Homepage of:

Benno van Dalen

Historian of Science with special interest in Islamic astronomy and transmission between Islam and China, India and Europe.
Former editor of
Historia Mathematica, International journal of history of mathematics.
Research leader in the project Ptolemaeus Arabus et Latinus at the Bavarian Academy of Sciences and Humanities in Munich.

Contents of this page: Research Interests, Links, Address. See also: my curriculum vitae and list of publications.
Recommended escape routes: Description of my computer programs, Links.
To be added some time in the future:
ZijManager, a Windows program for entering, editing and mathematically analysing medieval astronomical tables.

Recent changes on my webpages: This entry page, my list of publications, and my curriculum vitae are more or less regularly updated until all the information will be moved to a new personal webpage associated with my current employer, the Bavarian Academy of Science. PLEASE NOTE MY NEW EMAIL ADDRESS AT THE BOTTOM OF THIS PAGE!

Research Interests

GENERAL RESEARCH INTERESTS: Ancient and medieval astronomical tables and methods of computation. Transmission of astronomical knowledge from the Islamic world to China, India and Europe.


Since May 1, 2013, I am employed at the Bavarian Academy of Sciences and Humanities in Munich. Together with Dr. David Juste, I am research leader of the new 25-year project Ptolemaeus Arabus et Latinus (project leader: Prof. Dr. Dag Nikolaus Hasse, University of Würzburg; commission: History of Science). Main purpose of this project is to make available reproductions, transcriptions and in the end editions of Ptolemy's astronomical and astrological works (including pseudepigrapha) in Arabic and Latin translations. Also further important works from the medieval Ptolemaic tradition will be published and studied, including, among others, commentaries on Ptolemy's works, zîjes and other works heavily influenced by him. Brief information on  Ptolemaeus Arabus et Latinus is already available at the website of the Academy and that of Prof. Hasse. An extensive web interface, through which the reproductions and transcriptions can be accessed with numerous search facilities, will be set up in the coming year.


As part of the project Ptolemaeus Arabus et Latinus, I continue to work on a revised «Survey Of Islamic Astronomical Tables». The original monograph with this title was published by E.S. Kennedy in 1956 (Transactions of the American Philosophical Society N.S. 46-2, reprinted in 1989) and included brief descriptions of little more than 100 Islamic astronomical handbooks with tables (so-called zîjes), extensive abstracts of 12 of these, a classification of the subjects dealt with, and preliminary conclusions concerning the relations between and the developments in the production of Islamic astronomical handbooks. Nowadays, around 250 zîjes are known, of which nearly 150 are extant in more or less complete form, but only very few have been published or investigated in detail.

The revised Zîj Survey will include at least the following:

At the moment around 130 entries of zîjes for the new Zîj Survey are basically ready. They involve investigations of a large number of works that until now have not yet been studied at all and hence provide the first descriptions of the contents of these works.


On the side, I hope to publish my investigation of the achievements of the Muslim astronomers who were brought to China by the Mongols in the early Yuan Dynasty (around 1270). The available sources for this investigation are:

  1. The Huihui-li (c. 1384), a Chinese translation of a presumably Persian astronomical handbook with tables (a so-called zîj), known to have been available in China in the beginning of the Yuan. The Huihui-li is extant in a number of somewhat different versions, apparently all deriving from a restoration of the original translation carried out by an officer of the Astronomical Bureau of the Ming dynasty in 1477.
  2. The Sanjufînî Zîj, an Arabic astronomical handbook written for the Mongol viceroy of Tibet in 1366.
  3. An Arabic or Persian manuscript at the Pulkovo Observatory (near St. Petersburg in Russia), which was obtained in China in the 19th century and contains only a small set of astronomical tables.
Although the sources 1 and 2 are obviously two different works, a mathematical investigation of their planetary tables shows that they must be based on a common predecessor. It turns out that the two sources share values for most of the planetary parameters which are not found in any other Arabic or Persian astronomical handbooks (including those resulting from the extensive observational program at the contemporary Ilkhan observatory in Maragha). It is therefore probable that their common predecessor was a work compiled by the Muslim astronomers who were active at the official Islamic Observatory in the Chinese capital Beijing. The presence in one of the extant versions of the Huihui-li of a large star table independent of Ptolemy's table in the Almagest also points to original, hitherto unknown Islamic observations.
        According to a description published in 1882, the manuscript listed above as source no. 3 is very probably a partial copy of the original work on which both the Huihui-li and the Sanjufînî Zîj are based. Unfortunately, the present whereabouts of the manuscript are unknown; it may have been destroyed by the fire in the Pulkovo Observatory in early 1997.
        At the moment I am working on an edition and English translation of, and extensive commentary on, the Chinese text of the Huihui-li, which will be published as a monograph


During my doctoral research (under the supervision of Prof. Dr. Henk Bos and Dr. Jan Hogendijk of the Mathematical Institute of Utrecht University, Netherlands) I concentrated on the development and application of statistical and numerical tools for the analysis of ancient and medieval astronomical tables. In a number of examples in my doctoral thesis Ancient and Mediaeval Astronomical Tables I used these tools to derive the mathematical structure and underlying parameters of a number of tables which had thus far defied explanation.
        Furthermore, I wrote user-friendly computer programs for DOS-PC, by means of which various tasks frequently occurring in research on medieval astronomy can be conveniently carried out. These include: sexagesimal calculations (also with trigonometric functions); calendar conversions; input, analysis and output of trigonometric, spherical-astronomical, and (pseudo-linear) mean motion tables as they occur in Ptolemaic astronomy.
        During a stay at the Institute for History of Science in Frankfurt am Main (Germany) in 1997/1998 I developed a computer database of parameter values occurring in medieval Islamic astronomical texts and tables. This database relies heavily on the hand-written parameter file of Prof. E.S. Kennedy. It includes parameter values directly quoted in primary and secondary sources, as well as values «squeezed» or otherwise estimated from tables.



Benno van Dalen
Ptolemaeus Arabus et Latinus
Bayerische Akademie der Wissenschaften
Alfons-Goppel-Strasse 11
80539 München


Most recent modification: September 10, 2013.