Sometimes the simplest explanation is the best one. That’s what an archaeologist is proposing for Egypt's great pyramids, suggesting the Earth’s position around the Sun was enough to give these structures their odd alignment.

The Great Pyramid of Giza, along with another at Giza and one at Dahshur, are all remarkably aligned along the cardinal points – north, south, east, and west. However, experts have struggled to explain why this is the case, as the Egyptians did not have access to tools to accurately determine these directions such as a compass.

Writing in the Journal of Ancient Egyptian Architecture, archaeologist Glen Dash proposes an Occam’s razor approach. He suggests the Egyptians used the autumnal equinox, when the Sun is directly above Earth’s equator and daylight hours equal those of night, to achieve this.

“It produces results that match the actual alignments of the largest pyramids of the pyramid age in magnitude and direction,” Dash wrote in his paper. “It is also the ‘Occam’s razor’ candidate. It is hard to imagine a method that could be simpler either conceptually or in practice.”

To come to this conclusion, he performed an experiment at his home in Pomfret, Connecticut, using a tool known as a gnomon. Sort of like a sundial, this involves placing a vertical rod in the ground to project a shadow on the ground and, by tracing out its path, an observer can use a piece of string to draw a line from east to west.

Although there is no evidence the Egyptians used this method, Dash said his experiment showed it would be possible to use it for the pyramids. On September 22, 2016, the autumnal equinox, he tracked the position of the gnomon’s shadow, producing a line with a small margin of error.

This margin was similar to those of the pyramids, which are each slightly misaligned counterclockwise to the cardinal points. He said that using a large platform to trace the shadow, the Egyptians could have extended the line to lay a baseline for the pyramids.

“The equinoctial solar gnomon method appears to be workable,” he wrote. “It joins the list of methods the Egyptians might have used to align their pyramids.”

Without any documents or architectural plans, we may not know for sure how the pyramids were constructed in this way. Others have suggested that bright stars in the Big Dipper and Little Dipper constellations, or even the Pole Star, could also explain the alignment. But if Dash is correct, then the simplest explanation may trump them all.