Islamic Civilization

Greek Vs Islamic Astronomy

 The assertion that Islamic astronomy is a mere reproduction of Greek astronomy is groundless as this chapter will abundantly show. Briefly are considered  here some fundamental differences between Islamic and Greek astronomy.

First, Muslim astronomers dealt with a considerable number of subjects Ptolemy never addressed or contemplated, or could even address or contemplate, all subjects, which are today the realm of modern astronomy.  The briefest set of instances will show that it is not in Ptolemy that one finds trigonometrical calculations relating to this subject,[1] nor the many calculations, findings, and theories that the hundreds of Muslim astronomers made,[2] nor the use of observation for scientific purposes.[3] Ptolemy’s tables did not stand in comparison with Muslim tables, such as al-Zarqali’s for instance.[4] It was also the Muslims who initiated the greatest breakthroughs in the issue of planetary theories, and not Ptolemy or other Greek astronomers.[5] Moreover, contrary to Ptolemy, Muslim astronomers such as al-Sijzi (fl late 9^th century) did conceive that the earth was moving in its own axis.[6] This is further confirmed by another astronomer of the 13^th century, Al-Harrani, who held ‘according to the geometers (or engineers) (muhandeseens), the earth is in constant circular motion, and what appears to be the motion of the heavens is actually due to the motion of the earth and not the stars.’[7] Muslim astronomers, besides exploring issues never addressed by Ptolemy, refuted him, and even ridiculed him.[8] This will be made particularly obvious in the section dealing with Andalusian astronomers.

The second most important difference between Islamic and Greek astronomy is that, unlike its Greek predecessor, Islamic astronomy was not just the work of a handful of figures, in fact, mainly a lone figure (Ptolemy), but literally that of hundreds. Suter, early in the 20^th century, listed over 500 Muslim astronomers,[9] a figure since augmented considerably by Sarton[10] and Sezgin.[11] A recently published work by Rosenfeld and Ihsanoglu has made an up-date of the works and accomplishments of hundreds of Muslim astronomers whose scope was far reaching, and had considerable influence on modern astronomy.[12]

Thirdly, Islamic astronomy was universal in its character, and as to be seen below under Observation , it generally involved teams of workers in specified tasks. Illustrating this universal-team work character is the fact that often, even members of the same family collaborated. The three Banu Musa bothers, for instance, made observations and worked on diverse scientific subjects in a collaborative effort.[13] The same with Ibn Amajur, the father, who made observations between 885 and 933, with his son Abu-l Hasan Ali and an emancipated slave named Muflih.[14] They were some of the greatest observers of Islam, father and son, and Muflih, making many observations, and producing numerous astronomical tables.[15] There is also the mention of another member of the family, and collaborators working with them.[16]

Fourthly, and more importantly, very early, Muslims astronomers, like other Muslim scientists, insisted on the need not just for observation and calculation, but also repeated verifications of results. Briffault notes how Muslims compiled new sets of planetary tables, and obtained more accurate values for the obliquity of the ecliptic and procession of equinoxes, that were checked by two independent measurements of a meridian the estimates of the size of the earth.[17] Al-Biruni  and Abu’l Wafa (940-998), for instance, made in the year 997 arrangements to observe the lunar eclipse of that year and compare notes; Abu’l Wafa observing it in Baghdad  while al-Biruni made the observation in Khwarizm.[18] The search for accuracy was such that on the inaugural observations made at the 10^th century Sharaf al-Dawla Observatory  of Baghdad, for instance, official documents were drawn up testifying to the accuracy of the instruments and the observations, and jurists were among the signatories of these documents.[19] To reach ever more precise results, Muslim astronomers devised more precise and larger instruments, which is the fifth main difference with Greek astronomy.

Fifthly, instruments built by Muslim astronomers surpass anything Greek astronomy did.[20] Muslim astronomers, for instance, defined their findings, and devised their astronomical tables through observations and calculations, and using for the first time sophisticated apparatus for such operations.[21] Al-Battani  recommends for parallax measurements the use of the large, or huge, quadrant and the parallactic ruler.[22]

The following highlights further the points just made, and dwells on the various Muslim accomplishments in the field.