Episode 31: We Need to Talk About Khufu

July 5, 2023

Before getting back into Egyptian astronomy proper, we start by looking at Nabta Playa, a site of megalithic activity in the Nubian desert during the late neolithic. Then we turn to the megaliths the Egyptians are best known for \u2014 the pyramids. The pyramids have remarkably precise alignments to the cardinal directions and the techniques the Egyptians used to set these alignments remains a mystery. Finally, we look at the largest of the pyramids, Khufu's pyramid, whose so-called ventilation shafts have a possible astronomical connection.


Good evening and welcome to the Song of Urania, a podcast about the history of astronomy from antiquity to the present with new episodes every full moon. My name is Joe Antognini.

Well last month we took a fairly broad overview of Egyptian history and geography and started to get into the astronomy of ancient Egypt by looking at their cosmology and the ideas they had about the beginning and end of the universe. This month we’ll continue to dive into Egyptian astronomy, but before we really get into it I wanted to talk about a topic that I perhaps should have discussed last episode just before getting to Egypt itself. This is a site called Nabta Playa and it’s one of the more remarkable megalithic sites not only in the Sahara but in entire world. Now, Nabta Playa is a little ways south of the city of Aswan which sits on the first cataract of the Nile, so strictly speaking, it’s really a Nubian monument rather than Egyptian, so if I were very strict about policing the boundaries of the subjects of each episode, it wouldn’t quite fit in to an episode on Egyptian astronomy. But there’s decent evidence that at least some of the people who built the monuments at this site later migrated north into Egypt proper, so when we’re going this far back in time, these distinctions are a little arbitrary.

Now, unlike a monument like, say, Newgrange, which we discussed back in Episode 28, Nabta Playa isn’t a single megalithic structure. Rather it’s a site that was the center of megalithic activity for about two millennia, starting around 5500 BC and lasting until around 3400 BC. This range of time might ring a bell from back in Episode 29 when I was talking about the megaliths of the Saharan desert, because this range lines up with the time frame that other megaliths were constructed in the Sahara, which in turn corresponds with the period over which the Sahara dried out and was transformed from arid grasslands to desert.

This region was inhabited by a people who are generically known as the Cattle Herders, and one of the first clues that the Cattle Herders considered this a special place is the fact that they buried cattle there. Nabta Playa has the largest density of cattle bones anywhere in the Nubian desert. What makes this particularly unusual is that the neolithic Cattle Herders did not, as a rule, slaughter their cattle, much like the pastoralists of the region today. Cows were much too valuable to be slaughtered and eaten for their meat — instead they were kept alive for as long as possible for their milk and their blood. Getting the milk is straightforward enough, but for the blood roughly once a month they would cut a cow’s vein, fill up a vessel with the blood, and then patch up the wound, at least if modern day Maasai practices are any indication of how it was done in the neolithic. But the cattle bones at Nabta Playa indicate that the animals there were slaughtered, which would have been a rather significant affair. In fact, the oldest tumulus at Nabta Playa, dating back to around 5300 BC, contains the skeleton of an entire young cow, which was an exceedingly valuable sacrifice for a pastoralist to make.

Archaeologists haven’t only found the bones of cows at Nabta Playa. There are also a number of human skeletons buried there as well, all of which were placed on their sides in a crouching position, oriented with their heads towards the west and facing south. Based on these skeletons archaeologists have been able to infer that the people who lived in this region during the Neolithic were generally of good health, especially when compared to the skeletons of the later sedentary Egyptians.

Well the Nabta Playa site contains about 30 megaliths, but three in particular stand out. The best known is a megalith called Calendar Circle. Now, calling this structure a megalith is maybe overstating things a bit. Perhaps it’s more appropriate to just call it a lith. It’s a circular arrangement of stones only about 4 meters across and the stones that make it up aren’t all that large, they’re all about 20 to 70 centimeters in length, so you could hold them in your hand quite easily. Several of these stones were put standing on their end. In fact, setting aside any astronomical connections, one of the most remarkable things about Calendar Circle is how well it stayed intact for nearly seven thousand years. With something like Stonehenge you can see how it stayed up over the years. The stones are just huge! You’d have to be really motivated to tear part of it down, or there would have to be some truly apocalyptic weather event to really impact the structure. But with Calendar Circle anyone could just come along and kick it over. It’s a testament to the isolation and geological stability of the region that when Calendar Circle was discovered in the early 1990s, eight of the standing stones were in their original locations, and another six had just fallen over. In fact, seven millennia of exposure to the natural elements was nothing compared to just a few years of exposure to people. After its discovery, visitors to the site kept adding random stones of their own, so after a few years the powers that be decided it would be safer to remove the stones from their original site altogether and reconstruct the original arrangement in a nearby museum.

