Ibn Yunus

Ibn Yunus
Born	Abu al-Hasan 'Ali Abi al-Said ibn 'Abd al-Rahman ibn Ahmad ibn Yunus bin Abd al-'Ala al-Sadafi al-Misri (أبو الحسن علي أبي السعيد بن عبد الرحمن بن أحمد بن يونس بن عبد الأعلى الصدفي المصري) 950 Fustat,Ikhshidid Emirate of Egypt,nowEgypt
Died	6 June 1009 Cairo,Egyptian Fatimid Caliphate,nowEgypt
Occupation(s)	Astronomer,astrologer,mathematician,philosopher
Era	Ikhshidid era Abbasid era Fatimid era
Notable work	Al-Zij al-Kabir al-Hakimi Bulugh al-Umniyya Zij ibn Yunus Ghayat al-Intifah fi Mareafat al-Da'ir min al-Falak min qabl al-Iritifah

Abu al-Hasan 'Ali ibn Abi al-Said 'Abd al-Rahman ibn Ahmad ibn Yunus ibn Abd al-'Ala al-Sadafi al-Misri(Egyptian Arabic:ابن يونس; c. 950 – 1009) was an importantEgyptianastronomer andmathematician,whose works are noted for being ahead of their time, having been based on meticulous calculations and attention to detail. He is one of the famousMuslimastronomers who appeared afterAl-BattaniandAbu al-Wafa' al-Buzjani,and he was perhaps the greatest astronomer of his time. Because of his brilliance, theFatimidsgave him generous gifts and established an observatory for him on Mount Mokattam nearFustat.Al-Aziz Billahordered him to make astronomical tables, which he completed during the reign ofAl-Hakim bi-Amr Allah,son of Al-Aziz, and called it al-Zij al-Kabir al-Hakimi. The craterIbn Yunuson theMoonis named after him.

Ibn Yunus' records of the solar eclipses of 993 and 1004 as well as the lunar eclipses of 1001 and 1002.

Life

Information regarding his early life and education is uncertain. He was born inEgyptbetween 950 and 952 and came from a respected family inFustat.His father was a historian, biographer, and scholar ofhadithwho wrote two volumes about the history of Egypt—one about theEgyptiansand one based on traveller commentary on Egypt.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".His grandfather was also one of the scholars who specialized in astronomy, and Ibn Yunus enjoyed great prestige among the Fatimid caliphs, who encouraged him to pursue his astronomical and mathematical research. They built an observatory for him near Fustat (Cairo), and equipped it with all the necessary machinery and tools.Sartonsays of him that he was perhaps the greatest Muslim astronomer. His great-grandfather had been an associate of the noted legal scholaral-Shafi'i.

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

As well as for his mathematics, Ibn Yunus was also known as an eccentric and a poet.

Works

One of his greatest astronomical works was that he calculated with great accuracy the inclination of the ecliptic circle, after observing the solar and lunar eclipses.

Ibn Yunus excelled in trigonometry, and he was the first to solve some of the trigonometric equations that are used in astronomy, and he conducted valuable research in it that helped advance trigonometry. He was the first to establish a law for spherical trigonometry, and it was of great importance to scholars of astronomy, before the discovery of logarithms, since by means of that law multiplication operations in trigonometry could be converted into addition operations, it facilitated the solution of many long and complex problems.

Ibn Yunus showed great ingenuity in solving many difficult problems in astronomy.

Ibn Yunus observed the eclipse of the sun and moon in Cairo in 978 AD, and his calculation came closest to what was known, until modern observing machines appeared.

Astrology

Inastrology,noted for making predictions and having written theKitab bulugh al-umniyya( "On the Attainment of Desire" ), a work concerning theheliacal risingsofSirius,and on predictions concerning what day of the week theCopticyear will start on.

Astronomy

Ibn Yunus lunar crater, named after him

Ibn Yunus' most famous work inIslamic astronomy,al-Zijal-Kabir al-Hakimi(c. 1000), 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, theZij al-Kabir al-Hakimiis "a work of outstanding originality of which just over half survives".

