Medieval Cosmology
Sed quid ergo positiones sidereas caelique leges enumerem, cum ad oculos pateant universa?
"But why should I catalog the positions of the heavenly bodies and the laws of heaven when all lies open to view?"
— Bernardus Silvestris, Cosmosgraphia 4.5, trans. Winthrop Wetherbee
Tungol sceal on heofenum / beorhte scinan swa him bebead Metud.
"Stars in the heavens must shine, as the Lord has ordered it."
— Maxims II (Anglo-Saxon)
Caeli enarrant gloriam Dei, et opera manuum eius adnuntiat firmamentum.
"The heavens declare the glory of God, and the firmament proclaims his handiwork."
— Psalms 18:1
The cosmological system of Western Europe in the Middle Ages had been inherited directly from the Ptolemaic/Aristotelian system of Greco-Roman antiquity. Ptolemy’s Almagest itself was translated into Latin in the twelfth century by Gerard of Cremona, and its model of the universe had been earlier transmitted indirectly through several standard school-books of the Middle Ages, including works by Macrobius, Martianus Capella, Boethius, and Isidore of Seville. Within the Islamicate world, Arab scholars had kept alive knowledge of Aristotle’s Physics and his De Caelo, producing many commentaries on it. And it was through Arabic translations that the Physics, as well as Aristotle’s other major cosmological work, On the Heavens, became known to scholars in the Latin West starting in the twelfth century. Famous medieval philosophers such as Thomas Aquinas, William of Ockham, and Nicholas Oresme all produced commentaries on Aristotle’s cosmological works, but they also drew upon original astronomical speculation of Islamic scholars like Alfraganus and others. (It is no surprise, then, that most common names for the brightest stars—Altair, Vega, Arcturus, etc.—are Arabic in origin.)
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The Ptolemaic/Aristotelian model of the universe was geocentric: the Earth, being composed of, well, Earth and thus the heaviest object in the universe, was naturally located at the center, while all the other heavenly bodies revolved around it. In contrast, the current model of the Solar System is heliocentric, with the Sun in the center.
Following Aristotle and Ptolemy, the heavenly bodies—no material distinctions were made between stars and planets—occupied a series of concentric spheres around the Earth. The Moon was located in the closest sphere to the Earth, hence the frequent designation of terrestrial matters as “sublunary” (“beneath the Moon”), a label that long outlasted the gradual adoption of the heliocentric Copernican system in the sixteenth and seventeenth centuries. It was in the sublunary realm of Earth that the Four Elements—Earth, Air, Water, and Fire—contend with one another in ceaseless motion. The sublunary realm, unlike the heavens above, was subject to inexorable and often unpredictable change.
Beyond the Moon, and in order of increasing distance from the Earth, were the spheres of the other heavenly bodies: Mercury, Venus, the Sun, Mars, Jupiter, and Saturn.* The sphere of Saturn was itself surrounded by an eighth sphere—the sphere of the Fixed Stars, so called because, in contrast to the “stars” we now refer to as “planets,” the Fixed Stars remain in stationary positions relative to each other, forming Constellations, most of them identical to the constellations recognized by modern star-gazers. The sphere of the Fixed Stars was also known by some writers as the Firmament or the Crystalline Sphere.
Beyond the sphere of the Fixed Stars, Ptolemy had postulated an invisible ninth sphere, the Primum Mobile—the “First Moevere” of Chaucer’s Knight’s Tale—the sphere whose rotation in a chain of causation sets in motion all the other spheres. For Aristotle and Ptolemy, who both believed that the universe was eternal and not the result of some moment of creation in Time, the notion of the Primum Mobile functioned as a sufficient “first cause.” However, the Judeo-Christian idea of God as the Creator necessitated a different understanding of the Aristotelian Primum Mobile. Among medieval poets, Dante Alighieri presents perhaps the most vivid explanation in his Paradiso:
Following Aristotle and Ptolemy, the heavenly bodies—no material distinctions were made between stars and planets—occupied a series of concentric spheres around the Earth. The Moon was located in the closest sphere to the Earth, hence the frequent designation of terrestrial matters as “sublunary” (“beneath the Moon”), a label that long outlasted the gradual adoption of the heliocentric Copernican system in the sixteenth and seventeenth centuries. It was in the sublunary realm of Earth that the Four Elements—Earth, Air, Water, and Fire—contend with one another in ceaseless motion. The sublunary realm, unlike the heavens above, was subject to inexorable and often unpredictable change.
Beyond the Moon, and in order of increasing distance from the Earth, were the spheres of the other heavenly bodies: Mercury, Venus, the Sun, Mars, Jupiter, and Saturn.* The sphere of Saturn was itself surrounded by an eighth sphere—the sphere of the Fixed Stars, so called because, in contrast to the “stars” we now refer to as “planets,” the Fixed Stars remain in stationary positions relative to each other, forming Constellations, most of them identical to the constellations recognized by modern star-gazers. The sphere of the Fixed Stars was also known by some writers as the Firmament or the Crystalline Sphere.
