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Medieval Islamic Astronomy (130/750 -1165/1750)

Jan P. Hogendijk

Dept of Mathematics, Utrecht /KFUPM

May 12, 2011

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Summary of this lecture

1. The sources of medieval Islamic astronomy.

2. Rough outline of the development of medieval Islamicastronomy.

3. Three examples of sources.

4. The universe of the orthodox Islamic theologians.

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Extant sources on medieval Islamic astronomy I

1. More than 100 Zıjes: handbook with tables and instructions.Typically 40 pages of instructions ((250 words per page), 150pages tables.

Surveys: [Kennedy 1956], [King, Samso, Goldstein, 2001].Computer analysis by Benno van Dalen, Frankfurt am Main.

2. Ca. 250-500 ? shorter or longer treatises by astronomers (text,no tables).Surveys: [Sezgin 1978, Rosenfeld and Ihsanoglu 2003]

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Extant sources on medieval Islamic astronomy II

3. Ca. 500-1000 instruments (astrolabes, quadrants, others).

4. Observatories: ruins (Samarkand, Maragha); Jai Singh’sobservatories in Delhi and Jaipur are extant. See [Sayili 1960].

Preliminary catalogue of astrolabes by David King on theinternet. Many instruments rebuilt in Frankfurt, Institute forHistory of Arabic-Islamic Science, see F. Sezgin, Science andTechnology in Islam, Frankfurt 2010, accessible throughwww.ibttm.org, via English, Publications.

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Cultural Context

Development of astronomy stimulated by large-scape patronage bycaliphs and rulers.

Applications:Prediction of astronomical phaenomena, including lunar and solareclipses, first visibility of the lunar crescent.Mathematical geography was part of astronomy. Timekeeping also.Problems inspired by Islam: direction of Makka, prayer tables.

Astronomy was also “applied” in astrological predictions. Therewas much disagreement on the value of astrology.

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Historical Survey I

Early Muslims were already interested in astronomy.see [Heinen 1982]

130/750 - 280/900, Baghdad, Iraq:Assimilation from pre-Islamic Iran, India, Greek;Translations into Arabic(most important work: the Almagest of Ptolemy, ca. 150 CE.)

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Historical Survey II

ca. 200/820: Eastern Islamic world: Beginning of (programs) ofobservations to check and adjust the system of Ptolemy (ca. 150CE). Primarily earth radius and solar theory.

ca. 4th/10th centuries: Advances in mathematics (sphericaltrigonometry etc.), and in observational instruments.

ca. 400/1010 - 800/1400. Eastern Islamic world: Replacement ofsome non-Aristotelian features of Ptolemy’s models byphilosophically acceptable alternatives.

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Three sources I

1. Early period: Al-Battanı (Syria, died 317/929), Zıj(Astronomical Handbook).Published in [Nallino 1899-1907], Arabic text and modern Latintranslation. Ca. 227 pages Arabic text, plus 180 pages numericaltables.Purpose: Prediction of astronomical phenomena: positions of sun,moon, planets; lunar and solar eclipses; first and last visibility ofmoon and planets.Innovations: Computations for the solar orbit.

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Three sources II

2. Abu’l-Rayh. an al-Bırunı (Iran/Turkm/Uzb/Afghanistan, died440/1048)al-Qanun al-Masc udı, in 11 Books, ca. 1200 pages text, 250 pagestables.Perhaps the most brilliant work of Islamic astronomy.Purpose: Theoretical exposition with all proofs.Arabic text published 1954-6 in unreliable edition.Table of contents in English [Kennedy 1971].Uncritical Russian translation: 1976.NEVER translated into a European language.

Al-Bırunı wrote much more: also Kitab al-Tafhım fı Awa’il S. inacatal-Tanjım, Introduction to the First Principles of Astronomy; stillthe best introduction to the field. Available in facsimile withEnglish translation [Ramsay Wright 1934].

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What was in the 11 Books of al-Qanun al-Masc udı?

1. Fundamental cosmological principles; days, years.

2. Chronology and calendars

3. Plane Trigonometry, computation of tables, linear andquadratic interpolation

4. Spherical Trigonometry

5. Geodesy and mathematical geography

6. Time differences between different localities on earth, solartheory, equation of time

7. Lunar motion

8. Eclipses, lunar visibility

9. Fixed stars

10. Planets

11. Astrological computations

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Example from Book I:

Is the earth at rest or does it rotate?

Al-Bırunı says that there were distinguished astronomers in histime who believed in the rotation of the Earth.

He then decides between the values of the earth radius by theGreeks (ca. 6000 km) and the Indians (double) by measuring thedepression of the horizon from a mountain in Pakistan.

He computes the velocity of our motion due to a rotating earth as“one mile per breath” (4 seconds) and says that such a motionmust have an effect on the things we see. Conclusion: The earth isat rest.

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Three sources III

Nas.ır al-Dın al-T. usı (Iran, Iraq, died 672/1274)Al-Tadhkira fı c ilm al-Hay’a / Memoir on the Science of CosmologyPhilosophical introduction on the structure of the cosmos(including the earth), 125 pages of text, no tables.Modifications of the Ptolemaic models of the universe.Arabic text with English translation [Ragep 1993].