Yunus expressed the solutions in hiszijwithout mathematical symbols,butDelambrenoted in his 1819 translation of the Hakemite tables that two of Ibn Yunus' methods for determining the time from solar or stellar altitude were equivalent to thetrigonometric identity$2\cos(a)\cos(b)=\cos(a+b)+\cos(a-b)$identified inJohannes Werner's 16th-century manuscript on conic sections. Now recognized as one of Werner's formulas, it was essential for the development ofprosthaphaeresisandlogarithmsdecades later.

Ibn Yunus described 40planetary conjunctionsand 30lunar eclipses.For example, he accurately describes the planetary conjunction that occurred in the year 1000 as follows:

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. Ibn Yunus's observations on conjunctions andeclipseswere used inRichard DunthorneandSimon Newcombs' respective calculations of the secular acceleration of theMoon.

Pendulum

Recent encyclopaediasand popular accountsclaim that the tenth century astronomer Ibn Yunus used apendulumfor time measurement, despite the fact that it has been known for nearly a hundred years that this is based on nothing more than an error made in 1684 by the Savilian Professor of Astronomy at OxfordEdward Bernard.

Ibn Yunus's philosophy

The book “Ghayat al-Intifah fi Mareafat al-Da'ir min al-Falak min qabl al-Iritifah”by the scholar Abu Al-Hasan Ali Ibn Yunus

In his scientific studies, he only believed in what his mind was convinced of, and he did not care what people said about him. His philosophy was summarized in three points:

• Adopting the scientific principle based on observation and measurement, and taking the universe and everything in it as a teacher, from which facts are deduced and to which they are returned.
• Strengthening faith by touching the signs of the Creator emanating in the universe.
• Practicing legitimate pleasures. (Ibn Khallikanmentions about one of the astrologers that he once went with him to Mount Mokattam, and he stopped to observe the planet Venus, so he took off his turban and dress and put on a red shirt and a red mask to cover himself with. He took out a stick and struck it with incense in his hands, and his situation was bizarre).

Narration of Hadith

Ibn Yunus narrated hadiths and reports from his father, Abi al-Sa'id, but the scholars rejected his narration due to his preoccupation with astrology and magic.

Books

Ibn Yunus had many works, and his most important book isAl-Zij Al-Kabir Al-Hakimi,which is the book he began writing, by order of the Fatimid Caliph Al-Aziz in the year 380 AH/990 AD, and completed it in 1007 AD during the reign of Caliph Al-Hakim Ould Al-Aziz, and he called it Al-Zij Al-Hakimi, after the caliph.

The wordZijis a Persian word (Zik), and its meaning in our modern sense is mathematical astronomical tables. He had another book calledZij Ibn Yunus,and the numbers he included in his twozijbooks are correct up to the seventh decimal number, which indicates unparalleled mathematical accuracy in calculations, and many astronomers have been transmitted from him, especially after hiszijmoved to the East, and the Egyptians relied on their calendars on Ibn Yunus’zijfor a long period of time.

External links

• King, David A. (2007)."Ibn Yūnus: Abū al-Ḥasan ҁʿAlī ibn ʿAbd al-Raḥmān ibn Aḥmad ibn Yūnus al-Ṣadafī".In Thomas Hockey; et al. (eds.).The Biographical Encyclopedia of Astronomers.New York: Springer. pp. 573–4.ISBN978-0-387-31022-0.(PDF version)
• O'Connor, John J.;Robertson, Edmund F.,"Abu'l-Hasan Ali ibn Abd al-Rahman ibn Yunus",MacTutor History of Mathematics Archive,University of St Andrews
• King, David A. (2008) [1970-80]."Ibn Yūnus, AbuʿL-Hasan ʿAlī Ibn ʿ Abd Al-Rahmān Ibn Yūnus Al Sadafī".Complete Dictionary of Scientific Biography.Encyclopedia.
• Ibn Yunus Biography