Contributions of Ancient Arabian and Egyptian Scientists on Astronomy - Part 4

By: Md. Wasim Aktar
Deptt. of Agril. Chemicals, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal, India.

The astronomer and mathematician Wijan Ibn Rustam al-Kühi wrote many astronomical and mathematical works, including a treatise on the construction of the astrolabe. He was the head of the astronomers working in 988 at the Buwayhid Sharaf al-Dawlah’s observatory. (20) His co-worker Ahmad Ibn Muhammad al-Saghâni was the inventor and maker of astronomical instruments. Abu’l-Wafã is said to be the discoverer of the variation, the third inequality of the moon; a discovery which was later ascribed to Tycho Brahe. (21)

‘Ali Ibn al-Husain al-’Alawi (d. 985) showed a remarkable accuracy in observations. He compiled astronomical tables which remained very popular for at least two centuries. (22)

Now we come to a famous astronomer of the 10th century, named Abu’l-Husain ‘Abd al-Rahman al-Sufi. He was born in Ray (Persia) in 903, and died in 966. He was a prominent astronomer of the medieval times. His knowledge of both the Islamic and Greek astronomy, particularly uranometry, was comprehensive. He was the first to observe the change of the colour of stars, the change in the magnitude of stars, the proper motion of stars, the long period variable stars and the Southern constellations which have been wrongly ascribed by modern astronomers to some later ones.
Abd al-Rahman al-Sufi was patronized by the Buwayhid ruler Adud al-Dawlah (949—982) who was a great patron of astronomy, and had built an observatory at Shiraz. Al-Sufi wrote for the ruler a book on uranometry, entitled Suwar al-Kawàkib (The book of the fixed stars). In this book he gives a complete description of the constellations of the heavens. He also gives the position of each star of the constellations, illustrating with pictures. The book contains 55 astronomical tables along with illustrations of 48 constellations in 96 diagrams as seen in the heavens. The artistic value of the pictorial illustrations in the Mss. of this work is very great, and represents one of the best examples of the Persian miniature paintings. Al-Sufi has not only corrected the errors of observations in the work of his predecessors like al-Battãni, but also, pointed out many faulty observations found in Ptolemy’s Almagest. He defined carefully the boundaries of each constellation, and recorded the magnitudes and positions of stars after making new observations.

The Suwar al-Kawàkib is one of the three masterpieces of observational astronomy of the medieval times; the other two being the catalogues of Ibn Yünus and Ulugh Beg prepared in the 12th and 15th centuries respectively. It is an addition to the Muslims’ knowledge on uranometry. The later astronomers, like al-Biruni, Alfonso, Prince of Castile, Khwãjah Näsir al-Din Tusi, Prince Ulugh Beg and Jai Singh II, based their catalogues of stars on this authentic catalogue. This work was translated into Latin, French and Persian, and a commentary on it was written in Spanish.
It served as a basis for later works in Western Europe. The modern astronomers like Hauber, Down, Argelander, Ideler, Schellerup and Knobel had made an extensive use of it.

Al-Sufi prepared a fine celestial globe. Several celestial globes which cover the period from the 11th to the 18th century show the star positions and magnitudes according to al-Sufi. He showed a remarkable accuracy in the design of the astrolabes. He wrote a treatise on this instrument. In this treatise he throws light on the astronomical techniques as practiced it that time. (23)

Another great astronomer and one of the greatest Muslim astronomers was Abu’l-Hasan Ali Ibn Abi Said ‘Abd al-Rahman Ibn Ahmad Ibn Yünus al-Sadafi, generally known as Ibn Yünus. He was well versed in Arabic literature, poetry and history, and had knowledge of many other subjects. He belonged to Egypt where he died in 1009. He was a courtier of the Fatimi Caliph al-‘Aziz Billah (975—996). He got a chance of working in a well-equipped observatory which was the part of a Muslim academy of science, named Dar al-Hikmah (the house of wisdom) founded in Cairo by the Fatimi rulers. He made astronomical observations, and by the order of the Caliph al-‘Aziz he compiled the astronomical tables. The work of compilation of these tables was begun in 990 during the lifetime of the Caliph, but it was completed after his death under his son al- Hakim (966—1020). Hence they were named after him Al-Zij al-Kabir al-Hakimi. In these tables he entered his observations about the eclipses and conjunctions, old and new, improved values of astronomical constants (inclination of the ecliptic, 23° 35’; longitude of the sun’s apogee, 86° 10’; solar parallax reduced from 3’ to 2’; precession, 51.2” a year). He gave an account of the geodetic measurements which were carried on by the order of the Caliph al-Ma’mun in the ninth century.
Ibn Yünus in his astronomical tables (written in 4 volumes) corrected the errors of observations in the astronomical tables of his predecessors. The people of Egypt relied on these tables. It is said that after their compilation the use of all the previous tables in the world was given up. Even the astronomers of China greatly utilized them. The translation of a large part of the tables, except the chronological section, has been made in French in 1804.

Beside these-tables, Ibn Yünus has composed many books. One of these is Jadawil al-Samt (the tables of direction), and the other is the Jadawil al-Shams wa’l-Qamar (the tables of the sun and the moon). (24)