The year and the month do have a celestial component. The seven-day week
is a purely abstract convention that does not repose on any celestial phenomenon.
You seem to discount G-d, the creator of the universe.
He told us that there are seven days to the week.
b'shem Y'shua
No, I don't discount the Genesis account and the religious traditions of Judaism, adopted by the rest of the world as the seven day week.
My point was that there is no NATURAL component of the week.
One need have no religion at all to come up with the month and the year: these are celestial phenomena. You figuring them out by watching the stars, the seasons and the moon. Winter and the moon cycles are hard to miss, and practically everyone, everywhere, figured them out.
That we HAVE a week, at all, is because of Jewish religion, at least as far as we know. There isn't any NATURAL, observable seven-day cycle in the Cosmos. This didn't come out of people all around the world staring at something obvious and counting the days, like the lunar and solar calendar did.
The week came PURELY out of a human tradition, without a natural component. Judaeo-Christians and Muslims believe that this tradition came from a divine revelation. The rest of the world thinks that it came out of the West and adopted it for convenience sake (just as it is 2005 in formally atheist China, because it's convenient to use the world calendar).
I'm not arguing that the week doesn't have a divine source.
I am merely stating that the source for the week is NOT something purely natural. It's either pure human tradition, or human tradition created in response to a divine revelation. The month and year are logical subdivisions of the calendar. The week is not logical, it is traditional. People differ in what they think about the source of the tradition.
When we look at the Noachide laws, which Genesis tells us God laid upon the whole world, we do not see a Sabbath Day. The Sabbath was laid by God upon the Jews, specifically, through the laws of Moses. It applied to Jews, not to everybody else.