Well, I’ve been saying that the structure is about 7 millennia old, but because it’s simply an arrangement of stones, there’s no direct way to date them. But there was a nearby hearth and the organic material in the hearth can be dated using carbon-14 to around 4800 BC.

The circle itself consists of a series of mostly flat stones embedded in the ground. There are eight exceptions, however, eight stones which aren’t flat, but are rather narrow and were placed upright. These come in four pairs, and each pair sits on the opposite side of the circle from another pair. These pairs then form a set of so-called “gates,” or entry points into the circle. Then in the interior of the circle, the line going from one gate to the gate on the opposite side is tracked by a line of pairs of upright rocks. These gates mark two alignments for the structure. Now, because the whole thing is rather small, the alignments are not extremely precise, but one of them traces the north-south axis, and the other is in the direction of sunrise on the summer solstice, or equivalently, sunset on the winter solstice. The way that this probably would have worked is that an individual would stand between the two rocks on the eastern gate at sunrise. When their shadow fell between the rocks on the opposite gate it would be the solstice, or at least around the solstice since there was probably a range of few days when this would happen. In fact, on occasion the Bedouin peoples of northern Africa continue to construct similar kinds of calendar circles to this day and that is way that they use them. The second axis of the Calendar circle, the north-south axis, is somewhat more remarkable because obtaining the direction of north with some precision is, well, maybe not the most difficult task, but at least isn’t completely trivial, particularly since at the time when the Calendar Circle was constructed there was no north star.

Well, about half a kilometer to the west is another structure, named Ring Hill, which is one of the newest structures in the complex, dating to around 3500–3200 BC, so just prior to the first dynasty of Egypt. It’s quite a bit larger than Calendar Circle, about 17 meters in diameter and contains a grave with the skull of a three year old boy. The structure consists of rings of stones, of which the innermost ring is somewhat asymmetric and points towards the east.

The last structure of particular note in Nabta Playa is to me the most remarkable, but of the three structures I’ve talked about it was given the most generic name: Complex Structure A. The builders of this particular monument dug a pit into the ground about two and a half meters deep. There they seem to have discovered a rather large rock made of quartzitic sandstone, about 3 and a half meters by 2 and a half meters in size. The rock probably had a rather flat top to begin with, but the builders went to extra effort to smooth the top of this stone. Then they filled the pit back up with sand, and as they did so, they suspended a second rock above the table rock in the sand. This second rock is known as the “cow stone,” because it was shaped in a way that vaguely resembles a cow, with a projecting bulge that looks like its head. Then, with the cow stone suspended above of the table stone, they completely filled the pit with sand burying both the stones and added several large stones on top above ground. How the builders discovered this particular rock is something of a mystery. They would have had to have gone to some effort to dig deep enough to find it, and the area is not conducive to groundwater, so it’s unlikely that they would have happened to have been digging wells in the area and accidentally stumbled upon it. But this structure seems to have been of some significance for the people who built it not only because of the effort they clearly went to to construct it, but due to its relationship with the surrounding structures. Many of the other megaliths at Nabta Playa were built along three lines that radiate out from this structure. What is rather intriguing about these three radial lines is that they don’t correspond to any of the usual axes we see in megalithic structures like east-west, north-south, or the solstice sunrise and sunsets. However, if the structures were built in the range of 4300–4100 BC, which is consistent with the available evidence, then the first axis lines up with the point on the horizon where the star Arcturus rises, which is the brightest star in the northern hemisphere. The second lines up with the location where the stars of Orion’s belt rise, and the third with the location where Sirius and Alpha Centauri rise, the brightest and third brightest stars in the night sky, respectively.

Well, the ceremonial center at Nabta Playa appears to have been abandoned around the middle of the 4th millennium BC, which, perhaps not coincidentally, is when the desiccation process of the Sahara largely finished and the peoples of the Sahara appear to have moved into more permanent settlements in the Nile river valley, and recorded Egyptian history begins just a few centuries later.