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Models of the universe: Ptolemy

Sat

V

Jup

Sphere of Mars

Sphere of Jupiter

Sphere of Saturn

Sphere of the fixed starsOutermost sphere (signs of zodiac)

Sun

Mo

Me

E

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Islamic modifications in the solar motion

E

AApogee

S

Ptolemy: A fixed, in 5 Gemini,

Solar motion: E earth, S sun.

C center of orbit of sun.

CE:CA=1:243th/9th c. Islamic astronomers:

CE:CA approx. 1:30 (different values)

Al−Battani: A moves slowly

C

New values of the obliquity of the ecliptic: Ptolemy: 23o51′,corrected to 23o35′ in the 3d/9th century.

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Ptolemy’s equant model

M EqE

sun

Mars, Jupiter, Saturn acc. to Ptolemy

E=earth; center C of epicycle moveson circle with center M, motion is

Line C−P (Planet) is parallel to lineEarth − mean sun.

uniform with respect to Eq.

C

P

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Al-Tusi’s modification

EqE

sun

KL

C

P

Al−Tusi: K moves uniformlyaround Eq; KL and LC moveuniformly (so C has asinusoidal motion on EqK)

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Al-Tusi’s couple of circles

ω

ω

ω

2ωKL

C

EqAl−Tusi’s Principle ofSinusoidal Motion

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The universe of the Islamic theologians

The model of the universe used by Islamic astronomers differedfrom the model of the universe used by the Islamic theologians,especially after the 11th century.

Basis of the theological model: Koran, H. adıth (traditional reportsabout sayings of the Prophet Mohammad)”

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The universe of the theologians

The earth is flat, and that Heavens and Hells are layers above /below it.

Above the Earth, there are seven Heavens, below it, there areseven Hells.

God’s Throne is located above the seven Heavens.

To this model, traditional (folklore) elements are added (a fishsupporting the whole cosmos, etc.)

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Literature and exam problems

Literature: Steele, Ch. on Islamic astronomy, pp. 83-84, 99-133(you don’t have to memorize any Arabic names!)

Exam problem:1. see next presentation (about the theory of the sun)2. Describe the working of an astrolabe.

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Further literature (not for exam)

Anton Heinen, Islamic Cosmology. A study of as-Suyutis al-Hay’aas-sunniya fi l-hay’a as-sunniya with critical edition, translation andcommentary. Beiruter Texte und Studien no. 27, 1982.Nallino, Carlo Alfonso [Ed.]: Al-Battanı (d. 929) sive AlbateniiOpus Astronomicum. Ad fidem codicis escurialensis arabiceeditum. I-II. Latin translation and commentary. III. Arabic text.Rome, Milan 1899-1907. Reprinted Frankfurt 1997, IslamicMathematics and Astronomy. 11-13.Abu’l-Rayh. an al-Bırunı, al-Qanunu’l-Masc udı, An Encyclopaedia ofAstronomical Sciences, Hyderabad (India): Osmania OrientalPublications Bureau, 1954-1956, 3 vols.

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Further literature (not for exam)

Aby Raıchan Beryni (973-1048), Izbrannye Proizvedeniya, part 5,Kanun Mas‘yda, 2 vols. Translated by B.A. Rosenfeld and A.Akhmedov. Tashkent 1976.E.S. Kennedy, Al-Bırunı’s Masudic Canon, Al-Abhath 24, 1971,pp. 59-81, reprinted in E.S. Kennedy, Colleagues and Students,Studies in the Islamic Exact Sciences, Beirut 1983, pp. 573-595.F.J. Ragep, Nas. ır al-Dın al-T. usı’s Memoir on astronomyAl-Tadhkira fı c ilm al-Hay’a, New York: Springer 1993, 2 vols.

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Further literature (not for exam)

R. Ramsay Wright (trans.), The Book of Instruction in theElements of the Art of Astrology by al-Bırunı. London 1934. 699pp. Reprinted: Frankfurt 1998 (Islamic Mathematics andAstronomy. 29)E.S. Kennedy, A survey of Islamic Astronomical Tables,Philadelphia: American Philosophical Society, 1956.

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Further literature (not for exam)

D.A. King, J.Samso, B.Goldstein, Astronomical Handboks andTables from the Islamic world (750-1900): an Interim Report,Suhayl: Journal for the History of the Exact and Natural Sciencesin Islamic Civilization 2 2001, pp. 9-106.B.A. Rosenfeld, E. Ihsanoglu, Mathematicians, Astronomers andOther Scholars of Islamic civilization and their works (7th-19th c.),Iatanbul: IRCICA, 2003.

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Further literature (not for exam)

Fuat Sezgin, Geschichte des arabischen Schrifttums, Band 6,Astronomie bis ca. 430 H. Leiden: Brill, 1978.Aydin Sayılı, The Observatory in Islam and its PLace in the GeneralHistory of the Observatory, Ankara 1960, 427 pp. , reprintedFrankfurt 1998 (Islamic Mathematics and Astronomy vol. 97).