Staring at the heavens: Astronomy in medieval Islam

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"To the medieval Muslim astronomers and scientists, the heavens provided a heady language of admiration and thoughtful reflection. Numerous verses in the Quran, the earliest surviving text from early Islam, instruct believers to ponder over the signs of God scattered all over the heavens"

Few today would disagree that there is something mystifying and humbling about the heavens and the starry night sky.

Like us, our ancient predecessors found much delight in their nocturnal sky gazing. But for ancient religionists and scientists, there was more to it than sheer curiosity and admiration.

To stare at the heavens was to communicate with the gods and reach into the realm of metaphysics. The practice belonged to astrology and good-natured magic.

We are told as much in the ancient Greek novel Aethiopica by Heliodorus. When the Egyptian priest admonishes the young Theagenes, he informs him that to study the heavens is to tread the path of wisdom and honesty:

There is a vulgar science and one which, I might say, crawls on the surface of this earth… The other, my son, is truly wise, of which the vulgar form is an illegitimate version masquerading under the same name… It is conversant with heavenly things, lives with the gods, and partakes of the higher nature, considering the moving of the stars and gaining a knowledge of the future therefrom, far removed from these earthly evils and directing all things to the honesty and commodity of men.

Fast forward several centuries into the world of Islam and you will find similar sentiment.

To the medieval Muslim astronomers and scientists, the heavens provided a heady language of admiration and thoughtful reflection.

Numerous verses in the Quran, the earliest surviving text from early Islam, instruct believers to ponder over the signs of God scattered all over the heavens, expressed in several places in the Muslim scripture, as the following verses show:

Verily in the heavens and the earth are signs for those who believe (45:3).

He causes the dawn to break, and has made the night for rest, and made the sun and the moon to travel with precision. That is the design of the Almighty, All-Knowing. And He is the One Who has made the stars as your guide through the darkness of land and sea. We have already made the signs clear for people who know (6.97-8).

He is the Lord of the heavens and the earth and everything in between, and the Lord of all points of sunrise. Indeed, We have adorned the lowest heaven with the stars for decoration (37:5-6).

Later generations of Muslim thinkers went a step further. They came up with ingenious ways to study and reflect on the heavens.

They built observatories that helped them discover constellations and distant stars – that is why most of the present-day constellations bear Arabic names, such as Acrab, Caph, Furud, Lesath, Maaz, Thuban, and Zurac – devised instruments to map out the night sky, penned treatises on celestial and longitudinal movements, put forward arguments for a spherical earth and heliocentric planetary model, and paid significant attention to the sun and moon to arrive at precise descriptions of lunar and solar eclipses, among many other things.  

Let us consider some notable examples. As early as the ninth century CE Muslims constructed observational posts and built observatories.

Two observatories were founded during the reign of the Abbasid caliph al-Maʾmun (r. 813-833): the Shammasiyyah, in Baghdad, and the Qasiyun, in Damascus.

They operated as solar and lunar observational posts, resulting in a set of planetary tables, longitudinal movements, and astronomical handbooks, known as the Mumtahan Zij.  

It was during research conducted at the Shammasiyyah Observatory in Baghdad that the Persian Muslim scientist Habash al-Hasib (who died in 869 CE) calculated the circumferences, diameters, radii, and other matters related to the Earth, Sun, and the Moon.

His findings, published in his The Book of Bodies and Distances are remarkably close to modern science. Al-Hasib calculated the Earth’s circumference to be 32,444 km (modern science says 40,000 km) and the Moon’s circumference 9538 km (modern science says 10921 km). His calculations of the Sun’s circumference, however, were quite wide of the mark.  

In the subsequent centuries, Muslims went on to build another seven observatories. Among the most notable were the Maraghah and the Samarqand observatories.

The Maraghah Observatory was constructed in 1259 CE in what is today the East Azerbaijan Province of Iran.

It was designed by the formidable philosopher, theologian, and mathematician Nasir al-Din al-Tusi (who died in 1274). It functioned as a centre for astronomical research, housing a library, equipment storage, and several circular observational posts to observe stars and planetary objects.

The Samarqand Observatory was built in the 1420s CE by the erudite mathematician and astronomer Ulugh Beg (who died in 1449). It took inspiration from the Maraghah model while relying on the scholarly insights of Ulugh Beg in trigonometry and spherical geometry.

