Science in Western Islam: Astronomy

by Monica Rius Pinies Published on: 22nd December 2022

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The history of science is a fundamental element in constructing a full understanding of the history of society. Furthermore, we must keep in mind that the globalization of ideas has occurred since ancient times, such that an appreciation of who we are is impossible without a proper analysis of all the input we have received thus far. Therefore, it is crucial that we stop and reflect upon the advancement of science in Western Islam, as it will provide us with a broader and clearer vision of our own culture. Particularly, it will demonstrate that we, too, are heirs of the Arabic [Muslim Civilisation] cultural legacy.

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Since thousands of years ago, the Mediterranean Sea has been a melting pot for the circulation of ideas and, indeed, of people. However, during the Middle Ages, the most notable of these movements was surely that between the Islamic East (Mashriq) and West (Maghreb). In expeditions taken to study abroad, Muslim scientists became especially active participants in the diffusion of knowledge as well as the advances that were being amassed in the capital of the empire, Baghdad. Moreover, these journeys were intimately linked to religious precepts. Far from being mere “carriers” of science, the cultural achievements of Muslim scientists during the Abbasid Golden Age would mark them as members of history’s intellectual elite. Although initially discretely out of the limelight, the scientists of North Africa and especially those of Al-Andalus played an essential role in the transmission of Eastern science to Europe, where the torch would be taken up. For this reason, it is impossible to understand the further development of science without recognizing the stepping-stone that was the Arabic-Islamic contribution. Diverse disciplines were cultivated, including medicine, agronomy, and optics, but undoubtedly the reigning field was astronomy (related, in turn, to mathematics and geography). The most relevant names in astronomy (from al-Khwarizmi to Ibn al-Zarqalluh) and the milestones their bearers achieved should be reason enough to have guaranteed their lasting fame. And yet, they remain largely unheard of…

Fig. 1. One of the craters on the moon located in section 33 is named after Ibn al-Zarqalluh, also known as Azarquiel. (Photo by NASA’s Lucy spacecraft showing the vast basin of Mare Imbrium. NASA/Goddard/SwRI/JHU-APL/Tod R. Lauer – NOIRLab) – Public Image (Archived)

The arrival of Islam in the West did not mean a decline in the study of the skies. On the contrary, Islam is a religion with an enormous amount of astronomic content. The field of astronomy related to religion (mīqāt) is quite extensive, considering that four of the five pillars of Islam are linked to astronomy (actually, all of them except for the profession of faith, the shahāda). The orientation of the Qiblah, the determination of prayer times, and the visibility of the moon, for example, are indispensable elements of day-to-day Muslim life. This does not mean that Islam is exclusively a religion of scholars: the Koran [Quran] specifically insists that religion poses no difficulties so that one cannot excuse oneself from it out of ignorance. The uniting of these two aspirations the pursuit of those guiding astronomical principles that are compatible with the will of popularization gave rise to a new tendency, popular astronomy, which became widely adopted. The faqih Ibn H. abīb (d. 852), in his Kitāb al-Nujūm, championed Arabic scientific tradition and, in adhering to the Koran, made it extremely clear what limitations existed in analyzing the firmament: the stars could be studied to guide the way, but not to carry out astrological calculations.

In Al-Andalus, the consequence of political decadence a by-product of the decentralization implied by the caliphate system was the proliferation of scientists dispersed throughout the taifas. Among the most famous of these was Maslama al-Majrīt.ī, considered to be the first truly Andalusian mathematician and scholar. Maslama represents the maturity of Andalusian astronomy for a variety of reasons, first and foremost for his founding of a real school that lasted over three generations. Among his direct disciples, Ibn al-Samh. (d. 1035) and Ibn al-S. affār (d. 1035), two significant authors who achieved a high level of popularity, also in the rest of Europe, stand out because their works on the construction and use of the astrolabe were translated into Latin. As for the contributions made by Masla- ma, it should be noted that he correctly predicted the conjunction of Saturn and Jupiter that was to take place in 1006/1007 and that would cause a great number of disasters, among them a change of dynasty. Maslama made use of important Eastern works that had already reached Al-Andalus, such as the Sindhind, by al-Khwārizmī, for which he authored a revision as did Ibn al-Saffār and Ibn al-Samh.

Fig. 2. Illustrations of one of the faces of Azarquiel’s equatorium, according to the Libros del Saber de Astronomía, compiled under the direction of Alfonso X the Wise (1221–1284), page 112 of the ms. of the Complutense University of Madrid Library. (Source)

Among the most important scientists in Al-Andalus was Ibn al-Zarqalluh, also known as Azarquiel (d. 1100) [3], who amassed the work that came out of the school of Maslama and expanded upon it. He deserves historical recognition for his labours as a theoretical astronomer as well as for his efforts as a designer of new scientific instruments (Fig. 1).

Ibn al-Zarqalluh went about studying the lunar and solar models, the length of the sidereal year, the eccentricity corresponding to the model of Mercury or Venus, and many other questions. In order to carry out his studies, he made diverse and lasting astronomical observations. In addition, illustrations of his instruments were preserved and later incorporated in the Libros del Saber de Astronomía, compiled under the direction of Alfonso X the Wise (1221–1284) (Fig. 2).

Ibn al-Zarqalluh distinguished between instruments used to observe shadow as projected upon a gnomon (such as the solar quadrants) and instruments used to directly observe the position of the sun and stars (such as the celestial sphere, the astrolabe, or the armillary sphere). He developed both types of instruments in original ways, especially the equatorium and the saphaea (Fig. 3).

The motivation behind the saphaea was that Ibn al-Zarqalluh was trying to improve the astrolabe. While inarguably the most widely employed instrument, the astrolabe had the disadvantage of requiring a specific plate for each latitude. If the plate corresponding to the latitude of interest was not available, the instrument was no longer useful or, at the very least, its measurements were inexact. This deficit led the Andalusians to design instruments with universal plates, such as the saphaea zarqāliyya, or its contemporary, the universal plate of ‘Alī b. Khalaf.

Fig. 3. Solar quadrant conserved in the archaeological site of Madinat az-Zahra. (Source)

The importance of these instruments includes the fact that they are the first documentation of the use of meridian stereographic projection. Later, in Nasrid Granada, Husayn b. Ahmad Ibn Bāso (m. 1315) [5] developed his own universal plate, building on the Andalusian tradition but also on the many contributions that had arrived from the East.

As Al-Andalus lost ground politically and academically, Maghreb became the focal point, although during this period many astronomers compiled tables (zij) derived from the Andalusian tradition. The likely reason for the continued Andalusian influence was that the most renowned of the Maghreb astronomers, Ibn Ishāq al-Tūnisī (fl. ca. 1193–1222), was an inheritor of the Azarchelian tradition. However, observations carried out during the 14th and 15th centuries by individuals such as Ibn ‘Azzūz al–Qusantīnī (m. 1354) resulted in the eventual abandonment of the calculations of Ibn al-Zarqalluh, as these astronomers determined their own numerical values for the planetary positions and the obliquity of the ecliptic…