Those who have visited the pyramids of Giza in person are always awe-struck by their size (particularly Khufu’s and Khafre’s pyramids). It’s difficult to capture on camera the pure gravity that you feel being in the presence of that many massive blocks of stone, stacked that high.
As many readers would know though, back when they were first constructed the pyramids would have looked even more impressive, as they were finished with casing stones made of polished limestone, smoothing the sides of the ancient landmarks and ‘painting’ them white, allowing them to brightly reflect sunlight.
But could this reflective coating also have sent sunlight from the pyramids to other sites of significance? Donald E. Jennings, a retired physicist from the Goddard Space Flight Center, noted that the high-quality Tura limestone used for the pyramid’s outer casings could have been polished to the point of enabling specular reflection (strong specular reflections can still be seen on the polished granite pyramidions of Amenemhet III and Khendjer), similar to that from a glass window, and wondered whether the Egyptians used this to good effect.
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.
Jennings was intrigued enough with the idea that he modeled specular reflections from the pyramid of Khufu and derived the annual dates and times when they would have been visible at important ancient sites on the Egyptian calendar, as well as with solar equinoxes, solstices and cross-quarter days. His investigation is documented in a new paper on arXiv.org, “Specular Reflection from the Great Pyramid at Giza“”
The sites Jennings included in his investigation included Heliopolis (the ‘City of the Sun’, home to the Temple of Ra), Djedefre’s pyramid, and Memphis (the capital of the Old Kingdom in Egypt) to the south of Giza. By modeling the path of the Sun, and how its light would have reflected from the pyramids toward those sites, he was able to pin down dates for when the effect would have taken place.
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 at Heliopolis. Imagine standing at Heliopolis in early February 2560 BCE looking southwest across the Nile valley. The recently completed giant pyramid, called the ‘horizon of Khufu’, gleams white and dominates the horizon. Suddenly, just before noon, the pyramid begins to brighten and is soon shining like a second sun, mimicking a sunset. the glare lasts some moments before dimming. For that brief time the great pyramid has controlled the sun, sending a piece of it to its home, the temple of Ra…it is a clear demonstration of the connection between your king and the sun god.
Jennings’ paper also calculates the times and places when the sun’s reflection was sent to the horizon, as well as noting that on the winter solstice, “the sun’s reflection from the south face of the Khufu pyramid was at 39.8˚, almost directly back on itself. In this arrangement the sun in a sense was ‘seeing’ its own reflection”. He notes however that, while this peculiar alignment was a result of the 51.8˚ slope of the pyramid’s side, it is unlikely that it was an intentional effect.
Furthermore, overall Jennings does acknowledge that he “knows of no ancient record of these displays” that he is hypothesising about, and “whether the great pyramids produced specular reflections cannot be known for sure” as without evidence from the archaeological record “we cannot be certain that the limestone casing was polished to a mirror finish”. As he previously pointed out, however, we do know existing polished granite pyramidions throw specular reflections, and it is believed that some pyramidions/capstones were gold-coated, which would have produced an intense reflection.
But, Jennings argues, “given the central role of the sun in their culture, it is probable that the Egyptians would have considered the solar specular effect in their architecture.” And perhaps the effect need not have even been planned into the architecture – its manifestation in the environment still would have been noted and perhaps venerated:
Unique relationships revealed in the reflections, even after the fact, could be taken as confirmation of divine provenance. Whether part of the original plan or revealed later as a consequence, specular flashes from the Great Pyramid, together with its ever-visible diffuse shine, would have been impressive at any distance, a stunning reminder of the magnificence of the Egyptian world.