| From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 556-557 |
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Ibn al‐Haytham: Abū
ʿAlī al‐Ḥasan ibn al‐Ḥasan
Y. Tzvi Langermann
Alternate
names
Alhazen
Born Basra (Iraq),
965
Died Cairo (Egypt),
circa 1040
Ibn
al‐Haytham (often referred to in the literature as Alhazen, the Latin
version of al‐Ḥasan) was one of the most important and influential
figures in the history of science. He wrote on topics that included logic,
ethics, politics, poetry, music, and theology (kalām), and produced
summaries of Aristotle
and Galen. His extant works are mostly on mathematics, optics, and astronomy.
As a young man, Ibn al‐Haytham moved to Egypt from Iraq and was involved
in an abortive engineering project in Egypt on regulating the flow of the
Nile. The sources do not agree on the details of the story; however, it is
clear that after this brief try at government work, Ibn al‐Haytham chose
a life of quiet scholarship. He earned his living copying scientific manuscripts,
and carried out extensive research and correspondence in philosophy and the
sciences.
In
his youth Ibn al‐Haytham inquired into the different religions and came
to the conclusion that the truth is one. This fundamental insight of gaining
favor with God by seeking knowledge of the truth underlies some of his most
important scientific activity. Specifically with regard to astronomy, Ibn
al‐Haytham was troubled by inconsistencies in the treatment of problems
of interest to astronomy and two other disciplines, natural philosophy and
optics. His most repercussive writings critically examine the issues and propose
solutions.
At
least since Aristotle, it has been taken for a fact that the motions of the
celestial bodies are uniform and circular, and that the stars are embedded
within a set of concentric spheres. However, astronomy had progressed much
in the intervening centuries; in particular, the Almagest, Ptolemy's
landmark text, had set out a theory far more detailed and complex than anything
Aristotle had proposed. True, Ptolemy himself had tried to give a physical
account in his Planetary Hypotheses. However, no one was quite sure
how all the pieces fit together. Moreover, some of the mathematical devices
that Ptolemy had employed, for example, the equant or lunar prosneusis, were
in direct violation of the principle of uniform circular motion about a fixed
center.
Ibn
al‐Haytham addressed these issues in a number of his writings. In his
al‐Shukūk ʿalā
Baṭlamyūs (Doubts concerning Ptolemy),
a thoroughgoing critique of the Almagest, Planetary Hypotheses, and
Optics, he showed in great detail where and how Ptolemy had violated
the principles of natural philosophy. An early monograph, which does not survive
but which is mentioned in a later defense of his views and is summarized by
Naṣīr al‐Dīn al‐Ṭūsī, attempts to provide
a physical solution for one of the knottiest problems, the motion called iltifāf,
which was produced by Ptolemy's models for the motion in latitude of the planets.
Fī
Hayʾat al‐ʿālam (On the configuration
of the world) is perhaps Ibn al‐Haytham's most ambitious effort in this
area of research; it certainly was his most influential astronomical writing.
Like other books of the genre known as hayʾa (a cosmography of
the Universe), Ibn al‐Haytham's treatise explains basic astronomical
concepts (e. g., longitude, latitude, and altitude) and discusses mathematical
geography. This work proposes to match the geometry of mathematical astronomy
to the three‐dimensional picture endorsed by natural philosophy, so
that the reader will be aware of the identity between the two systems. However,
Ibn al‐Haytham does this only schematically. That is to say, in each
of the chapters devoted to the planets, he first describes the three‐dimensional
orbs, moving inward from the planet to the center of the Earth; this is the
depiction of natural philosophy. Ibn al‐Haytham then reverses this description,
this time showing how these orbs are in fact the intersections of the three‐dimensional
bodies with the planes of the circles produced by either the planet or devices
such as the center of the epicycle; these are the geometrical constructs of
the astronomers. Note that the outstanding problems of celestial physics –
those elucidated in detail in the Doubts – are left unresolved. Nonetheless,
On the Configuration does give a consistent report in which both the
philosophical and the mathematical accounts harmonize. As noted above, the
book was widely repercussive, especially in translation; two different Latin
translations are extant, and no less than five different Hebrew translations
have been identified.
The divergences
between the physical and the mathematical accounts were fundamental, and their
resolution required a rethinking of astronomical modeling. Ibn al‐Haytham
provided only basic direction in this matter; however, his influence is felt
on later people, most notably Naṣīr al‐Dīn al‐Ṭūsī,
who worked toward a fuller resolution of the issues.
The
conflicts between astronomy and optics were far less serious, affecting only
some specific problems. The so called Moon illusion, i. e., the apparent
enlargement of celestial bodies and the distances between them when they lie
low on the horizon, occupied Ibn al‐Haytham's attention throughout his
career. In his youthful commentary to the Almagest, he endorsed and
even provided with “proof” Ptolemy's remarks that the enlargement is produced
by refraction through the Earth's “vapors” (i. e., atmosphere), similar
to the way bodies immersed in water are magnified. In a later monograph devoted
exclusively to this topic, Fī Ruʾyat al‐kawākib
(On seeing the stars), he distanced himself somewhat from Ptolemy's explanation.
