Contributions of Ancient Arabian and Egyptian Scientists on Astronomy - Part 2

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

The Muslim astronomers also prepared the star maps to preserve the old astronomical knowledge, and to use them as an aid to travel, navigation and meteorology.

A great incentive for the study of astronomy came from an Indian astronomical work called Siddhanta which was brought to the court of Baghdad by a Hindu named Kanka. Kanka met Ya’qüb Ibn Tãriq in 767 who was one of the greatest astronomers of his time. Ya’qüb Ibn Tãriq introduced him to the Caliph Al-Mansür.(3) Kanka showed the book to the Caliph who ordered Muhammad Ibn Ibrahim Al-Fazãri to translate it into Arabic.(4) He also ordered that a work based on Siddhanta should be composed, which could serve as a reference book for the Arabs. Muhammad Ibn Ibrahim took this responsibility and prepared a book which was called by the astronomers as Sind Hind al-Kabir (the great Siddhanta). (5) It was used until the time of the Caliph Al-Ma’mun. Then Al-Khwãrizmi, who was one of the greatest scientists, prepared a summary of this book. He also compiled astronomical and trigonometrical tables according to the combined methods of Indians, Persians and Greeks. These tables were revised by Maslamah al-Majriti (c. the second half of the 10th century). They gained so much popularity that they were used even in China. In the 12th century, the translation of these tables was made into Latin. (5) Al-Khawarizmi glimpsed in his works on astral motion and the force of attraction the law of universal gravitation.

The astronomer Ibrahim Ibn Habib al-Fazãri was the first Muslim who constructed astrolabes. He composed a poem on astrology, and compiled a Zij (calendar) according to the Arab method. He also wrote on the use of astrolabes and on the armillary spheres. (6)

In 762-63 the Persian astronomer and engineer, Naubakht, together with Masha’ Allah (Latin Macellama, Macelarama, Messahala), made a survey before the building of Baghdad. Masha’ Allah (d. 815 or 820) was one of the earliest astronomers and astrologers, who flourished under the Caliph Al-Mansür. (7) Naubakht (d. 776-77) was the author of a book on astrological judgments entitled Kitäb al-Ahkam. (8)

During the reign of the Caliph al-Ma’mun, the important work of translation of Ptolemy’s Almagest from Greek into Arabic was completed. The Caliph was very anxious to get it translated correctly. It was translated several timed. Many commentaries on it were written. Its summaries were also made. The Minister Yahya Ibn Khalid Barmaki was the first to get it translated. A group of scholars wrote for him a commentary on this book, but he did not like it. He appointed Abu Hasan and Salman who were attached to the scientific academy called Bait al-Hikmah (The house of wisdom) to write a commentary on it.(9) The Almagest represents the best example of Greek classical works on astronomy. It served as a basis for the later astronomical works. Al-Hajjaj Ibn-Yusuf was one of the first translators of the Almagest. He made this translation on the basis of a Syriac version. (10)

The Caliph al-Ma’mun (169-218 / 786-833) was very fond of philosophy and science. The more he got acquainted with the interesting problems of science, the more his interest grew in the practical work. He built an observatory at Baghdad in his Bait al-Hikmah and another in the plain of Tadmor (Palmyra). In these observatories the fundamental elements of the Almagest like the inclination of the ecliptic, the length of the solar year, and the precession of the equinoxes were verified. Observations on the celestial motions were carried out and geodetic measurements were made. (11)
Al-Ma’mun ordered Ahmed, Muhammad and Hasan, who were eminent scientists and his courtiers, to measure in collaboration with other court scientists the length of the terrestrial degree and the circumference’ of the earth in some vast planes. The planes of Sinjar and Tadmor were selected for this purpose. The astronomers stayed at a place and noted with the help of instruments the altitude of the North. Pole, and pitched a nail there. Then tying a long rope with the nail, they carried the rope in the direction of the North. Where the rope ended they pitched another nail and tied another rope with it, and proceeded in the same direction. They continued this process as well as observations on the altitude of the North Pole, until on reaching a particular spot they noticed that the altitude of this Pole had increased by one degree. The distance they covered was also measured, which was found to be 56 2/3 miles. From, these observations it was inferred that for each terrestrial degree the distance covered on the earth amounts to 56 2/3 miles. The same operation was repeated in the direction of the South where at one spot they noticed that the altitude had decreased by, one degree. The distance covered was the same as in the first case. Now on multiplying this distance by 360 which is the total number of terrestrial degrees, the circumference of the earth was found to be equal to 20,400 miles, and the diameter equal to 6,500 miles. (12)

The chief of astronomers who carried observations under al-Ma’mun was Sanad Ibn ‘Ali. He was a Jewish convert to Islam. He constructed an observatory (Kanisah) at the back of the Shamãsiah Gate at the palace of Mu’izz al-Dawlah in Baghdad. An astronomical table and some writings on astronomy and mathematics, including a book on Arabic numerals, are ascribed to him. (13)