The aperture in Stone 8, the capstone, is regular. It appears to display the qualities of a superellipse, or 'squircle'. I am not convinced of this by any means, but the physics of such a figure and its consequent optical properties are the subject of study. Viewing straight up through it reveals a patch of sky in which the sun and moon never appear, the angle is too great. However, when viewed at an angle the sun is observable through the 'slot'.