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) (c. 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.

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

[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] Works

[edit] Astrology

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.

[edit] Astronomy

In astronomy, 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 observed horizon is one of the oldest recorded values for this quantity. 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.

In the nineteenth century, Simon Newcomb found his observations on eclipses reliable enough to use them in determining the secular acceleration of the moon. His other observations also inspired Laplace's Obliquity of the Ecliptic and Inequalities of Jupiter and Saturn's. He also observed more than 10,000 entries for the sun's position for many years using a large astrolabe with a diameter of nearly 1.4 metres.^[7]

[edit] Mathematics

In mathematics, he demonstrated the trigonometric identity

[edit] Poetry

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.

[edit] Other works

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.^[8][9]

[edit] References

[edit] External links

• O'Connor, John J. & Robertson, Edmund F., “Abu'l-Hasan Ali ibn Abd al-Rahman ibn Yunus”, MacTutor History of Mathematics archive 
• Ibn Yunus Biography