In his masterful compendium al‐Manāẓir (Optics) Ibn al‐Haytham correctly identified
the problem as one belonging to the psychology of perception, though he did
allow that thick vapors could sometimes be a secondary factor.
Ibn
al‐Haytham's writings are distinguished by a clarity of exposition and
originality of approach. He contributed to the technical literature on astronomy,
but at the same time he strove to make astronomical knowledge accessible to
a wider public. On the Configuration employs minimal mathematics. It
could thus be understood by philosophers, the audience most troubled by the
discrepancies between mathematics and physics; this is probably one reason
for its great success. Ibn al‐Haytham's commentary to the Almagest,
unlike other commentaries that had been written before, aimed to clarify obscure
points for the beginner. His monograph Fī Kayfiyyat al‐arṣād (On the method of
[astronomical] observations) offers a historical explanation, unique in medieval
literature, of how astronomical theory was built on observation.
Ibn
al‐Haytham also authored several monographs on isolated problems, such
as the determination of the meridian and of the qibla (i. e.,
the direction of Mecca), sundials, and the visible appearance of the lunar
surface.
Selected References
Kennedy, E. S. (1989). “Ibn al‐Haytham's Determination
of the Meridian from One Solar Altitude.” Zeitschrift für Geschichte der
Arabisch‐Islamischen Wissenschaften 5: 141–144. (Supplies a proof
for Ibn al‐Haytham's method; Arabic texts of two treatises on determining
the meridian line by Ibn al‐Haytham were edited by Fuat Sezgin in Zeitschrift
für Geschichte der Arabisch‐Islamischen Wissenschaften 3 (1986):
7–43 [Arabic numeration].)
Langermann, Y. Tzvi (1990). Ibn al‐Haytham's On
the Configuration of the World. New York: Garland. (Arabic text, English translation,
introduction and notes.)
Ragep, F. Jamil (2004).
“Ibn al‐Haytham and Eudoxus: The Revival of Homocentric Modeling in
Islam.” In Studies in the History of the Exact Sciences in Honour of David
Pingree, edited by Charles Burnett, Jan P. Hogendijk, Kim Plofker, and
Michio Yano, pp. 786–809. Leiden: E. J. Brill. (Provides Ṭūsī's
summary of Ibn al‐Haytham's treatise on iltifāf.)
Sabra, A. I. (1972). “Ibn al‐Haytham.” In Dictionary
of Scientific Biography, edited by Charles Coulston Gillispie. Vol. 6,
pp. 189–210. New York: Charles Scribner's Sons. (Reliable summary and full
bibliography up to circa 1970.)
——— (1977). “Maqālat
al‐Ḥasan ibn al‐Ḥasan ibn al‐Haytham fī
al‐athar al‐ẓāhir fī wajh
al‐qamar” (Ibn al‐Haytham's “Treatise on the Marks Seen on the
Surface of the Moon”). Journal for the History of Arabic Science 1:
166–180.
——— (1978). “Maqālat
al‐Ḥasan ibn al‐Ḥasan ibn al‐Haytham fī
kayfiyyat al‐arṣād” (Ibn al‐Haytham's “Treatise on
the Method of [Astronomical] Observations.”) Journal for the History of
Arabic Science 2: 155, 194–228. (Arabic text with English synopsis.)
——— (1979). “Ibn al‐Haytham's
Treatise: Solutions of Difficulties Concerning the Movement of Iltifāf.”
Journal for the History of Arabic Science 3: 388–422. (Arabic text
with English synopsis.)
——— (1987). “Psychology
versus Mathematics: Ptolemy and Alhazen on the Moon Illusion.” In Mathematics
and Its Applications to Science and Natural Philosophy in the Middle Ages,
edited by Edward Grant and John E. Murdoch, pp. 217–247. Cambridge: Cambridge
University Press.
——— (1995/1996). “On
Seeing the Stars, II: Ibn al‐Haytham's ‘Answers’ to the ‘Doubts’ Raised
by Ibn Maʿdān.”
Zeitschrift für Geschichte der Arabisch‐Islamischen Wissenschaften
10: 1–59.
——— (1998). “One Ibn
al‐Haytham or Two? An Exercise in Reading the Bio‐bibliographical
Sources.” Zeitschrift für Geschichte der Arabisch‐Islamischen Wissenschaften
12: 1–50. (A thorough reexamination of the writings attributed to Ibn al‐Haytham.)
Sabra, A. I. and A. Heinen (1991/1992). “On Seeing the Stars:
Edition and Translation of Ibn al‐Haytham's Risāla fī Ruʾyat
al‐kawākib.” Zeitschrift für Geschichte der Arabisch‐Islamischen
Wissenschaften 7: 31–72.