How did ancient Egyptians tell the exact day and night of the summer and the winter solstices, or the equinoxes of spring and autumn? How could they tell the days when the flooding of the River Nile, Egypt’s lifeline, were approaching? How could they note the lunar cycles of the Moon ruling women’s menses? Did they know the approximate distance between the Earth and the Sun? Did they have markings for each passing day on the covering slabs of the Great Pyramid – removed since antiquity?
The following article is a summary of some of the highlights of his findings:
The Giza Pyramid Complex map (CC BY-SA 3.0)
Giza has four important structures. The lengthwise axis of the Sphinx faces the true east, aligned with the three pyramids of Khufu, Khaefre and Menkaure. The base planes of these exact geometrical structures are precisely aligned to north, south east and west. Khufu’s and Menkaure’s pyramids have three satellite pyramids each, aligned to the four directions. There is a straight line between the big Khaefre pyramid and the small ones south of it.
The Sphinx is on the east of the site map of Giza. The exact date when it was built is unknown to archaeologists, but we know that it was reconstructed around 1500 BC with a new layer of stone slabs. The stone slabs covered up and hid erosion marks running lengthwise on the Sphinx, which according to Geologist Robert Schoch, had developed five to seven thousand years before the reconstruction.
The head of the Sphinx was possibly made at the same time as the pyramids of Giza, but there are controversies surrounding the question whether the head was re-carved from the original stone or whether it was replaced by a new one.
The Great Sphinx of Giza. (CC BY-SA 3.0)
The most interesting part of the Sphinx, however, is the direction of its head, which points exactly to the East with the sun rising exactly above it every year, on March 21st. Furthermore, standing behind the Sphinx and looking into the same direction, East, time can be tracked at night through the movement of the constellations. A constellation from this viewpoint moves one degree every 72 years, and a completely new constellation takes its place every 2,160 years. Given that there are twelve constellations, a total circle of each twelve are completed every 25,920 years.
Dimensions of the Giza Site Plan in Royal Egyptian Cubits (© Andras Goczey. Measurements from J.A.R. Legon, ‘The Plan of the Giza Pyramids’, Archaeological Reports of the Archaeology Society of Staten Island, Vol.10 No.1. New York, 1979.)
In 2000, J.A.R. Legon measured up the site plan of the Giza pyramids using the standard ancient Egyptian measurement, the royal cubit.
The Giza-pyramids and Giza Necropolis, Egypt, seen from above. (Public Domain)
The relationship between the apex of the pyramid of Khafre and the low terrain point of the Khufu pyramid is important as it indicates where the sun rises on the 21st of June, which is the date of the summer solstice. The tangent angle is easily calculated using Legon’s measurements. The length of the adjacent side, 455.5 cubit divided by the length of the opposite side, 858.5 cubit, equals to 0.53, which is 27.9° tangentially. This gives us the angle between the summer solstice and the straight line to the East. Measuring that same angle down from the same line gives us the winter solstice, where the sun rises on the 21st of December. The line indicating the winter solstice hits the exact corner of Kentkawes pyramid the same way the summer solstice line hits the corner of Khufu pyramid.
Sumerian Clay tablet made with a cylinder seal. (Source)
Sumer clay tables were made couple of hundred years before the structures of Giza, depicting the moon cycle. In the top right corner in this particular image, there is a large moon depicted, representing the night, with seven smaller moons to its right, symbolizing the cycle of the moon. The number seven is crucial to the moon cycle as there are seven days between the new moon, the first quarter, the full moon and the last quarter. The Menkaure pyramid was designed to show the same moon cycle.
Pyramid of Menkaure, Egypt. (CC BY-SA 2.5)
Viewed from Earth, the Moon is fully dark at new moon; and its entire surface is lit at full moon. Half of its disk is lit at the first quarter, then 14 days later at the last quarter. Sitting between the satellite pyramid G3a and the large pyramid of Menkaure, facing the south, the moon moves from east to west. When the moon is exactly above the G3a satellite pyramid, it is precisely the new moon. After seven days, when it hits the G3b it signals the first quarter. Another seven days later, when it hits the G3c satellite pyramid it is full moon. Further seven days later, when it hits G3b again, the moon is in the third quarter.
The Moon Cycle signaled by the three satellite pyramids of Menkaure. (© Andras Goczey)
However, the exact time between two full moons is 29.53 days, so the exact difference between the four points in the cycle is not 7 but 7.3825. This small difference causes a little shift in every moon cycle, but it sets back to the exact position over 19 years. The orbiting time of the Earth for 19 years is 19×365.25 = 6,939.60 days. If one divides that with 29.53 (the number of days between two full moons), the result is 235,0017439. So 235 moon cycles have to pass for the Menkaure pyramid and its smaller satellite pyramids to signal the four cycle stages in their exact position.
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An interesting depiction of 14 days/rays. Akhenaten and Nefertiti under the solar rays of Aten (Source)
Another interesting thing about Menkaure is that besides signaling the moon cycles, it also can serve as an indicator of the female menstrual cycle. Perhaps many Egyptian women used it to track their 28-day cycle.
The Khufu pyramid has two rows of stone slabs around it, which differ from all the other ones, according to a measurement conducted by Petrie in the 1880’s. These two rows are made up of around 60 cm tall stone slabs, which mark exactly the one fifth of the pyramid and also the height of its three satellite pyramids. When the Sun rises from the East every day, the satellite pyramids cast shadows onto the East side of Khufu. These shadows show cardinal dates: the summer solstice on the 21st of June, the winter solstice on the 21st of December and also the equinoxes about the 22nd of September and the 21th of March.
The Pyramid of Khufu, or Great Pyramid (Nina Aldin Thune/CC BY-SA 3.0)
Out of three satellite pyramids, Hetepheres is the most important one, located closest to the North. On the 21st of June, the shadow of Hetepheres’ apex hits exactly the edge of the pyramid at the level where the two rows of 60-centimeter-tall stone slabs are. Every day its shadow moves 55-70 cm to the North, until the 21st of December, when it reaches the furthest point from the edge of the pyramid. This movement marks 182 days so it is possible that the Khufu pyramid and its satellite pyramid were used to mark the days of the year. The other two satellite pyramids— Meritetes and Hanutsen— signal these dates in a similar fashion, allowing for a more accurate time keeping system.
Khufu Pyramid measurements (© Andras Goczey)
Hungarian architect András Gőczey is author of a book that covers the subjects above set to be published in English this year. You can see more about this topic in his video:
By Andras Goczey; Translated by Luca Goczey