Arabic Culture and Islamic Astronomy

The decay and destruction of the Roman empire carried with it much of the classical inheritance from Greece. Although part of the heritage was preserved by the monasteries and Byzantium, the majority of the works of antiquity were lost. Some of the Greek material was translated into

Arabic in the first millennium (e.g., the al Magest) and was later rediscovered by Europe.

An example is seen in the writing of Abu Ma'shar [astrologer, d. 886] (Pingree 1968), who used a Persian translation of 542 of the Sphaera Barbarica of Teukros [Babylonian? Lived between 100 b.c. and 50 a.d.] (Boll 1909, cited in Neugebauer 1957/1969, pp. 171, 189). This astrological work also contains material from India (see §§7.5 and 9.1.3). Islamic astronomy flourished under the 9th-century Abbasid Khalifate in Baghdad, and in addition to Abu Ma'shar, the astronomers Thabit ibn Qorra [from Harran on the Euphrates; 836?-901] (see Morelon 1987) and al-Khwarizmi lived during this time. Al-Khwarizmi developed astronomical tables that again demonstrate both Hindu and Greek influences. The Jewish astronomer Sind ben Ali [fl. ~830] was a principal contributor to tables drawn up under Sultan Maimun, and other Jewish scholars were involved in drawing up the Toledo Tables, ~1080.

Al-Battani or, as Europe knew him, Albategnius [Moslem astronomer, also from Harran, fl. 851-929], was one of the greatest of the Arab astronomers. He wrote commentaries on the astrological work of Ptolemy, Tetrabiblos, and wrote astronomical treatises and tables of lunar and solar motion. He found improved values of the obliquity of the ecliptic and the length of the tropical year, found a value for the precession of the equinoxes, 55 arc-secs/year, better than any since the time of Hipparchos, and rejected the theory of trepidation (§§7.3.3, 7.7). He used measurements of the lengths of the seasons (93d 14h of spring; 93d 00h for summer) to derive the properties of the solar eccentric and in essence discovered the apsidal motion of the Sun's orbit by noting a difference between his value for the longitude of the apogee (82°17') and Ptolemy's (65°30'). Al-Battani was a gifted observer who accurately recorded the circumstances of lunar and solar eclipses and developed a theory to determine the first visibility of the new (i.e., waxing crescent) moon. Finally, he also developed solutions to spherical trigonometry problems by the use of orthographic projections. His observations and books were translated and used for several centuries in Europe, as we note below.

Ibn Yunus [Arab astronomer, d. 1009] developed the Hakemite Tables and quoted Persian observations of the solar apogee from ~470 and 630 a.d. Works of Teukros and the Ptolemy contemporary Vettius Valens appeared in a Middle-Persian translation (Nallino, cited in Neugebauer 1959/1969).

Al-Blruni [fl. ~1030] (see Sachau 1910) played a direct, although late, role in the cultural transmission process. He wrote

I am . . . composing for the Hindus a translation of the books of Euclid and of the Almagest, and dictating to them a treatise on the construction of the astrolabe, being simply guided herein by the desire of spreading science.

He also translated Indian astrological works into Arabic.

Islamic astronomers also criticized Ptolemy. Alhazen [Ibn al-Haytham, 965—1040] attacked Ptolemy's model for the Moon and, more generally, the equant as an unsatisfactory mechanism for preserving uniform circular motion. Averroes [Ibn Rushd, Cordoba, 1126-1198] also criticized the equant, as well as other aspects of Ptolemaic theory. Nasir ad-Din at-Tusl [Khurasan, d. 1274] of the Maragha Obser-vatory46 similarly attacked the equant, but for the first time proposed an alternative. His replacement mechanism, known today as the Tusi couple (Kennedy 1966), consisted of two additional small-amplitude epicycles. This device was later to find its way into Copernicus's procedures (cf. §7.7) Alternative mechanisms were furnished by other astronomers at the Maragha Observatory, Mu'ayyad ad-Din al-'Urdi and Qutb ad-Din ash-Shlrazi. Finally, Ibn ash-Shatir [Damascus, ~1350] reworked Ptolemy's models for Mercury and the Moon with the help of the 'Tusi couple. This work enabled the deferent orbits to be fully concentric, thus, permitting the return of the concentric spheres. Although marking a great achievement, the legacy of this work was ultimately limited; Ibn ash-Shatir's success in transforming Ptolemaic mechanisms of Mercury and the Moon to the outer parts of the model, and thereby making possible a renesting of the celestial spheres, was generally unknown in the Middle Ages, and rediscovered only in the 1950s (Gingerich 1993, p. 141).47 One astronomer whose work was influential in Europe, Al-Bitruji (late 12th-13th century) also favored the system of concentric spheres. His work on the homocentric system is said to have caused great controversy in Europe when it was translated into Latin.

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