Part of Your World: Mapping Medieval Planets
Blog post for MORROIS
by Laura Moncion
For a project that seems straightforward enough, MORROIS’s task of mapping medieval romances has raised a number of thorny methodological questions. One of these is the question of how to account for planets.
References to planets can be found infrequently in medieval romances. So far, the references are to ‘Earth’ which can nest into ‘world.’ This actually poses another problem. In the Getty Thesaurus of Geographic Names (TGN) database we’ve been using to track our place names, there are separate TGN identifying numbers for ‘Earth’ and for ‘world.’ Earth is listed as a planet, an identifiable material space. World is listed as a facet, an element of the database itself under which all other terrestrial phenomena are nested. We have so far been using the TGN for ‘world,’ but the other possible classifications of ‘Earth’ begs a couple of questions.
Would including planets in our list of place names be an imposition of our present views onto medieval texts? The 20th and 21st century fascination with missions to Mars, for example, shows that we see planets as places that we can visit and even colonize. Would medieval people have thought of planets as spaces that they could inhabit? Would they have considered planets in the same way that they considered Sandwich to be a place, or Rome, or the Orient?
There is evidence to show that medieval people did consider planets to be spatial, material entities. Bartholomew the Englishman’s treatise De rerum proprietatibus (1240), like Ptolemy, Macrobius, Isidore of Seville, and Bede before him, even assigned the planets properties that mirrored the properties of terrestrial beings. For example, Mars was classified as hot and dry, and Saturn cold and dry, “pale and of an evil disposition.” Both Jupiter and Venus were classified as hot and wet, and Mercury “radiant and keeps pace with the Sun… thus it is rarely perceptible.” Planets were also able to have an effect on the human body: physical and personality traits could be predicted based on which planet presided over your birth. According to Bartholomew, Jupiter’s influence would give you beautiful eyes, fine teeth, and a babely round beard.
So, what did medieval people think planets were made of? Typically, ether. Bartholomew defines ether as “something beyond the lunar globe that is of a separate nature from the nature of the inferior elements.” Ether was thought of as a substance neither heavy nor light, without density, neither divisible nor corruptible – a “fifth essence” that admitted to none of the flaws of the other four. It was apparently uniform, unchangeable, moving in a continuous circular motion around the messy, retrograde Earth.
However, there is a problem with ether. The very fact that people could see planets moving around in the sky meant that ether, this near-perfect substance, was in fact not uniform. If it was, there would be nothing but flat, dark sky, without planets or stars to pick out from it. So, what makes a planet? Alexander of Aphrodisias argued that celestial bodies could possess attributes to distinguish them the one from the other, but in order to avoid the earthly cycles of generation and corruption, the planets would not admit to their attribute’s opposite. For example, the sun would possess hotness but never coldness. More popular than Alexander’s theory was the idea of density and rarity: that more or less visible planets were just denser or flimsier clusters of ether. Raphael Aversa, and later Mastrius and Bellutus, refined the idea of density by proposing that planets existed on a spectrum of opacity and diaphaneity – relying on the human eye’s perception, rather than an incalculable density.
If planets are made of ether, a material substance that nevertheless differs from material substances on Earth, where do they fit in the medieval world? As it turns out, they are part of it. The scholastic definition of the world is a four-part hierarchy: first, the ‘world’ is everything that exists, including God, intelligences, as well as celestial and terrestrial entities. The next level down is the ‘world’ as everything except God; the third level is the ‘world’ including the celestial bodies (planets and stars, etc) and the Earth. Only the fourth and final definition considers ‘world’ to be limited to the Earth. Planets belonged with the Earth because they were considered to be bodies, just bodies made of a higher substance.
What does this mean for mapping planets? First of all, it suggests that our classification of ‘Earth’ under ‘world’ is legit, since planets can be considered as part of a medieval ‘world.’ It also suggests that medieval planets were not considered to be material places in the way that we think of them. Planets were so extremely other to medieval people that they were made of a substance with which no one on earth had interacted. Planets were more likely to be figured as godlike, personified influences on people’s lives than as places to be visited, or to receive visitors from.
 Edward Grant, Planets, Stars, and Orbs: the Medieval Cosmos, 1200-1687 (Cambridge: 1994) p.469
 Grant p.424
 Grant p.138