Week 3 - of me reading Einstein's RELATIVITY the special and the general theory a clear explanation that anyone can understand.
Is anyone still out there? In chapter 4 we discuss the law of inertia -- a body (removed from other bodies ie gravity) moves in a uniform straight line. Got it.
But stars move in a giant circle. So, we can't use Euclidian co-ordinates to measure them because the law of inertia does not apply. So, if we must follow the law of inertia then we must use a different system -- we use a Galileian system of Co-ordinates. There is no picture. But I googled one and it seems pretty clear that I am coming to the end of my understanding. But I've also come to the end of this very short chapter which is less than a page long. I think Albert knew this next page turn would be rough. So I'm out of here!