The Stoics were not interested just in ethics, even though that was the crucial aspect of their very practical philosophy. In going through the various chapters of the Cambridge Companion to the Stoics, we have looked at aspects of their “logic,” including moral psychology and logic proper; and our explorations of their “physics” has led us through discussions of natural philosophy and more recently of medicine. Today is the turn of Stoic astronomy.
The corresponding chapter in the Cambridge collection is authored by Alexander Jones, which begins with an overview of Greek, and particularly Hellenistic, astronomy, especially centered around Eudoxus’ model of a celestial sphere surrounding a stationary Earth. The model also accounted for the movement of the Sun and the planets by hypothesizing a number of additional, invisible, rotating spheres. It is important to note that already by the II century BCE Eudoxus’ system was known to be inadequate to explain actual astronomical phenomena.
What about the Stoics? Zeno, the founder of the philosophy, wrote a book called On the Whole, in which he explained solar and lunar eclipses respectively as due to the passing of the Moon between Earth and the Sun and the Moon’s traversing the shadow projected by the Earth. Strike two points for the Stoa.
But then again strike one against it because of Cleanthes rejection of Aristarchus’ conjecture that it is the Earth that moves around the Sun, and not vice versa. Cleanthes went so far as to make the very un-Stoic (in my mind) suggestion that the authorities should prosecute Aristarchus for impiety!
According to Jones, a systematic presentation of Stoic astronomy is found in Cleomedes’ Kyklikê Theôria Meteôrôn (“Theory, involving circles, of the things in the heavens”), which builds on, and yet differs from, Aristotle’s physics. According to Cleomedes, the cosmos is made of a finite sphere contained in an infinite void. The Earth is at the center of it, surrounded by water, air and then aether. Outside all of this are the planets, each revolving according to its own motion.
Cleomedes sharply criticized Epicurus, for instance for the latter’s idea that the Sun is really only “as big as it appears” (about a foot in diameter), but even his estimates are crude by comparison to what had already been produced by Aristarchus and Hipparchus (the latter had arrived at a figure for the distance between the Moon and the Earth, using two different methods, within 30% and 17% of the actual one).
So, even though the Stoics were concerned with astronomy, their opinions — just like the ones they held on medicine — were not exactly cutting edge.
From a modern standpoint, however, what is more puzzling is the Stoics’ interest in astrology. Then again, Jones is very careful in disentangling several meanings of the term for the ancients: i) the Greek tradition of correlating weather and seasonal patterns with changes in the heavens; ii) the Near Eastern take, which was concerned with the interpretation of omens; and iii) the Hellenistic and Roman approach of making predictions based on the instantaneous position of heavenly bodies.
Cicero tells us that Panaetius was skeptical about astral omens, but also that he was rather exceptional among the Stoics. Tacitus, for his part, says that the Stoics were skeptical about so-called astrological determinism: fate (or universal cause and effect) does determine everything that happens, but astrologers are not thereby capable of making reliable predictions based on their charts. It’s also worth noting that later Roman Stoics hardly mention astrology at all.
It is interesting, finally, to comment briefly on Stoic geography. Here the two major authors are Posidonius and Strabo. Posidonius was interested in, and conceived of, the earth very much as a physical, not just a geometric, system, and was concerned with very modern topics, such as climatic zones, tides, seasons, etc..
Strabo was more cautious about speculating about the causes of geographical phenomena, since their causes are “hidden,” thereby posing strict epistemic limits to what one can say with confidence, given the status of knowledge at the time.
Interestingly, and in perfect Stoic fashion, Strabo’s approach to geography was “shaped by the ethical motivation he ascribes to the geographer, whose efforts aim at eudaimonia by providing information useful in all human undertakings, and not least in those of wise rulers.”
Why would a modern Stoic be interested in any of the above, other than in terms of purely historical curiosity? For two reasons, I think. First off, it is always good to remind ourselves of just how much the ancients got wrong, especially when it comes to science. There is a tendency, in some quarters, to venerate ancient wisdom and to gloss over the plain inadequacy, by modern standards, of much of their knowledge of the world. Stoicism is a live philosophy because the Stoics got something fundamental about ethics and human nature right, not because of their astronomy, medicine, or whatever. (The same, I think, could be said of other still viable philosophies, like Buddhism.)
Second, I find it challenging for a modern mind that the Stoics thought of all knowledge — including that of their “physics” (i.e., natural science and metaphysics) and their “logic” (i.e., logic, epistemology and cognitive science) — as valuable not in its own right, but because it served ethics, the study of how to live one’s life.
As a modern scientist who has spent decades investigating basic questions in biology, with no clear connection to practicalities and the betterment of humanity, I have always taken for granted that of course curiosity for curiosity’s sake ought to be encouraged and, most importantly, funded at the tune of billions of dollars annually. But I’m not so sure anymore. More and more I find the Stoic challenge compelling: we are here now, and we have huge problems to solve. Why shouldn’t all our efforts and resources be devoted to use our ingenuity in order to improve our condition? I don’t think there are easy answers to be had, besides platitudes about the “long term” usefulness of basic science, which more and more sound like self-serving rationalizations to my mind. It seems to me an open and rather urgent question in modern society.