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Ibn Yunus

Ibn Yunus (Arabic: ابن يونس) (full name, Abu al-Hasan 'Ali abi Sa'id 'Abd al-Rahman ibn Ahmad ibn Yunus al-Sadafi al-Misri) (c. 950-1009) was an important Egyptian Muslim astronomer and mathematician,[1][2][3][4] whose works are noted for being ahead of their time, having been based on almost modern-like meticulous calculations and attention to detail.

The crater Ibn Yunus on the Moon is named after him.



Information regarding his early life and education is uncertain. He was born in Egypt between 950 and 952 AD and came from a respected family in Fustat. His father was a historian, biographer and scholar of hadith, who wrote two volumes about the history of Egypt—one about the Egyptians and one based on traveler commentary on Egypt.[5] A prolific writer, Ibn Yunus' father has been described as "Egypt's most celebrated early historian and first known compiler of a biographical dictionary devoted exclusively to Egyptians".[6] His great grandfather had been an associate of the noted legal scholar al-Shafi.

Early in the life of Ibn Yunus, the Fatimid dynasty came to power and the new city of Cairo was founded. In Cairo, he worked as an astronomer for the Fatimid dynasty for twenty-six years, first for the Caliph al-Aziz and then for al-Hakim. Ibn Yunus dedicated his most famous astronomical work, al-Zij al-Kabir al-Hakimi, to the latter.



In astrology, noted for making predictions and having written the Kitab bulugh al-umniyya ("On the Attainment of Desire"), a work concerning the heliacal risings of Sirius, and on predictions concerning what day of the week the Coptic year will start on.


Ibn Yunus' most famous work in Islamic astronomy, al-Zij al-Kabir al-Hakimi (c. 1000 AD), was a handbook of astronomical tables which contained very accurate observations, many of which may have been obtained with very large astronomical instruments. According to N. M. Swerdlow, the Zij al-Kabir al-Hakimi is "a work of outstanding originality of which just over half survives".[7]

Ibn Yunus described 40 planetary conjunctions and 30 lunar eclipses. For example, he accurately describes the planetary conjunction that occurred in the year 1000 AD as follows:[8]

"A conjunction of Venus and Mercury in Gemini, observed in the western sky: The two planets were in conjunction after sunset on the night [of Sunday 19 May 1000]. The time was approximately eight equinoctial hours after midday on Sunday ... . Mercury was north of Venus and their latitude difference was a third of a degree."

Modern knowledge of the positions of the planets confirms that his description and his calculation of the distance being one third of a degree is exactly correct. In the 19th century, Simon Newcomb found Ibn Yunus' observations on conjunctions and eclipses reliable enough to use them in his lunar theory to determine the secular acceleration of the moon.[8][9] Ibn Yunus' other observations also inspired Laplace's Obliquity of the Ecliptic and Inequalities of Jupiter and Saturn's.[clarification needed (incomplete title)] Ibn Yunus also observed more than 10,000 entries for the sun's position for many years using a large monumental astrolabe with a diameter of nearly 1.4 metres.[9]


Ibn Yunus is also thought to have been an Arabic poet, and to have used very large instruments in making his observations, though neither assertion is certain.

Other works

Many sources claim Ibn Yunis used a pendulum for time measurement[10][11][12][13][14], but other sources claim this was a myth started in 1684 by British historian Edward Bernard.[15][16]

He is said to have predicted his own death, seven days prior to the event, and without any outward sign of ill health.


  1. ^ Ivan van Sertima, Egypt: Child of Africa, p. 337.
  2. ^ Science & Technology in the Islamic World - Page 77
  3. ^ Science in Medieval Islam: an illustrated introduction by Howard R. Turner - Page 65
  4. ^ Eternal Egypt. Ibn-Yunus El-Falaky.
  5. ^ Eternal Egypt. Ibn Yunus The Historian.
  6. ^ Eickelman, Dale F. James Piscatori. Muslim Travellers: Pilgrimage, Migration, and the Religious Imagination. Berkeley: University of California Press, 1990. p. 58
  7. ^ N. M. Swerdlow (1993), "Montucla's Legacy: The History of the Exact Sciences", Journal of the History of Ideas 54 (2): 299-328 [320].
  8. ^ a b O'Connor, John J.; Robertson, Edmund F., "Abu'l-Hasan Ali ibn Abd al-Rahman ibn Yunus", MacTutor History of Mathematics archive .
  9. ^ a b Salah Zaimeche (2002), The Muslim Pioneers of Astronomy, FSTC
  10. ^ Good, Gregory (1998). Sciences of the Earth: An Encyclopedia of Events, People, and Phenomena. Routledge. pp. 394. ISBN 081530062X,. 
  11. ^ Newton, Roger G. (2004). Galileo's Pendulum: Rhythm of Time to the Making of Matter. US: Harvard University Press. pp. 52. ISBN 067401331X. 
  12. ^ Briffault, Robert (1928). The Making of Humanity. London: George Allen & Unwin. pp. 191. ISBN B00088VH2O. 
  13. ^ "Pendulum". Encyclopedia Americana. 21. The Americana Corp.. 1967. pp. 502. Retrieved 2009-02-20. 
  14. ^ Baker, Cyril Clarence Thomas (1961). Dictionary of Mathematics. G. Newnes. pp. 176. 
  15. ^ O'Connor, J. J.; Robertson, E. F. (November 1999). "Abu'l-Hasan Ali ibn Abd al-Rahman ibn Yunus". University of St Andrews. Retrieved 2007-05-29. 
  16. ^ King, D. A. (1979). "Ibn Yunus and the pendulum: a history of errors". Archives Internationales d'Histoire des Sciences 29 (104): 35–52. 

He is said to have predicted his own death, seven days prior to the event, and without any outward sign of ill health.

Ibn Yunus is believed to have described an early type of pendulum in the 10th century. Some claimed that he used it for making measurements of time, but this is now believed to be a misinterpretation on the part of Edward Bernard, an English historian.[7][8]

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