Beyond the sphere of the Fixed Stars, Ptolemy had postulated an invisible ninth sphere, the Primum Mobile—the “First Moevere” of Chaucer’s Knight’s Tale—the sphere whose rotation in a chain of causation sets in motion all the other spheres. For Aristotle and Ptolemy, who both believed that the universe was eternal and not the result of some moment of creation in Time, the notion of the Primum Mobile functioned as a sufficient “first cause.” However, the Judeo-Christian idea of God as the Creator necessitated a different understanding of the Aristotelian Primum Mobile. Among medieval poets, Dante Alighieri presents perhaps the most vivid explanation in his Paradiso:
La natura del mondo, che quïeta / il mezzo e tutto l'altro intorno move, / quinci comincia come da sua meta; / e questo cielo non ha altro dove / che la mente divina, in che s'accende / l'amor che'l volge e la virtù ch'ei piove ... e come il tempo tegna in cotal testo / le sue radici e ne li altri le fronde / omai a te può esser manifesto ["The nature of the universe, which holds / the center still and moves all else around it, / starts here as from a boundary line. / This heaven has no other where / but in the mind of God, in which is kindled / the love that turns it and the power it pours down ... How time should have its roots in a single flowerpot / and its foliage in all the others / may now become quite clear to you" — Paradiso 17.112-120, trans. Robert Hollander and Jean Hollander
The observed regularity of the motions of the various “stars” across the heavens validated the idea of an orderly, ultimately benevolent God governing the cosmos. Observation of the heavens was further enabled by the introduction of the astrolabe, an instrument likely derived from Arabic models by as early as the tenth century. (The astrolabe, incidentally, loomed large in the medieval imagination: Geoffrey Chaucer wrote a Treatise on the Astrolabe for his son Lewis, and Abelard and Heloise named their love-child Astrolabe.)
Such accuracy also encouraged the practice of astrology, that is, the casting of predictions based upon the positions of the stars at particular points in time. Lest moderns believe that the medievals were uniformly credulous, it should be noted that plenty of people in the Middle Ages were skeptical of such astrological predictions. As William Langland writes, Astronomiens |
alday in here arte faylen / That whilum warnede men byfore what sholde byfalle aftur (Piers Plowman, C-text, XVII.97-98). Christian teaching likewise discouraged astrological fortune-telling, and authorities as weighty as Cicero, Augustine of Hippo, and Isidore of Seville had expressed reservations about both the efficacy and morality of astrological speculation. Nonetheless, certain medieval writers reveled in the poetic and fictional possibilities of an astrologically-meaningful world. Dante's words are peppered with astrological references, and at least two of Chaucer's Canterbury Tales (The Knight's Tale and The Miller's Tale) pivot around astrological insights.
Whether or not medieval writers and thinkers embraced astrology as a mode of prediction, certainly the understanding that the various planets could influence events on earth or one's personality was widespread. Chaucer's Wife of Bath, for example, considers that Venus me yaf my lust, my likerousnesse, / And Mars yaf me my sturdy hardynesse (Canterbury Tales III.611-12). For a deeper look at the symbolism and associations of the various planets, see here.
The publication of Nicholas Copernicus’s De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) in 1543 effectively demolished the medieval geocentric model of the universe, though it would take many decades before Copernicus’s heliocentric model was widely accepted.
Whether or not medieval writers and thinkers embraced astrology as a mode of prediction, certainly the understanding that the various planets could influence events on earth or one's personality was widespread. Chaucer's Wife of Bath, for example, considers that Venus me yaf my lust, my likerousnesse, / And Mars yaf me my sturdy hardynesse (Canterbury Tales III.611-12). For a deeper look at the symbolism and associations of the various planets, see here.
The publication of Nicholas Copernicus’s De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) in 1543 effectively demolished the medieval geocentric model of the universe, though it would take many decades before Copernicus’s heliocentric model was widely accepted.
* Martianus Capella, in his influential On the Marriage of Philology and Mercury (ca. 420 CE), speculated that Mercury and Venus in fact revolved around the Sun and not the Earth, a canny precursor to the later discoveries of Copernicus.
Further Reading
- Dante Alighieri, Convivio: A Dual-Language Edition, ed. & trans. Andrew Frisardi (Cambridge University Press, 2017)
- Marcia L. Colish, Medieval Foundations of the Western Intellectual Tradition, 400-1400 (Yale University Press, 1997)
- Edward Grant, Planets, Stars, and Orbs: The Medieval Cosmos, 1200-1687 (Cambridge University Press, 1994)
- C. S. Lewis, The Discarded Image: An Introduction to Medieval and Renaissance Literature (Cambridge University Press, 1964)
- Macrobius, Commentary on the Dream of Scipio, trans. William Harris Stahl (Columbia University Press, 1990)
- Martianus Capella, The Marriage of Philology and Mercury (Martianus Capella and the Seven Liberal Arts, Vol. 2), eds. William Harris Stahl & E. L. Burge (Columbia University Press, 1992)
- Ptolemy, Ptolemy's Almagest, trans. G. J. Toomer, rev. ed. (Princeton University Press, 1998)
- George Saliba, A History of Arabic Astronomy: Planetary Theories During the Golden Age of Islam (NYU Press, 1995)