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!





Charles Burnett ( is Professor of the History of Islamic Influences in Europe at the Warburg Institute (University of London) and is part of the research group working on astrolabes in medieval Jewish society. He is an expert in the diffusion of Arabic knowledge into Latin and is also interested in the role of Jews as mediators in this transfer. He has an impressive record of publications on the subject of this transmission and its cultural context, as well as editions and translations of several of the key manuscripts involved in the amazing transfer of knowledge and ideas that took place in western Europe.

Our question for him is to explain the cultural context in which astrolabes emerged in Europe. This is his answer:

We have the first indications of the introduction of the astrolabe into Christendom towards the end of the tenth century in Catalonia, the provenance of the earliest astrolabe to be inscribed with Latin inscriptions, and of the earliest Latin texts. These were based on Arabic texts, some of which have been identified. But a Latin scholar added an elaborate preface, which, after emphasising the importance of the knowledge of astronomy, advertises the significance of the new instrument—the astrolabe–in the following words: ‘Among the other famous instruments of this art provided by him (Ptolemy), he invented  a certain instrument, both most useful for learners and a great miracle for those looking at it, than which among all inventions nothing is more eminent for the intimate investigations of doctrines and the arts of mathematics, and nothing is more useful for investigating the whole of that higher machine and for all astronomical studies and the science of geometry. It is the Wazzalcora, obtained by a divine mind, which in Latin means “flat sphere”, which also by another name is called “the astrolabe of Ptolemy”. In this Wazzalcora, the whole form of the celestial sphere is described by a natural reasoning according to the roundness of the sphere, and all things are noted correctly by the architectonic reasoning of celestial figurations, which I will describe a little more clearly afterwards. How useful this is, both what follows will demonstrate and the truth of the matter will prove’. From this time onwards the astrolabe gained a prominent place in Western European science, as a teaching instrument, as an instrument of observation, and as a symbol of the universe, and of the power of the ruler who owned that symbol. Adelard of Bath addressed a work on the astrolabe to Henry Plantagenet (the future King Henry II of England), pointing out that it was a guide to the universe; for just as the householder should know the house that he lived in, so the dweller in the universe should know his dwelling place, or else be cast out of it. Peter Abelard and Heloise named their son ‘Astrolabius’, perhaps as an indication that he pointed the way to the heavens. Works on the construction and use of the astrolabe featured prominently in the translation programmes from Arabic into Latin of the mid-twelfth century. Through the astrolabe the positions and the names of the most prominent fixed stars in the sky became known. No astronomer or astrologer could be without his astrolabe, and even the schoolboy was expected to know how to use the instrument, as we see from Chaucer’s English text on the astrolabe addressed to his son Louis.

(Sources: José-Maria Millàs Vallicrosa, Assaig d’història de les idèes fisiques i matemàtiques a la Catalunya medieval, Barcelona, 1931; Arianna Borrelli, Aspects of the Astrolabe, Stuttgart, 2008; Geoffrey Chaucer, A Treatise on the Astrolabe Addressed to his Son Lowys A.D. 1391, ed. W. Skeat, London, 1872).


New section on our blog: INTERVIEWS WITH THE EXPERTS

From now on we intend to post regular short interviews  with experts in the fields of the history of science, Jewish history, Jewish science, and astrolabes, the fields in which our research project fits.


Prof. Silke Ackermann ( has been a curator at the British Museum for more than fifteen years, period in which she was in charge of the scientific collections (among them astrolabes). Whilst she was working at the British Museum Silke got involved in setting up the Jewish Astrolabe project and participated as co-investigator. However, her new job as president and professor of the Baltic College (in which she has introduced a MA in Cultural Tourism) separated her from her initial role in our project. Nevertheless, she remains interested in this research and is a member of the board of advisors. Thus Prof. Ackermann and the researcher of the project, Dr. Josefina Rodríguez-Arribas, studied together in August 2012 one of the astrolabes considered in this research (a 11th century Muslim astrolabe with Hebrew inscriptions preserved in the Staatsbibliothek zu Berlin – PK). It is a great pleasure to count on her experience and expertise with scientific instruments. For this reason, we have decided to start this new section of our blog with her.

