Which effect are you talking about? I'm talking about two observers, one at 45N, one at 45S, looking at the Moon at the same time, with each seeing the crescent in different positions, separated by approx 90 degrees. You seem to understand what I'm getting at. You seemed to confirm it with your red arrows on the moon graphics in Reply #23 ... - 90 degrees difference in latitude, 90 degrees difference in the crescent
I'm not talking about the passage of the Moon over time, over the course of a night, or any other period. If both observers look at the same time, we have already seen, from mooncalc, how their views would differ. You agree that if a camera is held in one position, looking at a crescent moon, then moved around its axis, the crescent is shifted by 90 degrees or so. With two observers separated by 90 degrees of latitude, can you see how this shift of the camera applies, assuming both observers keep their cameras upright?