So then, let’s get back to the history of astronomy in Egypt proper. The oldest plausible reference to an astronomer in Egypt is a reference to none other than Imhotep, one of the more remarkable of the earliest Egyptians, all the more so since he wasn’t a pharaoh. Imhotep was a high official of the pharaoh Djoser, of the 3rd dynasty, so he was kicking around very early on in Egyptian history. Over the centuries, Imhotep became revered for his wisdom and acquired something of a mythical status in Egyptian religion, eventually to the point of deification. Now, Imhotep was credited with being wise in matters of astronomy, but these references are a little late and somewhat more dubious, so I can’t really speak too much about his direct influence on Egyptian astronomy. Instead, Imhotep was principally known for his abilities as a physician and architect. Of his abilities as physician the records that survive are purely legendary, but his record as an architect can be seen much more tangibly as he is credited with constructing the first pyramid. Now, up until the time of the Pharaoh Djoser, the pharaohs were entombed in a kind of structure that is today called a “mastaba,” but in ancient Egyptian was called a “per-djet,” which literally translates to “house of eternity.” You might recognize that last part of the word, “djet,” from our last episode, as being one of the ancient Egyptian words for time, with the connotation of a linear, immutable eternity that describes the end of the world.

Well a mastaba is a somewhat simple structure. There were two chambers underground, one of which was the tomb of the late pharaoh, and the other of which contained offerings for the deceased so that he could live in luxury in the afterlife: clothing, jewelry, food, beer, and so forth. Above ground, the tomb was covered with a rectangular slab made of mudbricks, a few meters tall. The main characteristic of the mastaba was that the sides of the mastaba were not vertical, but sloped inwards a little bit.

Imhotep’s main architectural innovation, which then set off a construction frenzy that produced one of Egypt’s principal legacies, was to stack a number of mastabas on top of each other, each somewhat smaller than the last. This transformed the tomb from a rectangular shape, to the first step pyramid in ancient Egypt. After Imhotep, later pharaohs took this design and refined it, or probably more precisely, their unnamed architects took this design and refined it. Although it’s not too hard to see the stacked mastaba structure of Djoser’s pyramid once you know to look for it, after a few generations, the architects ditched this connection to their roots and the pyramids started to be built towards the Platonic ideal of the pyramid shape that we all know and love.

The pyramids are without a doubt the most prominent relic of ancient Egypt in the popular consciousness, so I should probably say a few words about their astronomical connections. Now, one of the things to say about them is that they are very, very old. The Pyramids all date to the beginning of the Old Kingdom. The vast majority of them were constructed during the fourth dynasty, around 2600–2500 BC and by the end of the sixth dynasty pharaohs had essentially stopped constructing pyramids. So although pyramids are the first thing we think of when we think of ancient Egypt, there was actually a only relatively short period of time in Egypt’s long history when they built them.

Part of the reason for their construction being rather short lived in the long sweep of Egyptian history is that they were in some ways victims of their own prominence. The early pyramids at Giza were constructed not too far away from the capital of Memphis where Upper Egypt and Lower Egypt meet, and they are just tremendously large. You really can’t miss them. And, of course, in keeping with ancient Egyptian beliefs about the afterworld, these huge pyramids were stuffed full of unimaginable riches for the dead pharaoh to enjoy in the afterlife, gold, silver, jewels, you name it. So it’s perhaps not all that surprising that right after these enormous monuments were erected and filled up with enormous wealth, they were almost immediately robbed. The pyramids ended up acting as giant flashing neon advertisements telling everyone in the area where all the valuables to steal were. So, in the subsequent 24 dynasties, pharaohs generally preferred to construct their tombs in somewhat more out-of-the-way places and with less prominent exteriors.

Now, the pyramids of ancient Egypt are remarkable for a number of different reasons, but from an astronomical perspective, certainly the most remarkable feature is their alignment. Now, I’ve been talking about various megaliths across Europe and the Sahara for the past couple of episodes, and throughout all this I’ve been remarking on the alignments of these monuments, how they are not randomly oriented, but point in special, astronomically significant directions like east and west, or towards the location of sunrise or sunset on the solstice. But the ancient Egyptian Pyramids take these alignments to an entirely new level. In the case of many of the megaliths I’ve talked about, the alignment is certainly there, but it’s generally not extremely precise. For others it’s not obvious in any individual cases, but can only be seen by looking at the statistical distribution of orientations across many similar megaliths. But in the case of the ancient Egyptian pyramids, these alignments are an order of magnitude better than anything that came before, and, in fact, are better than anything that came after as well for probably more than a millennium. All the pyramids are aligned to the cardinal directions of north-south-east-west to within half a degree, and in most cases, the alignment is much better, averaging between 10 and 15 arcminutes. In the case of the largest pyramid, Khufu’s Pyramid in the Giza complex, the discrepancy with the cardinal directions is a mere 3 arcminutes. To put this in perspective, the base of the pyramid is 230 meters long, so this would mean that the northern corner is only 20 centimeters east of north relative to the southern corner.

