of his responsa about astrology as well. Additionally Meiri (בית הבחירה על מסכת סנהדרין, מהדורת א’ סופר, ירושלים תשכ”ה עמ’ 243-267) brings in his defense of astrology many points that are reminiscent of Bar Hiyya’s argument. It seems than that Bar Hiyya’s work affected the thought process of Jewish thinkers in subsequent generations.
 Hebrew text, ed. G. Wigdor 1971. English Translation, G. Wigdor 1969
 Talmud, Pesachim 113b
 That he was a teacher of the sciences is clear from his statement: “From my youth on, I have been busy learning, dealing with, inquiring and teaching the science of the stars (Chochmat Ha-Kochavim).”
 Unless the protest came from a greater authority of Jewish Law. This is perhaps additional support that the detractor was Judah b. Brazillai. See later in the paper for further discussion.
 Translation from Shlomo Sela, Abraham Bar Hiyya’s Astrological Work and Thought, Jewish Studies Quarterly, (2005, 12) pg. 129.
 One can possibly comment on his authority as a Talmudist and Halachik authority from his statement in his philosophical work Sefer HiGayon HaNefesh, Ha-Amud HaRevi-I, Pg. 32 (Jerusalem, 1967). “So anyone who believes that after his death he can be benefited by the actions—in his merit—of his sons and his people and their prayers for him, is harboring false ideas. It is a false hope in the eyes of all scholars and men of knowledge… For, we do not find in the Torah any citation from which we can derive that any action of the living in this world can benefit the dead.” However, a brief look at Talmudic and Medrashic sources do indeed express that the prayers of the living can affect the dead. Included in Talmudic sources that express that the child can improve the father and vice versa are Talmud Sota 10b concerning the prayers of Dovid for his son Avshalom. Jerusalem Talmud, Sanherdin 11:5 concerning various prayers of the living for the dead. Kalla Rabati Ch. 2, which expresses a Medrash of R. Akiva of the prayers of the living for the dead, as well as Tanna D’bei Eliyahu Ch. 17 that states a similar idea. Clearly then, contrary to Bar Hiyya’s assertion there is ample Torah evidence that suggests that the prayers of the living affect the dead.
 In Maimonides Pirush HaMishnayot, Erchin 2:5 he praises Bar Hiyya’s astronomical calculations, saying: “Already, in Spain an individual complied a work on this topic. It is an extremely beautiful work that there is no work on the topic of Ibbur in the east that is in any way similar.”
 Maimonides, Laws of Kiddush HaChodesh 9:1 and 10:1-7 brings an argument of the sages concerning the length of a year. While “some Sages maintain that it is 365 days and 1/4 of a day, others maintain that it is slightly less than that figure.” They say that a year is (10:1) “365 days, 5 hours, 997 units, and 48 moments.” Indeed, when stating which is more accurate Maimonides states that the second one is, saying (10:6): “It appears to me that [the Sages] relied on this calculation [of the length] of the seasons regarding the institution of a leap year, in the era when the High Court held sessions and would institute a leap year because of the time [when the equinox was scheduled to occur] or for other reasons. For this calculation is more accurate than the former one. It shares a greater resemblance to the data explained by the astronomers than the first opinion, which considered a solar year to be 365 and 1/4 days.” However, while the first opinions is Shmuel’s—as found in the Talmud, Eruvin 56a, the other opinion is not found there at all. Indeed, this opinion is not extant in any Talmudic dialogue at all. Instead, it is found in Sefer HaIbur of Avraham Bar Hiyya, Ma-amar 3, Sha-ar 4. (London) 1851, Pg. 101: “The length of a solar year according to R. Ada b. Ahava when one understands his reasoning—like we saw explicitly in the Beraita with his name is 365 days, 5 hours, 997 units and 48 moments.” There too, he has an extensive elucidation of the calculation—similar to Maimonides—eventually saying (Shar 5) saying that this is the one the sages relied on: “The calculation of R. Ada b. Ahava is accurate.” He postulates that the sages hid the more accurate calculation of R. Ada and instead said the less accurate calculation of Shmuel because the nations at the time were less accurate about their calculations so they therefore hid the calculation passed down for Sinai. It is for this reason, says Bar Hiyya that the Talmud, Kesubos 112b refers to the calculation of the years as “the secret of ibbur,” because they hid the true calculation of R. Ada b. Ahava. Being that the “Beraita of R. Ada” is not extant it is probable to assume that Maimonides first learned of it from the work of Bar Hiyya. Although possible that Maimonides too had access to it, from the similar conversation it seems that he was affected by Bar Hiyya’s work which as expressed above Maimonides highly praised. So while perhaps Bar Hiyya was not a halachik authority in the regular sense, his expertise in astronomy definitely influenced the laws of creating the Jewish calendar.
