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June 12, 2021

55: Mapping the Heavens

55: Mapping the Heavens

The Franks are answering life's big questions: where does God live? What causes lightning? What is our place in the universe?


In the last episode on the Carolingian Renaissance I talked about how the Franks expanded their knowledge on nearly every major subject. One area I didn’t manage to get to is astronomy. At the time, calendars and general knowledge of the heavens were fairly crude. In fact, there are no surviving Merovingian works dealing with astronomy, and most Greco-Roman knowledge of this science was lost. Scholars often couldn’t decide what day it was, meaning that different localities celebrated holy days at different times. This irked Charles who wanted uniform Christian worship across his empire. During his reign the king sponsored and standardized a new calendar to regulate feast days and ceremonies. From the late 8th to the early 9th century the Carolingians vastly improved their astronomical knowledge, charted all the constellations and developed complex mathematical theories to explain the movements of the moon and the five visible planets.

Before we get into astronomy, we need to look at what the Carolingians knew about the heavens. Frankly, it wasn’t much, since Greco-Roman knowledge on the topic was lost and the Merovingian monarchs didn’t patronize natural philosophers. Most Franks, and most Europeans for that matter, believed in a geocentric universe. In their view the Earth was the center of the cosmos and was stationary. Everything else revolved around the Earth, including the planets and the stars. The Franks adopted a Platonic view of the universe, holding that Earth was the point of purest objectivity, while the farther one went towards the stars, reality became more subjective. They believed that in heaven things were perfect in form and action. So, when the planets and stars revolved around the Earth they did so in a purely circular fashion. This is in contrast to Earth where forms and actions have been imperfect since the original sin of Adam and Eve.

Speaking of planets, most people believed there were only five, since those are the only ones visible with the naked eye. These planets are: Mercury, Venus, Mars, Jupiter and Saturn. The two outer planets, Uranus and Neptune, are only visible with a telescope, which wasn’t invented until 1608. Naturally, Uranus wouldn’t be discovered until 1781 by Englishman William Herschel, while Neptune wasn’t discovered until 1846 by Frenchman Urbain Le Verrier and his German colleague Johann Gottfried Galle.

Astronomy was a difficult subject to study since conservative Christians viewed it as a gateway to astrology. Saint Augustine condemned astrology as a pagan practice, whose followers attempted to divine God’s plan by falsely attributing power to the heavenly bodies. Naturally, astronomers had to condemn astrology and reassure the church that they were only working on mathematical principles. At the same time, astrology was incredibly popular among Carolingian aristocrats who wanted to divine their futures. At a time when half of all children died before the age of 10, and when plagues and famines could devastate communities without warning it’s understandable why people would do anything to protect themselves, including disobeying the church and resorting to borderline magic in order to read signs that might help them. As such, many nobles bought lunaria, lunar calendars which helped them divine if good or bad things would happen based on observations in the heavens, notably comets and eclipses. Horoscopes were probably also popular since manuscripts detailed the ascendancies of celestial bodies, which is the basis for horoscopes. This put astronomers in an awkward position because wealthy patrons sponsored them to learn astrology, but the church condemned these practices as heretical.

Carolingian astronomers faced many obstacles. They had very little foundation for their research and the church was incredibly suspicious of their work. Because of these challenges, 8th century Carolingian astronomy was mostly just observation. However, from the late 8th century to the 840s scribes copied books by Roman astronomers who developed complex theories of the cosmos alongside mathematical models for orbits. The Carolingians expounded upon these and created numerous diagrams and charts which revolutionized European astronomy.

Most of the following information I got from Bruce Eastwood’s book, Ordering the Heavens: Roman Astronomy and Cosmology in the Carolingian Renaissance. It’s a pretty thick read, but it is filled with beautiful pictures of Carolingian star maps, planetary diagrams, zodiac charts, and models of the universe, so buy it, put it on your coffee table and make people think you’re smart. According to Eastwood, there were four primary Roman natural philosophers whose works the Carolingians rediscovered. Between 800-820 the Franks popularized Macrobius’ Commentary on Cicero’s Dream of Scipio and Pliny the Elder’s Natural History. Macrobius’ work was the perfect intro to astronomy since it provided an orderly overview of the cosmos and was general enough not to stumble over mathematical insufficiencies in its theories. As we’ll see, the planetary orbits are far more complex than just regular circles and Macrobius’ work set some general guidelines without devolving into inaccuracies trying to solve all these problems. Pliny’s work went beyond Macrobius’ writings and offered more detail on the planets, comets and eclipses. He also provided rationale for planetary phenomena, eclipses and winds, which the Romans believed came from the heavens. Furthermore, Pliny provided explanations for irregularities in planetary motion where before there were only observations. In the 830s the Carolingians took the astronomical part of Martianus Capella’s Marriage of Philology and Mercury to explain why daylight hours changed during the year and why seasons had different lengths. Finally, in the 840s the Franks rediscovered Calcidius’ Commentary which offered a coherent philosophical and qualitative geometrical account of the cosmos.

