Moon's surface. Composite image of two opposite lunar phases. The image at left is part of a waning moon and the image at right is part of a waxing moon. The black area at centre is the terminator, the boundary between the illuminated part of the moon and the unilluminated area. This image shows that there is a 10-35 degrees overlap in longitude in the terminator area, allowing the craters seen along its edge to be viewed in light falling from opposite angles.