 See Although S. Sela Avraham Bar Hiyya’s Astrological Work and Thought, Jewish Studies Quarterly, (12) 128-158 for a discussion of many points of the letter from a clarification of many of the astrological frameworks that he uses and a discussion of astrological magic.
 Baron, ibid. See however Shlomo Sela, A Newly Identified Essay on Anniversary Horoscope Embedded in Abraham Bar Hiyya’s Astronomical Tables: Hebrew Edition, Translation and Commentary, Aleph (2013 13.1) pp. 27-76. From the occurrence of this astrological work within the astronomical tables it seems that the division between various fields is not as concrete as Baron suggests.
 Megilat Hamilageh, Berlin (1424) Pg. 111.
 In general it is possible to postulate that Bar Hiyya’s point in the Megilla is to be seen as a polemical defense for the Judaic version of history against Al-Biruni and his ilk. In Al-Biruni’s Chronology of Ancient Nations he discusses and denigrates certain statements about history using the tools of astrological history. (Al-Biruni, The Chronology of Ancient Nations, Trans. C.E Sachau (London, 1979) P. 163.) Bar Hiyya himself, alludes to the controversy regarding astrological history saying: “Everything that you have heard contrary to what we have said, whether it is concerning the flood or concerns other matters, do not rely on it, for these are false claims.” Sefer Ha–Ibbur, (London, 1851) P. 98. For further discussion see Bernard R. Goldstein, Astronomy and the Jewish Community in Early Islam, Aleph (2001 No. 1) 17-57. Possibly it can be said is that Bar-Hiyya is less determined of proving astrological history and more determined to prove that the dates of the Torah are indeed accurate even according to an astrologist. See as well See Josefina Rodriguez Arribas, The Terminology of Historical Astrology According to Abraham Bar Hiyya and Abraham Ibn Ezra. Aleph (2001) 11-54 for a discussion of Historical Astrology according to Bar-Hiyya.
 Shabbos 156a
 Bar Hiyya hints to the name of his patron with the words in the preface to his Sefer Tzurat Ha-aretz “יסגא לעד שלומו, ולפני שמש ינון שמו”. The literal translation of these words are, “May his peace be great for ever and before the sun, his name will be magnified.” Although the literal translation does not express a name, a deeper look at these words perhaps hints to the name of the patron. While the beginning of the blessing “May his peace be great for ever” is not uncommon in Rabbinic literature as it is based on a greeting found in the Talmud (B. Talmud, Sanhedrin 11b, J. Talmud, Berachos 5:1) the second half of the greeting, of “his name will be magnified” is not particular common or often used in conjunction with the first half of the greeting. With this in mind it is possible to see in these words a hint to the name—which is perhaps Shlomo. The reason for this assumption is that it is based on the fact that both the beginning of the expression and the end are connected with this name. The first half of the statement begins “may his peace be great,” the word peace being the translated from the word shlomo—hinting perhaps to the name Shlomo. The end of the blessing as well “and before the sun, his name will be magnified,” is perhaps as well a hint to the name Shlomo. The reasoning is as follows: the words ““and before the sun, his name will be magnified is a direct quote from Psalms (72:17) which is a psalm specifically stated in honor of King Solomon (Shlomo). The beginning of the chapter of Psalms begins (Psalms 72:1) “Concerning Solomon. O G-d, give Your judgments to a king and Your righteousness to a king’s son.” Indeed, an alternative reading to the words “ינון שמו”, “his name will be magnified,” is “his name is Yinon.” I.E. that Yinon which means magnified is an alternative name for Solomon. Based on these two expressions of the word Solomon it seems abundantly clear that the name of the patron is indeed Solomon. Although in certain manuscripts (Vatican #468) the name Avraham b. Shlomo is mentioned it is possible that this was a later addition using a similar logic to what was derived here. Indeed, in the Oxford manuscript (# 19325) and Cambridge manuscript (# 16309) there is no name clearly expressed.
