Egypt's Great Pyramid of Giza is an ancient feat of engineering, with the monument almost perfectly located along the cardinal points — north, south, east and west.
Archaeologists have long been puzzled about how ancient Egyptians managed to achieve the near-perfect alignment, although now they believe to have solved the mystery, news.com.au reports.
When Egyptian pharaoh Khufu had the Great Pyramid of Giza constructed almost 4500 years ago, builders were able to achieve such precision by using the autumn equinox — halfway between the summer and winter solstices when day and night are of equal length.
Glen Dash, an engineer who studies the Giza pyramids, recently explored the emerging theory about the position of the 138m-tall structure in a paper published in the Journal Of Ancient Egyptian Architecture.
"The builders of the Great Pyramid of Khufu aligned the great monument to the cardinal points with an accuracy of better than four minutes of arc, or one-fifteenth of one degree," he wrote.
Mr Dash added that the pyramid of Khafre (also located at Giza) and the Red Pyramid (located at the site of Dahshur) share the same high degree of accuracy in regards to the cardinal points.
"All three pyramids exhibit the same manner of error; they are rotated slightly counterclockwise from the cardinal points," he wrote.
For his research, Mr Dash placed a rod on a wooden platform and marked the location of the its shadow throughout the day during the autumn equinox.
"On the equinox, the surveyor will find that the tip of the shadow runs in a straight line and nearly perfectly east-west," he wrote.
Mr Dash said the tilt of Earth on the equinox allows the shadow to run in this east-west direction, with a slight degree of error found counterclockwise — similar to the error found in the Great Pyramid, Khafre Pyramid and Red Pyramid.
Despite the experiment being conducted in Connecticut, Mr Dash is confident the technique would work have worked in Giza if the Egyptians determined the day of the autumn equinox by counting forward 91 days after the summer solstice.
Even though his theory holds merit, Mr Dash admits the Egyptians could have also used other methods involving the sun or stars to align the pyramids.
"The Egyptians, unfortunately, left us few clues. No engineering documents or architectural plans have been found that give technical explanations demonstrating how the ancient Egyptians aligned any of their temples or pyramids," he wrote.
However, he does believe his method has the advantage of being less complicated than other theories.
"It is hard to imagine a method that could be simpler, either conceptually or in practice," he wrote.