Abu al-Hasan 'Ali ibn 'Abd al-Rahman ibn Ahmad ibn Yunus al-Sadafi al-Misri (Arabic: ابن يونس; c. 950 – 1009) was an
important Egyptian Muslim astronomer and mathematician, whose
works are noted for being ahead of their time, having been based on meticulous
calculations and attention to detail.
The crater Ibn
Yunus on the Moon is named after him.
Life
Information regarding
his early life and education is uncertain. He was born in Egypt between 950 and
952 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 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 great-grandfather had
been an associate of the noted legal scholar Imam 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.
As well as for his mathematics, Ibn Yunus was also known as an eccentric
and a poet.
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.
Astronomy
Ibn Yunus' most famous
work in Islamic astronomy, al-Zij al-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, the Zij al-Kabir al-Hakimi is
"a work of outstanding originality of which just over half survives".
Yunus expressed the
solutions in his zij without mathematical
symbols, but Delambre noted 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 the trigonometric identity identified
in Johannes Werner's 16th-century manuscript on conic sections. Now
recognized as one of Werner's formulas, it was essential for the development
of prosthaphaeresis and logarithms decades later.
Ibn Yunus described
40 planetary conjunctions and 30 lunar 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 and eclipses were used in Richard
Dunthorne and Simon Newcombs' respective calculations of the secular
acceleration of the moon.
Pendulum
Recent encyclopaedias and popular accounts claim that the tenth
century astronomer Ibn Yunus used a pendulum for 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 Oxford Edward Bernard.
Sumber
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