The reason why we see the full face of the moon (when it is opposite to the sun) is the effect of diffraction of light around the spherical surface of the earth. Correct? There can't be another explanation since without diffraction, the moon should be dark just like when it is on the same side as the sun. So this lends naturally to the confirmation of the diffraction theory of light? Hence prior to "Fresnel's spot" experiment, this simple observation should have at least convinced a lot of people to the wave theory of light. Newton was unconvinced about the wave nature all his life? Or did he accept it after Fresnel's spot and how did he reconcile it with his particle theory of light. In any case, how did he explain seeing a full moon prior to Fresnel's spot and diffraction?