Plausible Explanations – Why Are There 7 Days in a Week?

Here’s the game: come up with a plausible explanation for everyday facts and phenomena.  The key is plausible, something you could tell a group of people and they would actually believe it.  These are joke answers, obviously, but make the jokes believable if you can.  Winners of best answer will be declared the winner (and if there is enough interest to do it again, can pick next time’s fact).

This week’s topic:

  • Why are there 7 days in a week?

This is not a place for politics, which is why I’m asking for science and social stuff like measurements and whatnot.