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Detail of  the back with Hebrew inscriptions of the Andalusian astrolabe at the Staatsbibliothek zu Berlin – PK


JRA: What is an astrolabe? Were astrolabes common objects in the past?
SA: An astrolabe is one of the most sophisticated instruments ever constructed before the invention of the computer – and at the same time it is relatively easy to use. Basically it is a two-dimensional projection of the three-dimensional celestial sphere – similar to a map being a projection of the earth. It can be used in many different ways, for example to tell the time during the day and at night-time, to estimate the time of sunrise and sunset, to determine the time of prayer in the Islamic World, to make certain astrological predictions, to measure angles etc. etc. to name but a few of the manifold uses.
About a thousand astrolabes are known to have survived, many more will have been constructed according to treatises written in various languages from Greek and Latin to Arabic and Hebrew as well as English, French, German, Spanish, Italian and others. They were mostly made of brass and thus very costly (and thus very special) at the time, but we also know of designs for instruments that could be cut from paper and then pasted onto card or wood – a kind of make-yourself version. These will have been more common and used by different people for various functions.

JRA: There were many scientific instruments before the Scientific Revolution of the 17th century. Can you mention some of them for our blog? What is distinctive of astrolabes in relation to all of these instruments?
SA: If one looked at astronomical instruments alone or even just time-keeping instruments there were, indeed, quite a number before the Scientific Revolution such as sundials of virtually infinite designs, quadrants and nocturnals to name but a few. The intriguing feature of an astrolabe is that it combines so many functions and that its basic designs remained virtually unchanged for nearly 2,000 years.

JRA: Why are there astrolabes engraved with different languages? Leaving aside the languages, are there other differences among the extant astrolabes or all of them are similar except for the script?
SA: Astrolabes are truly cross-cultural. The ancient Greeks are credited with the invention of the instrument (or rather: with the discovery of certain mathematical principles that allowed its construction). But the instrument was further developed and used by virtually all cultures that came into contact with it. This is why so many different languages can be found on one instrument, such as the star-names in Arabic or a Latinized forms of Arabic (or a vernacular thereof) of even different languages together when an instrument was for example made in the Islamic World and later used by a Latin scholar who may have added some features in Latin or another who added Hebrew markings. The different languages often tell us the most intriguing stories about an instrument’s history.
There are certain basic features every astrolabe possesses – but many features can be added or omitted at will. Additionally astrolabes can be of the most intricate design and a pure joy to behold – which must be one of the reasons why so many have survived even at a time when they were long out of use. They are just utterly beautiful and from very early on became collectors’ pieces.

JRA: Astrolabes seem to have been known in Europe, Northern Africa, the Near East, and India. Did other cultures like the Far East or pre-Colombine America have astrolabes or similar objects?
SA: I have so far not come across genuine instruments from the Far East or pre-Columbian America, but that does not mean that they do (did) not exist.

JRA: You have been a curator of scientific instruments at the British Museum for many years and now you are teaching at the Baltic College in Schwerin (Germany). What is the interest of studying astrolabes (pre-modern instruments) in the 21st century? Are you able to bring the subject of astrolabes and their historical background into class? How?
SA: In my current role at the University of Applied Sciences at Schwerin in North-East Germany I have so far had very little opportunity to discuss astrolabes. But I am trying to introduce students to the role of objects as historical sources on a par with written documents. The study of astrolabes enables us to bring long-gone periods such as the Middle Ages or the Renaissance to life, to shed a light on the in-depth knowledge of astronomical and mathematical features and on the intercultural exchange that took place.

JRA: We know that you are also very interested in Jewish astrolabes. Your interest in Judaism, where does it come from? What has Judaism to do with astrolabes?
SA: I have always been interested in history and in the sharing of knowledge and ideas between the three great religions of the book (namely Judaism, Christianity and Islam). I am fascinated by the way in which cultures influenced by one or more of these religions used, adapted and developed this intriguing instrument – and how the instruments and related texts mirror the thought-processes behind this exchange. For many years I have researched the exchange of ideas in the Middle Ages and the Renaissance and it became increasingly clear to me how little I actually knew about the role Jewish scholars had in this process of transmission.

JRA: As an expert in scientific instruments, what is the question about astrolabes and Jews that any serious research on the subject should answer or inquire into?
SA: When I first suggested a research project on the role of the astrolabe in Jewish communities in the Middle Ages it was born out of a certain frustration that I could find so little information in my sources and in the literature on what this instrument actually meant for these communities, how it had been used and why and by whom. If the outcome of the project manages to answer some of these questions I would be thrilled.

Thank you!