Instead of doing a purely chronological approach, I think it would be more interesting to look at the ideas these thinkers had. First: what did they think the universe was made of? Each of these writers generally accepted the Greek idea that all substances were comprised of the four elements: Earth, Water, Fire and Air. But they disagreed about the existence of a possible fifth element they called ‘aether.’ Martianus Capella argued that there must be a fifth element, a divine wind that filled the heavens, allowing or even facilitating planetary movement and the movement of light. Capella did not accept the idea that space could be largely empty, nor did he accept that the perfect heavens could be filled with air like on imperfect Earth, hence why his theories required aether.

Macrobius disagreed. He argued that fire was the heavenly substance which descended to Earth. To Macrobius, air, earth and water were the Earthly elements. Fire came from the celestial bodies, giving life to the Earth, with the Moon as a transition between the Earth and the heavens.

Here we need to understand that while we may use the same words as the ancients, the meaning is often different. When the Classical Greek philosophers used their word for ‘fire’ they often meant something akin to ‘life-force,’ ‘animus’ or ‘energy.’ When the Greco-Romans wrote ‘fire’ they often didn’t just mean a chemical fire but any sort of power that imbued motion into an object. Some philosophers even theorized that the most extreme form of fire was lightning, which was the element of fire in its most pure and concentrated form. For this reason, the Greek god Zeus and his Roman counterpart Jupiter weren’t just primitive thunder deities. His control over lightning meant that he was the master of the universe’s animating force. So, the next time you’re binge-watching Avatar: The Last Airbender and wondering why the best firebenders can shoot lightning from their hands, now you know. These theories impacted astronomical ideas. Pliny the Elder argued that thunderbolts were actually discharges of energy from the planet Jupiter, that occurred when excessive moisture from Saturn met excessive fire from Mars.

Now that we know about their ideas regarding the substance of the cosmos, let’s talk about the heaven’s relationship to Earth. Macrobius believed that souls travelled across the cosmos, in contrast to orthodox Christianity. Over time Christians increasingly believed that the one God is a transcendental deity who exists beyond the realm of nature, as opposed to many old polytheistic gods which are a part of nature. If you ask a 21st century Christian where a soul goes when they die they’ll probably wonder why you’re bothering them, but after the initial awkwardness they’ll tell you that it doesn’t physically go anywhere but detaches from a physical body to go to a spiritual realm. Macrobius didn’t agree and he did not divide the physical and spiritual world. He theorized that souls emerged in the farthest heavens among the stars. Since they emerged in a perfect realm they were perfectly circular. Souls descended from the heavens to Earth where they entered into a head, which was roughly circular. When a person died the soul moved upwards where the planets, which were circular, received them. Circles were important. If you think about it, the sky itself is a circle, while the heavenly bodies appear to be circles to the naked eye, meaning, that everything beyond the clouds is circular. And if you think that heaven is literally above you, then heaven is nothing but circles. This is in contrast to Earth, where perfect circles rarely occur naturally.

Macrobius believed that the planets governed everything that happened below them. He avidly wrote on astrological elements such as on the zodiac. If you don’t know what the zodiac is, just look up into the night sky and imagine cutting it like a pizza into 12 different segments, each called a ‘house.’ Astrologers believe that when planets traveled through different houses that effects people on Earth. Macrobius didn’t specifically promote or teach astrology, but his writings on these elements meant that he probably dabbled in it and later Carolingians used his work to make horoscopes.

Pliny the Elder disagreed with Macrobius’ claim that the heavens governed the Earth. Pliny condemned divination and astrology, claiming God was perfect and didn’t change his mood on whims. Even though he argued that cosmic events do not cause events in human history but they do cause predictable effects on the environment. He believed that many celestial signs are prophetic though not determinative. The most important are eclipses and comets, which signify changes in rulers and kingdoms, or herald great battles. Meteors, multiple suns or moons, blood in the sky, also predict future bounty or catastrophe.

