For hundreds of years, researchers have been puzzled by the mysteries of the pyramids of Giza, not only their mysterious voids and hidden chambers, but also how ancient Egyptians built such impressive structures without modern technology.
How the structures became perfectly aligned is one of the most confusing issues.
The square sides of the Great Pyramid of Giza are pretty straight.
The builders of the Great Pyramid of Khufu aligned the monument to the points with an accuracy of better than four minutes of arcs or one-fifteenth of one degree.
In a way, all three of the largest Egyptian pyramids are remarkably aligned, in a way you wouldn't expect to see from an era without drones, blueprints, and computers.
All three pyramids have the same way of error, they are rotating slightly counterclockwise from the cardinal points.
Many hypotheses exist as to how they did this, but it is never clear how these worked.
Dash came up with a simpler idea. The Egyptians could have used the autumnal equinox to achieve perfect alignment, according to his study.
The length of the day and night are the same when the plane of Earth's equator passes through the centre of the Sun's disc.
It was assumed that the measurement of the equinox wouldn't provide enough accuracy, so it was overlooked as a possible alignment method.
Dash showed that there is a way this could have been done using a gnomon.
Dash did his own experiment, starting on the first day of the fall equinox in 2016 and using a gnomon to cast a shadow.
He tracked the point of the shadow at regular intervals. At the end of the day, with a taut piece of string wrapped around the pole, he created an almost perfect line running east-west.
The Indian circle method can be seen in action below.
Dash, JAEA.
The shadow's tip will be found on the equinox by the surveyor, who will find it in a straight line and almost perfectly east-west.
The degree of error is slightly counterclockwise, which is similar to the slight error found in the alignment of the Red pyramid at Dahshur.
Dash said that the same thing should work in Egypt.
Dash explained to Live Science that all ancient Egyptians would have needed to align the pyramids.
He said that the Egyptians would have been able to work out the fall equinox by using the summer solstice as a reference point.
Although his paper shows that this technique could have been used to align the pyramids, we don't have any solid evidence that was actually the case.
The Egyptians left us little clues. There are no engineering documents or architectural plans that show how the ancient Egyptians aligned their temples or pyramids.
The idea that a simple mapping of shadows during the fall equinox could have been used to align some of the most recognizable ancient structures is interesting.
The paper can be read in its entirety in The Journal of Ancient Egyptian Architecture.
The first version of this article was published in February.
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