 Shlomo. Sela, Avraham Bar Hiyya’s Astrological work and thought, Jewish Studies Quarterly, 12 (2005) 128-159. It is perhaps this very differentiation that is the important distinction between on one hand his belief in astrology and on the other that he seems to have believe that one who uses it is “asking Chaldeans.” That this is not a clear distinction is perhaps what Bar Hiyya found bewildering.
 Shlomo. Sela Avraham Bar Hiyya’s Astrological Work and Thought, Jewish Studies Quarterly, (12) 128-158, has pointed out throughout Bar Hiyya’s writing there are sprinklings of astrology. However, the astrology found in them is not instructive. That being the case, it can be, that even if Bar Hiyya conceded he did not find issue with astrological ideas found in his other works.
 See, for example, inter alia, Baron, Social and Religious History, 6: 149.
 Shlomo. Sela, Avraham Bar Hiyya’s Astrological work and thought, Jewish Studies Quarterly, (2005 12) pp. 128-159.
 So, though some research makes the claim that Barzillai was against astrology—see for example Ronald C. Keiner The Status of Astrology in the Early Kabbalah, Jerusalem Studies in Jewish Thought (תשמ”ז) p. 15*, his assertion seems to be clearly incorrect as Barzillai’s approach was clearly more nuanced.
 As demonstrated by Sela, ibid. additionally it appears that Judah b. Barzillai is the author of a work entitled Kitzur Tzurat Ha-aretz, which is an abbreviated version of Bar Hiyya’s work which bears the same name.
 Interestingly, there are halachik ramifications of beginning matters during the sixth hour of Friday which is ruled by mars. Rabbi Avraham Gombiner in his famous work Magen Avraham to Shulchan Aruch, Orach Chaim 271:1) sites the opinion of Tikunei Shabbos that one should not recite the Kiddush on the eve of Shabbos between the sixth and seventh hour as that is the time when mars rules. Indeed, this is a widespread custom until today in many communities. See as well צ. לנגרמן, לכוון את השעה, פעמים, סתיו (תשס”א) עמ’ 76-88.
 Talmud, Pesachim 113b. Interestingly, though the Rabbi’s derived this prohibition from a verse, he refers to the prohibition as rabbinic as opposed to biblical.
 As expressed above, the statement that these wisdoms “are illuminated to him like the streets of Naharda’a” alludes to the wisdom of the stars, as expressed conveyed about Shmuel, Berachos 58b.
 See ד. שוורץ, הוויכוח על המגיה האסטרלגית בפרובנס במאה הי”ד, Zion (1993) 141-174.
 See, ד. שוורץ, הוויכוח על המגיה האסטרלגית בפרובנס במאה הי”ד, Zion (1993) 141-174
 Talmud, Shabbos 156a-b. For further discussion see Jeffery L. Rubenstein, Talmudic Astrology, Hebrew Union College Annual (2007) 109-148.
 Devarim 18:13-14.
 While most standard editions of the Torah translate this to mean that they “hearken to diviners of [auspicious] times and soothsayers,” we have left these words in their original Hebrew as the meaning is disputed and is one of the topics of the letter under discussion.
