Specular Reflection from the Great Pyramid at Giza
The pyramids of ancient Egypt are said to have shone brilliantly in the sun. Surfaces of polished limestone would not only have reflected diffusely in all directions, but would also likely have produced specular reflections in particular directions. Reflections toward points on the horizon would have been visible from large distances. On a particular day and time when the sun was properly situated, an observer stationed at a distant site would have seen a momentary flash as the sun's reflection moved across the face of the pyramid. The positions of the sun that are reflected to the horizon are confined to narrow arcs in the sky, one arc for each side of the pyramid. We model specular reflections from the pyramid of Khufu and derive the annual dates and times when they would have been visible at important ancient sites. Certain of these events might have coincided with significant dates on the Egyptian calendar, as well as with solar equinoxes, solstices and cross-quarter days. The celebration of Wepet-Renpet, which at the time of the pyramid's construction occurred near the spring cross-quarter day, would have been marked by a specular sweep of sites on the southern horizon. On the autumn and winter cross-quarter days reflections would have been directed to Heliopolis. We suggest that on those days the pyramidion of Khafre might have been visible in specular reflection over the truncated top of Khufu's pyramid.