C. S. Lewis on the Size of the Medieval Cosmos
The dimensions of the medieval universe are not, even now, so generally realized as its structure; within my own lifetime a distinguished scientist has helped to disseminate error. The reader of this book will already know that Earth was, by cosmic standards, a point -- it had no appreciable magnitude. The stars, as the Somnium Scipionis had taught, were larger than it. Isidore in the sixth century knows that the Sun is larger, and the Moon smaller than the Earth (Etymologies, III, xlvii‑xlviii), Maimonides in the twelfth maintains that every star is ninety times as big, Roger Bacon in the thirteenth simply that the least star is 'bigger' than she. As to estimates of distance, we are fortunate in having the testimony of a thoroughly popular work, the South English Legendary: better evidence than any learned production could be for the Model as it existed in the imagination of ordinary people. We are there told that if a man could travel upwards at the rate of 'forty mile and yet som del mo' a day, he still would not have reached the Stellatum ('the highest heven that ye alday seeth') in 8000 years.
These facts are in themselves curiosities of mediocre interest. They become valuable only in so far as they enable us to enter more fully into the consciousness of our ancestors by realizing how such a universe must have affected those who believed in it. The recipe for such realization is not the study of books. You must go out on a starry night and walk about for half an hour trying to see the sky in terms of the old cosmology. Remember that you now have an absolute Up and Down. The Earth is really the center, really the lowest place; movement to it from whatever direction is downward movement. As a modern, you located the stars at a great distance. For distance you must now substitute that very special, and far less abstract, sort of distance which we call height; height, which speaks immediately to our muscles and nerves. The Medieval Model is vertiginous. And the fact that the height of the stars in the medieval astronomy is very small compared with their distance in the modern, will turn out not to have the kind of importance you anticipated. For thought and imagination, ten million miles and a thousand million are much the same. Both can be conceived (that is, we can do sums with both) and neither can be imagined; and the more imagination we have the better we shall know this. The really important difference is that the medieval universe, while unimaginably large, was also unambiguously finite. And one unexpected result of this is to make the smallness of Earth more vividly felt. In our universe she is small, no doubt; but so are the galaxies, so is everything -- and so what? But in theirs there was an absolute standard of comparison. The furthest sphere, Dante's maggior corpo is, quite simply and finally, the largest object in existence. The word 'small' as applied to Earth thus takes on a far more absolute significance. Again, because the medieval universe is finite, it has a shape, the perfect spherical shape, containing within itself an ordered variety. Hence to look out on the night sky with modern eyes is like looking out over a sea that fades away into mist, or looking about one in a trackless forest -- trees forever and no horizon. To look up at the towering medieval universe is much more like looking at a great building. The 'space' of modern astronomy may arouse terror, or bewilderment or vague reverie; the spheres of the old present us with an object in which the mind can rest, overwhelming in its greatness but satisfying in its harmony. That is the sense in which our universe is romantic, and theirs was classical.
-- The Discarded Image (Oxford: Oxford University Press, 1964), 97-9