I'm sure there must be a simple explanation to this...
I'm not an expert, but one of the concepts I understand is that the speed of light is constant and is independant of the motion of the observer. Why is it then, that red-shift occurs when observing distant galaxies which are moving away from us?
Another concept I am given to understand is that the speed of light CAN vary according to the density of the medium in which it is travelling. My own simplistic logic therefore, would conclude that red-shift is the result of light travelling massive distances through sparsly occupied(but not empty) space.
Can someone put me on the right track with my thinking please?
Ian