Ibn Yunus
Encyclopedia
Ibn Yunus (full name, Abu al-Hasan 'Ali ibn 'Abd al-Rahman ibn Ahmad ibn Yunus al-Sadafi al-Misri) (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.
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 traveler 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 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.
, noted for making predictions and having written the Kitab bulugh al-umniyya ("On the Attainment of Desire"), a work concerning the heliacal rising
s of Sirius
, and on predictions concerning what day of the week the Coptic
year will start on.
, 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".
Ibn Yunus described 40 planetary conjunctions and 30 lunar eclipse
s. For example, he accurately describes the planetary conjunction that occurred in the year 1000 as follows:
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 eclipse
s reliable enough to use them in his lunar theory to determine the secular acceleration of the moon
. Ibn Yunus also observed more than 10,000 entries for the sun
's position for many years using a large monument
al astrolabe with a diameter of nearly 1.4 metres.
though this is uncertain.
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 British historian Edward Bernard
.
Egyptians
Egyptians are nation an ethnic group made up of Mediterranean North Africans, the indigenous people of Egypt.Egyptian identity is closely tied to geography. The population of Egypt is concentrated in the lower Nile Valley, the small strip of cultivable land stretching from the First Cataract to...
Muslim astronomer
Islamic astronomy
Islamic astronomy or Arabic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age , and mostly written in the Arabic language. These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and...
and mathematician
Islamic mathematics
In the history of mathematics, mathematics in medieval Islam, often termed Islamic mathematics or Arabic mathematics, covers the body of mathematics preserved and developed under the Islamic civilization between circa 622 and 1600...
, whose works are noted for being ahead of their time, having been based on meticulous calculations and attention to detail.
The crater Ibn Yunus
Ibn Yunus (crater)
Ibn Yunus is the remains of a flooded lunar crater. It lies on the far side of the Moon, just past the eastern limb. It can only be viewed from Earth under conditions of favorable libration and lighting, and even then it is seen from the edge. This feature is attached to the east-southeastern outer...
on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
is named after him.
Life
Information regarding his early life and education is uncertain. He was born in EgyptEgypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
between 950 and 952 and came from a respected family in Fustat
Fostat
Fustat , was the first capital of Egypt under Arab rule...
. His father was a historian, biographer and scholar of hadith
Hadith
The term Hadīth is used to denote a saying or an act or tacit approval or criticism ascribed either validly or invalidly to the Islamic prophet Muhammad....
, who wrote two volumes about the history of Egypt—one about the Egyptians
Egyptians
Egyptians are nation an ethnic group made up of Mediterranean North Africans, the indigenous people of Egypt.Egyptian identity is closely tied to geography. The population of Egypt is concentrated in the lower Nile Valley, the small strip of cultivable land stretching from the First Cataract to...
and one based on traveler 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 al-Shafi.
Early in the life of Ibn Yunus, the Fatimid
Fatimid
The Fatimid Islamic Caliphate or al-Fāṭimiyyūn was a Berber Shia Muslim caliphate first centered in Tunisia and later in Egypt that ruled over varying areas of the Maghreb, Sudan, Sicily, the Levant, and Hijaz from 5 January 909 to 1171.The caliphate was ruled by the Fatimids, who established the...
dynasty
Dynasty
A dynasty is a sequence of rulers considered members of the same family. Historians traditionally consider many sovereign states' history within a framework of successive dynasties, e.g., China, Ancient Egypt and the Persian Empire...
came to power and the new city of Cairo
Cairo
Cairo , is the capital of Egypt and the largest city in the Arab world and Africa, and the 16th largest metropolitan area in the world. Nicknamed "The City of a Thousand Minarets" for its preponderance of Islamic architecture, Cairo has long been a centre of the region's political and cultural life...
was founded. In Cairo, he worked as an astronomer for the Fatimid dynasty for twenty-six years, first for the Caliph
Caliph
The Caliph is the head of state in a Caliphate, and the title for the ruler of the Islamic Ummah, an Islamic community ruled by the Shari'ah. It is a transcribed version of the Arabic word which means "successor" or "representative"...
al-Aziz and then for al-Hakim
Al-Hakim bi-Amr Allah
Abu ‘Ali Mansur Tāriqu l-Ḥākim, called Al-Hakim bi Amr al-Lāh , was the sixth Fatimid caliph and 16th Ismaili imam .- History :...
. Ibn Yunus dedicated his most famous astronomical work, al-Zij al-Kabir al-Hakimi, to the latter.
Astrology
In astrologyAstrology
Astrology consists of a number of belief systems which hold that there is a relationship between astronomical phenomena and events in the human world...
, noted for making predictions and having written the Kitab bulugh al-umniyya ("On the Attainment of Desire"), a work concerning the heliacal rising
Heliacal rising
The heliacal rising of a star occurs when it first becomes visible above the eastern horizon for a brief moment just before sunrise, after a period of time when it had not been visible....
s of Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...
, and on predictions concerning what day of the week the Coptic
Coptic calendar
The Coptic calendar, also called the Alexandrian calendar, is used by the Coptic Orthodox Church and still used in Egypt. This calendar is based on the ancient Egyptian calendar...
year will start on.
Astronomy
Ibn Yunus' most famous work in Islamic astronomyIslamic astronomy
Islamic astronomy or Arabic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age , and mostly written in the Arabic language. These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and...
, al-Zij
Zij
Zīj is the generic name applied to Islamic astronomical books that tabulate parameters used for astronomical calculations of the positions of the Sun, Moon, stars, and planets. The name is derived from the Middle Persian term zih or zīg, meaning cord...
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".
Ibn Yunus described 40 planetary conjunctions and 30 lunar eclipse
Lunar eclipse
A lunar eclipse occurs when the Moon passes behind the Earth so that the Earth blocks the Sun's rays from striking the Moon. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, a lunar eclipse can only occur the night of a...
s. 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. In the 19th century, Simon Newcomb
Simon Newcomb
Simon Newcomb was a Canadian-American astronomer and mathematician. Though he had little conventional schooling, he made important contributions to timekeeping as well as writing on economics and statistics and authoring a science fiction novel.-Early life:Simon Newcomb was born in the town of...
found Ibn Yunus' observations on conjunctions and eclipse
Eclipse
An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer...
s reliable enough to use them in his lunar theory to determine the secular acceleration of the moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. Ibn Yunus also observed more than 10,000 entries for the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
's position for many years using a large monument
Monument
A monument is a type of structure either explicitly created to commemorate a person or important event or which has become important to a social group as a part of their remembrance of historic times or cultural heritage, or simply as an example of historic architecture...
al astrolabe with a diameter of nearly 1.4 metres.
Poetry
Ibn Yunus is also thought to have been an Arabic poetArabic poetry
Arabic poetry is the earliest form of Arabic literature. Present knowledge of poetry in Arabic dates from the 6th century, but oral poetry is believed to predate that. Arabic poetry is categorized into two main types, rhymed, or measured, and prose, with the former greatly preceding the latter...
though this is uncertain.
Pendulum
Recent encyclopaedias and popular accounts continue to repeat the claim that the tenth century astronomer Ibn Yunus used a pendulumPendulum
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...
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 British historian Edward Bernard
Edward Bernard
Edward Bernard was an English scholar and Savilian professor of astronomy at the University of Oxford, from 1673 to 1691.-Life:He was born at Paulerspury, Northamptonshire. He was educated at Merchant Taylors' School and St John's College, Oxford, where he was a scholar in 1655; he became a Fellow...
.