the-astrology-book

Al-Biruni
The Tafhim is a truly remarkable book in several respects. First, it is a medieval
Oriental book dedicated to a woman. This by itself is remarkable. The woman, Rayhana
bint al-Hasan, was a Persian noblewoman who was apparently a student of Al-
Biruni’s while both were semicaptive at Mahmud’s court at Ghaznah. Virtually every
paragraph of the Tafhim is interesting. Al-Biruni seems to have written both an Arabic
and a Persian version. It contains 550 paragraphs plus a colophon that Al-Biruni tells
us was intended as an aide-mémoire for Rayhana in the form of questions and answers.
The 1934 Wright translation deletes this feature and presents a text arranged in paragraphs
with headings. Though Wright’s translation shows signs of incompletion—it is
typewritten, not typeset, with unpolished notes and comments, and clearly paraphrased
in places—the overall composition and handling of the subject shows Al-Biruni to
have possessed a mind of the highest quality and probity. As a teacher he must have
been outstanding. He writes with clarity and conciseness uncharacteristic of medieval
astrological writers. He tells us, at the very end of the book, that he has set forth what a
beginner needs to know about astrology. He exceeds the modern standards in this
regard and provides us with what amounts to an introduction to mathematics, geography,
chronology, and astronomy before finally addressing judicial astrology.
As a textbook on astrology, the Tafhim is on a par with Ptolemy’s Tetrabiblos.
Indeed, it is superior to it, in that it contains a good deal of material contained in
Ptolemy’s Almagest as well. Much of the Tafhim is clearly an attempt to epitomize the
Almagest. Its value is in the scope of its contents. In no other astrological work is there
such a comprehensive survey of medieval astrological science and the subjects that
supported it. The book reveals the many-faceted skills and duties of an eleventh-century
Persian astrologer. Al-Biruni is also interested in the Hindu astrological traditions
and how they differ or coincide with those with whom he is familiar. He also reports
Magian astrological practices. The shortcoming of the book is that, written as an aidemémoire,
it lacks examples showing how to apply the methods, astrological or mathematical,
so thoroughly set forth. However, the book does provide a uniquely clear window
into the level of knowledge attained by a Persian astrologer in 1029. By comparison,
his European counterparts were deprived.
Al-Biruni’s exposition of astrology places the subject squarely in the context of
the mathematical disciplines. He begins by introducing the student to geometry and
arithmetic to provide the would-be astrologer with the ability to calculate. The calculations
are pre-logarithmic, and geometrical trigonometry is used. Curiously absent is
any mention of the forty-seventh proposition of Euclid, also known as the Pythagorean
theorem, which Ptolemy used to such good effect in the first book of the Almagest
to find the lengths of chords subtending arcs of the circle.
Al-Biruni’s discussion of arithmetic is Pythagorean, based clearly on Nicomachus’s
Introduction to Arithmetic. Initially, this seems strange and possibly even esoteric,
until one realizes that ancient calculation in the Middle East, insofar as it was
based on Greek mathematics, was based on theoretical arithmetic such as Nicomachus’s.
As late as the thirteenth century, this was still true in Europe. For instance,
Guido Bonatti, in Liber Astronomiae, asserts that the art of calculation has to do with
the knowledge of numbers and tables, such as the multiplication tables and tables of
roots and powers either found in Nicomachus’s work or suggested by him. In practice,
THE ASTROLOGY BOOK
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