Dr. Shlomo Sela  is a lecturer in the Departments of Jewish Thought at Bar-Ilan University (Israel).  His research focuses on Jewish attitudes toward the sciences, with special interest in the history of astrology in the Middle Ages. He is an expert in Jewish astrology, notably Abraham ibn Ezra’s astrological treatises, which he is editing and translated for Brill.


Plate with the divisions of the twelve astrological houses and latitude scratched in Hebrew (Science Museum, London)

Plate with the divisions of the twelve astrological houses and latitude scratched in Hebrew (Science Museum, London)

JRA: What can be the interest of studying medieval astrology and more specifically Jewish medieval astrology?

ShS: Horoscopic astrology was most probably invented in the late second or early first century BCE, on the basis of Aristotelian physics, Greek cosmology, and Hellenistic astronomy, although it also drew on elements from ancient Babylonia and Egypt. Thus, studying medieval astrology affords a golden opportunity for both scholars and laymen interested in the history of science to observe how the achievements of these branches of Greek science were received, assimilated, applied and developed further in medieval societies and cultures. Jewish medieval astrology is only one case of the aforementioned cultural phenomenon, and for students of the history of science its study is as interesting and fascinating as the study of its reception in the Arab and Latin medieval worlds. However, studying Jewish medieval astrology arouses an intense interest for those particularly interested in Jewish history and culture, mainly because it provides a golden opportunity to ascertain how a traditionalist and conservative culture was transformed by the reception of Greco-Arabic science without losing its religious and national identity.

JRA: What were the relations between astronomy and astrology in the Middle Ages?

ShS: After the rise of Greek science, it is almost commonplace to refer to the close collaboration between astronomy and astrology. Since the practical uses of learned astrology depended heavily on the mapping of the movements and relative positions of the heavenly bodies, it is clear that, on the one hand, horoscopic astrology could develop only after the growth of mathematical astronomy and, on the other hand, that astrology provided a constant stimulus to mathematical astronomy to continue to refine its tools. In addition, the fact that some ancient and medieval prominent scientists grouped astronomy together with astrology in their works highlights their interdependence. In the Middle Ages, a good example of the close collaboration between astronomy and astrology is found in the contents of astronomical tables: along characteristically astronomical topics, such as tables of the mean motions, equations, and true positions of the moon, sun and planets, one may also find typically astrological topics such as tables for casting the 12 horoscopical places at specific terrestrial latitudes, tables of excess of revolution and revolution of the months used in continuous horoscopy, and tables of the planetary astrological ‘nature’ associated to fixed stars.

JRA: Were medieval Jews more interested in astrology than their Muslims or Christians contemporaries?

ShS: This is very difficult to ascertain, and my guess is that Jews were as concerned with astrology as Muslims or Christians contemporaries, and for similar reasons: in an age of extreme insecurity and uncertainty, astrology provided a system of doctrines which, using the state of the art in Greco-Arabic science, claimed to explain and predict human events related to both individuals and collectives.

JRA: Is the astrolabe an instrument characteristic of astrologers?

ShS: One of the main topics of medieval manuals on the astrolabe is to enumerate and explain the functions that this instrument is intended to carry out. Judging by these functions, the astrolabe was a typically astronomical instrument. However, one may also find typically astrological functions, such as the calculation of the cardines and the twelve places of the horoscope or the calculation of the astrological aspects, which are essential and indispensable for the praxis of the astrological métier. From this specific perspective, the astrolabe was an instrument characteristic of astrologers.

JRA: How was astrology accommodated to Jewish culture religion in the middle ages?

ShS: The smooth absorption of astrological content into the hard core of Jewish culture was carried out in two ways: on the one hand, via the incorporation of astrological ideas into the exegesis of classic authoritative Jewish texts, such as the Bible, and, on the other, by the creation in the twelfth century of a comprehensive corpus of Hebrew astrological textbooks that address the main systems of Arabic astrology, thereby providing Jewish readers with access to astrology. From the vantage point of Jewish religion, astrology was seen by opponents of astrology as canceling out the rewards coming from the observance of religious prescriptions, since if individual or collective fate is determined by the stars, it is hard to see how one could maintain an assumption of reward and punishment which would justify the observance of religious commandments. To counteract the utterly deterministic character of astrology, Jewish medieval sympathizers of astrology highlighted the possibility of deliverance from the influence of the stars by virtue of a singular marriage between faith and wisdom: total salvation from the stars occurs when the wise soul of man, after a process of intellectual betterment and religious devotion, departs from his body and enters into conjunction with the glorious God.

JRA: What do you think about this project on astrolabes in medieval Jewish society?

ShS: As Jewish medieval interest in the astrolabe epitomizes the reception of Greco-Arab science into Jewish medieval society, and because this topic is one of the most neglected parts in recent scholarship research focused on Jewish medieval science, the project on astrolabes in medieval Jewish society is in my opinion of enormous importance.

JRA: What main question/s do you think the researchers working in this project should explore or should try to answer?

ShS: After cataloguing, as far as possible, all the extant works composed by Jews in Hebrew (and other languages) on the astrolabe in the Middle Ages, these are some of the questions that in my opinion should be explored: How were these manuals on the astrolabe organized and shaped? Are they essentially the same or in some way different from medieval Arab or Latin manuals on the astrolabe? On which scientific sources did the authors of these manuals draw? Which original contribution, if any, did these texts make? Are there any special features which reveal the authors’ unique contribution and special personality? What linguistic strategy did the authors of these works adopt when faced with the need to create a new Hebrew scientific vocabulary about the astrolabe? How may be explained this enduring Jewish interest on the astrolabe during the Middle Ages and this continuous stream of Hebrew compositions on the astrolabe?

 Thank you, Shlomo. This has been an illuminating interview!