"Owing to the many commentaries on the heavens and the marvels of the universe, it appears that medieval Muslim societies became assiduously invested in understanding the great wonders of the stars and deep space"

Eager to develop their observational activities, medieval Muslim astronomers took a keen interest in what we might today call cosmography. The Epitome of Introductory Theoretical Astronomy is but one glaring example.

It was written by the thirteenth century CE astronomer and physician Mahmud al-Jaghmini. The work is in Arabic, and it contains introductory explanations on how celestial movements work, along with discussions on the nature of bodies and, more specifically, the Earth.

Undoubtedly popular, owing to the numerous commentaries it received in Arabic and Persian (and by the plethora of extant manuscripts of the work), the work typifies a medieval example of public-facing scholarship aimed at educating the laity and astronomy enthusiasts.

In fact, owing to the many commentaries on the heavens and the marvels of the universe, it appears that medieval Muslim societies became assiduously invested in understanding the great wonders of the stars and deep space.

A representative example of a new genre devoted to such understanding is the aptly titled The Wonders of Creatures and the Marvels of Creation by Abu Yahya Zakariyah al-Qazwini (died in 1283 CE).

Immensely popular, the work contains scores of detailed drawings of planets and well over 400 miniature paintings. It follows a neat hierarchical order of the cosmos, including celestial spheres, the 12 signs of the Zodiac, stellar constellations, and observable celestial phenomena, such as eclipses.

Straddling between the rational and the imaginative, al-Qazwini demonstrates fecund creative abilities in the sections on celestial cosmology. These include discussions of time and space, angels and demons, and the realm of divinity.

Steering away from the imaginative and more towards the scientific, medieval Muslims laboured hard to come up with means to measure and observe celestial happenings in the vast night sky.

Theoretical innovations included the Tusi-Couple, named after the aforementioned Tusi. It was a mathematical device containing a small circle undergoing rotary motion inside a larger circle, known as a 2-cusped hypocycloid.

"Steering away from the imaginative and more towards the scientific, medieval Muslims laboured hard to come up with means to measure and observe celestial happenings in the vast night sky"

According to contemporary authorities of Arabic science, such as George Saliba, the Tusi-Couple provided a “solution for the latitudinal motion of the inferior planets and later used extensively as a substitute for the equant introduced over a thousand years earlier in Ptolemy's Almagest”, a celebrated work of ancient astronomy.   

It was a disciple of Tusi named Muʾayyad al-Din al-ʿUrdi, who died in 1266 CE and hailed from Syria, that left an indelible mark on Arabic science by becoming arguably the most celebrated instrument maker in medieval Islamic astronomy.

Al-ʿUrdi wrote a text called Treatise on Observations devoted to the engineering of equipment required in observational posts, some of which were unique inventions by al-ʿUrdi himself.

"Muʾayyad al-Din al-ʿUrdi, who died in 1266 CE and hailed from Syria, left an indelible mark on Arabic science by becoming arguably the most celebrated instrument maker in medieval Islamic astronomy"

Every observational post, we are told, requires the following instruments, as summarised by Petra G. Schmidl: a mural quadrant for altitudes, an armillary sphere for ecliptic longitude and latitude, a solstitial armilla for the obliquity of the ecliptic, an equinoctial armilla to work out the entry of the Sun into the equatorial plane and its path at the equinoxes, and a dioptrical ruler to measure the apparent diameter of the Sun and the Moon, and what is known as the azimuth ring to determine the altitude.

These are but a few representative examples to highlight the medieval Muslim innovations in astronomy. Much more could be said of other major astronomers whose contributions are too vast to recollect in a few words.

These would include the profound studies of the eleventh century CE genius Abu Rayhan al-Biruni, arguably the greatest polymath in the history of Islam, and who argued for heliocentrism and the Earth rotating around its axis, as well as be one of the first to break down the hour sexagesimally into minutes, seconds, thirds, and fourths.

Dr Ahab Bdaiwi is University Lecturer in Arabic and Medieval Philosophy and Late Antique Intellectual History at Leiden University.  His research ventures into an array of subjects and themes in Islamic studies but oftentimes revolves around the disciplines of intellectual and religious history, philosophy, theology, and oriental manuscripts in Islamicate societies.

Follow him on Twitter: @abhistoria