Is there a link between the seven-day week and the visible planets, as the names of the days indicate? I’d seen it suggested that this connection dates back to the Babylonians, as they had a seven-day week and had identified and named the planets. If Wikipedia is accurate, however, these two were first associated by the Greeks. As far as I know, the Babylonians never named the days of the week; they were just numbered. Since every Babylonian month began with the full moon, I suppose the length of the week was probably roughly determined by the phases of the moon. It was common in the ancient Middle East for one day of every week to be held as holy, a tradition that remains in the Abrahamic religions today.
The Babylonians did apparently name the planets after gods in their own pantheon, which the Greeks later renamed after their Olympian equivalents. From nearest to farthest from the Sun (and not counting Earth, obviously), the five visible planets were called Nabu, Ishtar, Nergal, Marduk, and Ninurta. To the Greeks, they were Hermes, Aphrodite, Ares, Zeus, and Kronos; and of course the names we use now are the Roman versions of those same gods.
The Greeks also named one day of the week after each planet, plus the Sun and Moon. And as I indicated yesterday, Germanic languages later adapted the names of the days to reflect their own gods. I’m not sure whether they also used the names for the planets themselves; it seems likely, but I haven’t seen any specific evidence of such. I’ve already explained why Odin being Mercury doesn’t make a whole lot of sense to me, but even more striking is that Saturday retains the name of a Roman god. The thing is, I’m not entirely sure why the planet Saturn has that name. The explanations for the others are pretty well-known: Mercury appears to move quickly, Venus is the brightest and therefore most beautiful celestial object (other than the Sun and Moon), Mars is red like blood, and Jupiter is the biggest and hence the king. And if we look at the Babylonian name, it’s Ninurta, not a god we know a whole lot about. He was apparently an earth god worshipped at Lagash, and was not particularly in vogue by the late Babylonian period. As such, there are some definite similarities to Kronos/Saturn, a god of farming who was said to have been the ruler of heaven before being deposed by Zeus/Jupiter. So who would be the Norse equivalent? Well, Freyr was a fertility god, so he might work.
Alternatively, we could use Odin’s father Borr, another deity we know little about and was part of an earlier generation. Of course, “Borrday” would better apply to Monday than to Saturday. (Get it? “Bore”? Get it? Awww, you’re no fun.) Why whoever came up with the Germanic names for the days didn’t make either of these associations isn’t clear.