 Interestingly, while Maimonides was vehemently against astrology he did not consider the prohibition derived here to me enumerated in the 613 commandments. Not so Nachamanides—who wrote a defense to astrology (Responsa 283), who does consider this as a commandment among the 613. See HaSagot HaRamban, Sefer HaMitzvos, Positive Commandments #8. It has been suggested (Malbim, HaTorah VeHamitzvah, ad loc) that Maimonides sees this as conditionary to being “whole-hearted with G-d” as opposed to being a positive directive.
 See Shlomo, Sela, Queries on Astrology Sent from Southern France to Maimonides: Critical Edition to the Hebrew Text, Translation and Commentary. Aleph (2004, 4) pp. 89-190. That Maimonides was familiar with Bar Hiyya’s work is clear as seen above. It is therefore not too farfetched to assume that the letters goal is—at least to a certain extent—to negate ideas postulated by Bar Hiyya.
 See the Guide to the Perplexed 3:32 for example that many commandments were instituted to wean individuals away from nonsensical idolatrous practices.
 ד. שוורץ, הוויכוח על המגיה האסטרלית בפרובנס במאה הי”ד, החוברת ההיסטורית הישראלית (1993) עמ’ 145, D. Schwartz, Astral Magic in Medieval Jewish Thought (Ramat Gan, 1999).
 When Bar Hiyya discusses this group he uses the verse Daniel 2:2: “And the king commanded to summon the necromancers, the astrologers, the sorcerers, and the Chaldeans to tell the king his dreams, and they came and stood before the king,” and the verse Shemot 7:11: “[Then,] Pharaoh too summoned the wise men and the magicians, and the necromancers of Egypt also did likewise with their magic.” He explains that the magicians are those whether according to the astrological signs at the present moment one can transform one matter into another. Hence, what is forbidden is not regular astrology, but astrological magic. Interestingly, M. Bar-Ilan, Review of: Dov Schwartz, Astrology and Magic in Jewish Thought in the Middle Agers, Kabbala, 7 (2002) pp. 361-84 asserts that the term astrological magic is either an oxymoron or an anachronism created by modern scholars. In Meir Bar-Ilan, a Review of “John S. Lucas, Astrology and Numerology in Medieval and Early Modern Catalonia, Review of Rabbinic Judaism, 8 (2005) he writes on pg. 289: “People in the Middle Ages were familiar with both astrology and magic, of course, but no such concept of “astral magic” has ever existed, except in the writing of modern scholars.” It seems though—that at least according to Bar-Hiyya—there was an element of astrology that was connected to magic, to the point that their practitioners are referred to as מכשפים or sorcerers.
 This comparison to medicine seems to be intentional—as it is clearly an example of an inexact science that is permitted, or even mandated in the Torah. On the verse (Shemot 21:19) that says, “And to heal he shall heal,” The Talmud (Bava Kama 85a) cooments: “The School of R. Yishmael taught: [The words] “And to heal he shall heal’’ [are the source] whence it can be derived that authorization was granted [by G-d] to the medical man to heal.” Although the science was not exact one may nevertheless consult a doctor. Indeed, Rashi, the foremost commentator to the Talmud, explains that this means that a person should not say: “the merciful one makes sick and He heals as well.” This seems as well—according to Bar Hiyya—to correlate to astrology that a person should not merely rely on the Lord but instead should within nature listen to the words of the wise.
 Tehillim 34:15.
 Maimonides, Letter on Astrology. Though the authenticity of the letter has been questioned by Herbert A. Davidson, The Authenticity of Works Attributed to Maimonides, Me’ah She’arim, Studies in Medieval Jewish Spiritual Life, pp. 111-133, I. Shailat, The Letters and Essays of Moses Maimonides (Jerusalem, 1995) 2:474-477 defends his authorship. Concerning the letter sent to Maimonides, see Shlomo, Sela, Queries on Astrology Sent from Southern France to Maimonides: Critical Edition to the Hebrew Text, Translation and Commentary. Aleph (2004, 4) pp. 89-190
 Laws of Idolatry 11:9.
 Megilat Hamilageh, Berlin (1424) Pg. 111. He makes the same argument in the letter.