Astrology in the Middle Ages

In literature made before the year 1100, astrology is rarely, if ever mentioned. Histories, if they deal with such knowledge, are more concerned with the discovery of ancient Roman texts than they are with discovering any “new” knowledge of the sky. Yet just over 250 years after the turn of the 11th century, Chaucer writes to his son in his Treatise on the Astrolabe, “these ben observances of judicial matere and rytes of payens, in whiche my spirit [ne] hath no feith.” What changed between these two eras? What would result in almost nobody talking about astrology in one, and in another an author who frequently uses astrology as a plot device stating t his actual lack of belief in the effects of the stars, all within an instruction manual on star-observation? This is the Big Question that I hoped to answer in this research paper. Originally, I was planning on trying to characterize the nature of astrology in the 12th century. However, I realized that much of what was being done in the era was a reaction to translations of Arab material, recovery of Greek texts, and travel. So instead, I will primarily be focusing on the intellectual history of 12th century astrology, as well as how the influx of new ideas influenced the adoption of new technology and the creation of original works of astronomical significance.

The most confusing point to a modern reader when faced corpus of astrological research is a simple question: what is astrology? In his Etymologiae, Isidore of Seville stated that “Astronomy concerns itself with the turning of the heavens, the rising, setting, and motion of the stars, and where the constellations get their names. But astrology is partly natural, and partly superstitious.” This is the definition that has carried through today, and has been significantly strengthened by the rise of modern astronomy that widened distance between the two disciplines’ academic rigour. Yet, for much of history, the two were closely intertwined and often largely interchangeable.

Astronomy, from the Greek astronomos, meaning star-arranging, is, naturally, the science of observing the placement of the stars. The etymology of astrology, from the same word for star, and “-logia” meaning the study of something, means that astrology is the study of the stars and their effects. So, it was necessary for people in the 12th century to use astronomia to conduct astrologia, and vice-versa. Medieval astronomy worked by calculating positions of the planets along the zodiac, or its more technical term, the ecliptic: the apparent path of sun across the sky. This path is broken down into 30 degree increments, which are the 12 signs of the zodiac. Planets are assigned to each of these increments, called houses, and are each imbued with a complex system of relationships. A planet is said to be in dominance if it’s in its own house, in detriment if in a house hostile to it, in exultation if in a house friendly too it, and in fall if in its opposite house. The varied relationships between these celestial bodies, in turn, are thought to influence people on earth.

Patristic authors writing in late antiquity took a particularly dim view of astrology. In the City of God, St. Augustine writes that that “which they call the horoscope, it is either disproportionately small to the diversity which is found in the dispositions, actions, habits, and fortunes of twins…”. This distaste for astrology on both moral and common-sense grounds largely defined the way that Western Christianity would see astrology and those who practiced it for centuries to come. Easter, the most important of all Christian Feasts at the time, changed days each year and needed to be calculated according to the equinox via a process called computus. This requires observation of the moon in order to place Easter on its correct day in the lunar calendar.

The only significant advancement in this area was by Dionysius Exiguus, who made improvement to existing computus tables in 525 that was later adopted in the Frankish Court and the rest of Western Europe.5 Those skilled in computus were encouraged to come to the Carolingian palace at Aachen, but since the Dionysian tables only allowed for the placement of the moon and sun along the zodiac, no level of astrology or astronomy close to that of antiquity could be practiced. One ninth century computus manual contains a diagram for determining good and bad days entitled “the sphere of Pythagoras,” but, again, this only required the coordinates of the sun and the moon. While the “Dark Age” narrative is often overstated in terms of popular conceptions of the medieval world, it is true that the availability of astrological texts dropped almost as sharply as astrological discourse — so much so that it’s more productive to discuss the few pieces that survived in the West than to discuss those that would later be recovered.

Macrobius is primary known today for his Saturnalia, a nostalgic work on the lives of great Roman pagans. Yet he was more known throughout the middle ages for his commentary on the Dream of Scipio, a story which is itself contained within the sixth book of Cicero’s republic. This story, as well as Macrobius commentary, preserved Ptolemaic structures of the universe: the earth with planetary spheres around it, all surrounded by a Prime Mover.7 Martianus Capella’s Marriage of Mercury and Philology was another important late Latin source. In it, he presented an allegorical marriage of the god Mercury (intelligence) to Philologia (learning, but literally the love of letters). Given to them as gifts are seven handmaidens who will serve the newlyweds. These are the trivium: Grammar, Dialectic and Rhetoric, and the quadrivium: Geometry, Harmony, Arithmetic, and our subject, Astronomy. Astronomy gives the couple a long, rigorous crash course in the motions of the heaven. She names all the stars and planets, and describes their motions. Even the zodiac is accounted for. This work comprises the bulk of technical astrological knowledge that would exist until late 11th century.

Boethius was also an important writer of Late Antiquity. He is suspected of having written a major work on astrology that may or may not have survived very long due to contemporary prejudices. Regardless, such a text is lost. His Consolation of Philosophy, while dealing primarily with the notion of man’s relation to fate and the cosmos at large, was also responsible for popularizing Platonic cosmology. In it, Lady Philosophia urges him to look at the stars, and says that “the heavens are less wonderful for their foundation and speed than for the order that rules them.”

The idea that the heavens had an ultimate order to them provided a safe harbor for astrology, as anything the stars could conceivably tell humans had already been createdd by divine providence. These three writers, combined with Calcidius translation of Plato’s Timaeus — one of the foundational texts of Platonic thought — formed everything of note that the West had to work with in terms of astrological thought. This dearth of new materials is one possible reason that Early Medieval astrology never developed anything new in the field for centuries. The Carolingian Renaissance served to better circulate the texts that did exist, but still failed to replicate the interest that the world of antiquity had in the stars. Instead, that tradition was carried on in the Islamicate world that was experiencing a golden age of learning, much of which was fueled by new research done into Greek thought.

