that's my guess too, I am looking for a (simplified) model to visualize that.
But I am stuck to this: there are three bodies,sun,earth and moon; two of them on the ecliptic plane; in case of a new moon the angle separation sun-observer-target of the projection of the moon on the ecliptic plane should be 0 in my thinking; but it is not. At what point I am wrong? Spherical trigonometry?
sorry for a not so clear description ...
