Ibn Yunus

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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) (950?-1009) was an important Egyptian mathematician and astronomer^[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.

He demonstrated the trigonometric identity

$\cos(a) \cos(b) = 1/2 [\cos(a+b) + \cos(a-b)]\!$

1 Life
2 Work
3 References
4 External links

[edit] Life

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-Hakimi al-kabir, to the latter. This handbook of astronomical tables contained very accurate observations, many of which may have been obtained with very large astronomical instruments.

[edit] Work

One remarkable aspect of his turn of the millennium calculations is that he took atmospheric refraction of the Sun's rays at the horizon into account in his observations. His figure of forty minutes of arc between the "true" horizon and the observed horizon is one of the oldest recorded values for this quantity. In the nineteenth century, Simon Newcomb found his observations reliable enough to use them in determining the secular acceleration of the moon.

Ibn Yunus is also thought to have been a poet, and to have used very large instruments in making his observations, though neither assertion is certain. Two of the instruments said to have been used by him include an armillary sphere having nine rings, each of which was said to have weighed 2,000 pounds, and large enough for a horse and rider to pass through; and a copper astrolabe three cubits across.

He was also an astrologer, 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.

It is alleged that he predicted his own death, seven days prior to the event, and without any outward sign of ill health. He also invented the pendulum.

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

[edit] References

^ Egypt: Child of Africa by Ivan Van Sertima - Page 337
^ Science & Technology in the Islamic World - Page 77
^ Science in Medieval Islam: an illustrated introduction by Howard R. Turner - Page 65
^ Eternal Egypt. Ibn-Yunus El-Falaky.
^ Eternal Egypt. Ibn Yunus The Historian.
^ Eickelman, Dale F. James Piscatori. Muslim Travellers: Pilgrimage, Migration, and the Religious Imagination. Berkeley: University of California Press, 1990. p. 58