Is it because, just as, when the light shines through an aperture with regular angles, the result is a round figure, namely a cone (the reason being that two cones are formed, one between the sun and the aperture and the other between the aperture and the ground, and their apexes meet), so, when under these conditions part is cut off from the orb in the sky, there will be a crescent on the other side of the aperture from the illuminant, that is, in the direction of the earth (for the rays proceed from that part of the circumference which is a crescent)?