Never mind the weeks, I'm sorry I brought them up, they are not that important. What is important is all the other stuff because those are absolute facts, not just shtuff we can make up on the fly. The planet will absolutely take a certain amount of time to go around its orbit, so will the moon, the second moon and everything else in our solars system. This is stuff that we can know with certainty. This is stuff anyone more advanced than hunter gatherers would know, and even most of them would either know or have a handle on the basics.