The Carolingian monarchs generally agreed with Pliny and regularly consulted astrological signs. By 798 Charles frequently conferred with Alcuin about portents for his empire. In the years before his death, chroniclers recounted numerous eclipses and other foreboding omens. Charles’ son Louis the Pious also consulted astrologers who connected heavenly signs to notable events. In 817 a series of comets appeared shortly before Pope Stephen IV’s death. In 818 a solar eclipse appeared before Queen Irmingard’s death. On 1 April 837 a chronicler known only as “the Astronomer” observed Halley’s Comet passing rapidly across 5 houses over a 25-day period. Louis was worried at such an unusual sign, so he fasted and prayed that night, then he and his court gave alms to the poor. Later, he hunted in the Ardennes and came back with quite a haul, and was convinced the danger had passed. Finally, on 5 May 840 there was a total solar eclipse. Shortly thereafter Louis fell ill and died the following month. While the church condemned astrology, the frequency of chronicles conflating astronomical events to worldly events shows that Carolingian monarchs ignored the religious interdiction on celestial divination in order to secure their futures.

Let’s end by talking about the progress of astronomical knowledge. I mentioned earlier how important circles were and now we’ve come full-circle. [drumroll sound]. I think I’m funny. Astronomers were obsessed with circles because, with the naked eye, everything in the sky is a circle. They further theorized that the cosmos was made up of concentric circles. The Earth was the circular center of the universe and the heavens could each be divided into their own circles. Pliny believed that Mercury inhabited the first circle, then Venus was in the second, then the Sun, Mars, Jupiter, Saturn and finally the stars. Each heavenly body revolved around the Earth in a regular circular motion.

However, there was a problem with this theory: the objects in the night sky don’t revolve in perfect circles. They frequently change speeds during their revolutions. Today we…well, not ‘we,’ but smart people with telescopes, know why these changes occur. First, the Earth isn’t the center of the universe, but a moving object. The other planets don’t revolve around Earth and instead we are two objects going on our own paths. Second, the planets don’t revolve in perfect circles but in ellipses, which is an elongated circle. Finally, gravity impacts the planetary movements. As the planets come closer to the sun they speed up, and conversely slow down as they move away from it.

Classical astronomers and their Carolingian admirers believed in a geocentric universe and had no concept of gravity and so they had to come up with ideas to explain the wild variations in planetary movements. The Greeks pioneered a concept called epicycles which are frequent miniature revolutions over a small area which occur while the planets’ large revolution is around the Earth. Imagine a child gets on a carousel, and the child is so happy that they’re dancing in circles while the carousel is spinning around. If you’re the exhausted parent watching them they might appear to be larger or smaller, and moving faster or slower depending on how close they are to you during their mini-rotation, while all the while the carousel is taking them around in a large rotation. That’s not how ancient astronomers viewed the planets but it’s the best metaphor I could come up with so let’s roll with it.

Looking back at this period you might want to say that the Carolingians were wrong in their theories. But science doesn’t work that way. It’s rare that any idea based on logic doesn’t lead to new discoveries, either because there is some merit to the idea or the idea is coherent enough that it takes a better idea to replace it. Since Albert Einstein’s Theory of Relativity we can say that most of Isaac Newton’s ideas were inaccurate, but Newtonian physics were more accurate than what came before. Furthermore, Newton’s idea of a mechanical universe inspired the future physicists who went on to prove him wrong. Likewise, many of these ancient Greco-Roman ideas seem like primitive superstition to us, but from a historical perspective we must recognize that they were better explanations than their predecessors. Furthermore, these theories inspired future generations to think logically. Pliny the Elder demonstrated that the cosmos followed an observable natural order. Martianus incorporated geometry into astronomy because he believed that celestial bodies were physical objects akin to those on Earth. He encouraged people to use mathematical reasoning to develop complex models that could predict their movement while explaining irregularities. Calcidius theorized that supposed ‘irregularities’ in the movements of celestial bodies were instead just undiscovered but logical patterns. During the Carolingian Renaissance scribes copied these old books and added countless diagrams, charts and mathematical equations which tested, corrected and improved upon Greco-Roman theories.

There is a commonly-held historical belief that astronomy was a lost art until Europeans acquired Arab texts in the 12th century but this is false. The Carolingians developed their own understanding of the cosmos so much that when later Europeans accessed advanced astronomical texts from Arabs they quickly understood them because they were already well-versed in astronomical theories and mathematical models. They pioneered more precise calendars, dating systems, created explanations for changing seasons and daylight hours, observed celestial phenomena and inspired generations to use mathematics to study space.

Surviving Carolingian astronomical manuscripts are concentrated largely in the Loire valley and written primarily in Old French. Hence, late Western Franks, who would become ‘French,’ were particularly interested in astronomy. It was these Franks and their students that charted the heavens and inspired generations to look upward.



Bruce S. Eastwood, Ordering the Heavens: Roman Astronomy and Cosmology in the Carolingian Renaissance, 2007.

Encyclopedia Britannica

Ed. Rosamond McKitterick, Carolingian Culture: Emulation and Innovation, 1994



I like to think that Macrobius had a younger brother named Microbius [boos], yeah yeah, I’ll see myself out.