TODAY JOHANNES THOMANN (by Prof. Charles Burnett)

Johannes Thomann is a Research Fellow and Librarian at the Institute of Asian and Oriental Studies at the University of Zurich ( He has written extensively on medieval physiognomy in the Sanskrit, Arabic and Western traditions, on the history of astronomy, and on the depiction of astronomical events in art.

ChB: Could you tell us the main trends and aims in your research in Islamic astronomy?

JTh: In the near future I intend to publish an edition of Arabic astronomical documents preserved in papyrological collections in Vienna, Strasbourg, Berlin and Florence. These are mainly horoscopes, ephemerides, almanacs and some fragments from codices. They date from the 9th to the 13th centuries and are first hand witnesses of astronomical practice in this epoch. In a second project I am editing an Arabic commentary on books IX to XIII of Ptolemy’s Almagest which has been attributed to al-Farabi. In parallel to this text I will edit also  Ishaq Ibn Hunayn’s translation of the Almagest (books IX to XIII), which was the textual basis of that commentary. Further I am editing the two versions of astronomical tables by Habash al-Hasib.

ChB: From your experience, how was the astrolabe used in the Islamic Middle Ages?

JTh: In Baghdad, the centre of the Islamic realm from the mid-eighth century onwards, the astrolabe played a crucial role in teaching at the beginning of the 9th century and later. The size of early astrolabes was very small and they were not suitable for productive tasks in astronomy since they were not sufficiently precise. The great number of treatises and their content with basic exercises makes it likely that they represent the standard procedure of introductory teaching in astronomy.

ChB: How was teaching with the astrolabe integrated with the use of other texts in a curriculum in astronomy?

JTh: It seems that there was a three step development in teaching astronomy in Baghdad. The oldest Arabic texts of the 8th century were in verse and used for memorising. This was the Indian method of learning since all known Sanskrit work of the sixth to the eighth centuries were in verse too. These contain also chapters on the use of astronomical instruments. However, the plane astrolabe became known in Baghdad from Greek and Syriac sources, and became the main teaching tool in astronomy. Texts on the use of the astrolabe are written in an instructional style, often in imperative form. They give the impression of astronomy lessons of a master to his pupil. It took some time before the Almagest became a textbook in teaching. The context was different from the earlier works. The commentary of al-Farabi (or of one of al-Farabi’s colleagues) shows that astronomy was taught within a philosophical curriculum which culminated in the topic of metaphysics. In this context, technical aspects of astronomy were not important, but emphasis was given to the description of geometrical models.

ChB: If astrolabes were solely used as teaching instruments, why do we have such well-made and expensively produced specimens from the Islamic world?

JTh: The one  example from from early Abbasid time (9th century) is significantly different in size and perfection from the beautiful instruments made in later times. It was suitable as an tool for exercise and demonstration, but hardly useful for serious astronomical tasks.

ChB: How long did the astrolabe continue to be used in the Islamic world?

JTh: Two horoscopes on a piece of paper in the library of Zurich dating from late 19th century and probably produced in Skopje contain the degrees of the houses, and after testing a number of methods I came to the conclusion that an astrolabe was used to calculate the positions of the houses. This would be a very late use of an astrolabe for real astronomical practice.

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

JTH: This is a real desideratum. There are substantial studies on the impact of the astrolabe in Latin Europe. There are many studies on the astrolabe in Muslim societies. Therefore, investigations on the role of the astrolabe in Jewish society are likely to provide precious insights into the practice and teaching of science in general and the way scientific concepts travelled across linguistic and religious boundaries in particular. Astrolabes are very condensed pieces of information and strongly linked both to astronomical theory and its practice. In their design they are part of the tradition of material culture and, at the same time they are an offspring of scholarly literature. In that sense, the astrolabe is a unique topic in cultural history and deserves more attention.

 Thanks for this Johannes!

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