With a fairly broad range of interest in arts and sciences, it's quite unusual for me to be brought up short by something. But one of the points that Michael Ward brought out in "Planet Narnia" did.
There were seven medieval/ancient "planets". The word "planet" means "wanderer", and the planets were the objects that moved around in the sky, relative to the fixed backdrop of stars. So the list doesn't correspond to the current catalogue of planets (with or without Pluto) - it consisted of the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn. These planets represented different deities, and (Ward argues) these different deities themselves really represent different aspects of a single Deity, certainly within Medieval Christian literature.
What I'd never considered before was that each of the seven days of the week is, at least in Northern Europe, associated with a different one of these planets. It's a little masked, as our names of days make reference to the Norse "images" of these planets. Sunday is the Sun's day, Monday is the Moon's day, and Saturday is Saturn's day. Thursday is Thor's day - Thor being the Norse ruler of the gods, the equivalent of Jove/Jupiter. The Mediterranean god is more visible in the French word "jeudi" and the Spanish "jueves". Friday is Venus's day (Frig/Freia) - again, in French, we have "vendredi" and in Spanish "viernes". Wednesday is Woden's day, the equivalent of Mercury ("mercredi") and Tuesday is Tiwes' day - Mars' day ("mardi", "martes").
What intrigued me about this is that these names of days, and their identification with these different planets/deities, either spread across cultures at some stage or predated the development of the languages. It would be interesting to know just how widespread a seven day week was, and how widespread the association with these planets actually is, and whether the seven days were always associated with those planets. If anybody has any insight into this, I'd love to hear it.