Some of the most important work to be done in the field of astrology during the 12th century was not by original thinkers, but by translators. The 12th century marks the start of the great recovery of classical knowledge, as well as a diffusion of new Islamicate philosophy into Europe. Unsurprisingly, the hotspots of translation came from cultural contact zones. First and foremost was Andalusia, followed closely by Italy. One of the most important figures of this era was John of Seville, a converted Jew Mozarab who translated many highly influential astrological texts.

Among them are al-Fughani's Rudiments of Astrology, a summary of Ptolemy’s Almagest, al-Khayyat’s Book of Birth, a guide to making horoscopes, and the Flowers of Abu Ma’Shar, a lesser collection of writings from the famous astrologer.10 Another translator of Arab works was Hermann of Carinthia, who was on Peter the Venerable Quran Translation team, but was also notable for translating Abu Ma'Shar’s Great Introduction. This work in particular is especially important to 12th century astrological thought. In an already effective and influential astrological manual, Ma’Shar rationalizes astrology in a very Aristotelian way. Astrology isn’t “prediction” any more than not touching fire for fear of being burned is “prediction.” Fire has been hot, is hot, and will be forever be hot. As such, what the stars have to say has always been revealed. All people need to do is examine them. At this point, there was also a significant recovery of Greek texts, mostly through Arab channels. Gerard of Cremona and Plato of Tivoli were both prodigious translators, and brought to Europe the extremely important works of Ptolemy, the Almagest and the Tetrabiblos, respectively. Gerard was also instrumental in the translation of astrological tables, but those will be discussed later.

Not all of the 12th centuries most important students of Arab astronomical knowledge were from Andalusia or Italy. Some, like Adelard of Bath, came from the periphery. Not much is known about Adelard’s history, save for his works that can be dubiously dated. The Pipe Roll for the royal exchequer in 1930 confirms that he was receiving four shillings and sixpence from the sheriff of Wiltshire, something that Thorndike thinks suggests his service to the king. In his Natural Questions, he describes his reunion with friends in England during the reign of Henry I after a long period spent studying abroad. One of his nephews asks him to share “something new from my Arab studies,” so he begins a series of Platonic dialogues about a variety of natural phenomena, many of them pertaining to astrology. In an earlier work, De eodem et diverso, he also takes up the view of the stars as “superior animals,” and says that humans can look into the future by observing current natural happenings, even in dreams.

These constitute some of the first original astrological writings to appear in Europe for over 600 years. However, Adelard was also a prodigious translator. He gave Europe a Latin edition of Euclid’s Elements and, importantly, translated the astronomical tables of al-Khwarizmi in 1126. These were the first complete set of tables (i.e. a full description of the positions of stellar bodies on certain dates) to enter Europe. Astrologers found this table very difficult to use, however, as it used the mythical mountain of Arim (actually the Indian capital of Ujjain) as a median and used the hegira epoch and calendar to reckon time. To fix the situation, Plato of Tivoli translated the Toledan Tables, which were themselves the work of several Toledan Arab and Mozareb astrological researchers who fashioned new tables that used Toledo as a median.

An important concrete advancement in astrology during the 12th century was the popular adoption of the astrolabe in Europe. The first students of the astrolabe crossed the Pyrenees to study with Islamic scholars at the end of the 10th century. One such student was Gerbert of Aurillac, later Pope Sylvester II, who was known to have used the astrolabe and the armillary sphere as teaching aids. Even though the translations of such texts as de mensura astrolabia and De utilitatibus astrolabii had been translated by the mid 11th century, there aren’t very many records of their use until the very end of the 11th century. On 18 October 1092, prior Walcher of the Abbey of Malvern used an astrolabe to determine the exact time of a lunar eclipse, which he had seen in Italy the previous year. This marks the first use of the astrolabe in Europe as a tool for research and measurement, even if it was just to mark an important event in Walcher’s life.

With the inundation of the 12th century learned community with astrological knowledge came several original works in medieval astrological philosophy. Some, like Adelard’s aforementioned works, were original transmissions of Islamicate ideas to a European audience, but others were sufficiently original so as to capture not just the attention of European academics, but the imagination of its writers. One in particular influenced literature at a level beyond all the rest: Bernardus Silvestris. The date of writing for his most important work, the Cosmographia, is unknown, but a marginal note tells us that he performed it in front of Pope Eugenius III while he was was traveling in France in 1147. In it, Natura (nature), Noys (divine providence), and Hyle (primordial matter) hold a dialogue discussing the nature of the cosmos and how it relates to mankind. His imagery is highly original, and in many cases is in danger of contradicting Christian theology. He describes stars as “gods who serve God in person.” Between the divine and the earthly is the mediation of “the divinity of the stars.”

Rather than an obscure method of interpreting God's will, the stars are worthy of praise themselves, for they are the next best thing to divinity. The work greatly influenced writers and thinkers, such Hildegard of Bingen, Vincent of Beauvais, Dante, Chaucer, Nicholas of Cusa, and Boccaccio, whose annotated copy we still have today.19 This long intellectual history, culminating in the European adoption of astrological ideas in the 12th century, is why Dante feels the need to constantly reference the stars, even while in the depths of Hell. It is important to note that, upon his escape from, his final thoughts are not of god, or the hope of salvation, but of the stars, saying “E quindi uscimmo a riveder le stelle.” “It was from there we emerged, to once more see the stars.

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