So, just how did the builders of these pyramids get them so well aligned? Well, I wish I could tell you, as does every other Egyptologist. But this is perhaps one of the great mysteries in archaeoastronomy. That said, although the techniques of the ancient Egyptians are not known definitively, you won’t be surprised to hear that scholars have ideas. Now, one of the clues that the Egyptians inadvertently left us is in two rather surprising facts about the alignments of the pyramids. The first is that the discrepancies from the true cardinal directions are not random. Instead, the discrepancies are all biased in the same direction, counterclockwise. In other words, if you take a pyramid and stand at its southwestern corner, and look north along the western side, the alignment of this side won’t point exactly to true north, but is slightly to the west of north. And if you then turn to your right and look along the other side, east, this side doesn’t point precisely east, but slightly north of east. And this holds for all of the pyramids. The other, maybe even more surprising fact, is that the alignments actually get worse over time. The oldest pyramids have the best alignments and subsequent pyramids have less accurate alignments. You might expect that as the Egyptians built more pyramids they would have gotten better at it and the alignments would have improved over time as they refined their techniques, but this isn’t so.

What we do know for sure is that there was an apparently important ritual associated with setting the alignment of the Pyramids and laying their foundations, which is known as the “cutting of the cord ceremony.” This was frequently depicted in tombs and shows how the Pharaoh would cut a cord and in so doing would fix the alignment of the pyramid. But, unfortunately for us, although this ritual was often depicted, it was the ancient Egyptian equivalent of a politician donning a hard hat and awkwardly shovelling a bit of ground in front of a bunch of cameras at a formal breaking ground ceremony. How the architects did the actual work to determine the alignment itself before the ceremony was unfortunately not depicted.

One of the theories as to how the Egyptians aligned the pyramids has it that they used the circumpolar stars. The first theory of this kind identifies two stars in particular for this: Kochab and Mizar. Kochab is the second brightest star in Ursa Minor and it’s at the end of the little dipper, and Mizar is in Ursa Major, being the middle star of the handle of the Big Dipper. Incidentally, Mizar is very close to a slightly fainter star called Alcor and in the ancient world these two stars were used as a test of your eyesight. If you could see both Mizar and Alcor, your vision was considered good, and if not, it was bad. In fact, the Japanese took this test a step further and called Alcor Jumyōboshi, or the “longevity star,” because if you couldn’t see it, your eyesight was so bad that you were probably not long for this world. So, the next time you are out at night and see the Big Dipper, check to see if you can find Alcor next to Mizar. Hopefully for your health you can. And, to digress yet a little further, it’s often the case that two stars that are close to each other on the sky have nothing whatsoever to do with each other in real space. One is much further away than the other, but they just happen to line up very close together on our sky. We call these pairs of stars “double stars,” or optical doubles, as opposed to binary stars where the two stars are actually gravitationally bound to each other. Well, as it happens, Mizar and Alcor are in fact a gravitationally bound system. And what’s more, the stars Mizar and Alcor are themselves not individual stars. Mizar is a quadruple star system and Alcor is a binary star system, so the whole thing is actually six stars that are gravitationally bound together. So when you find Mizar and Alcor in the sky, know that you’re actually looking at a sextuple star system.

Well, at any rate, Mizar and Kochab were two stars that the Egyptians may have used to align their Pyramids. At the time, around the middle of the 3rd millennium BC, the north celestial pole was quite a ways away from where it is today due to the precession of the equinoxes. Today we’re rather lucky in that Polaris is a fairly bright star and also fairly close to the pole, so it makes for a good guide on the sky. But at the time that the pyramids were constructed, the closest star to the north celestial pole was Thuban, the brightest star in the constellation Draco. In 2830 BC Thuban actually came quite close to the north celestial pole, being off by only a tenth of a degree. But by the time the pyramids were constructed it was more than a degree away, which means that it couldn’t have been directly used as an alignment to true north since the alignments of the pyramids are better than the alignment of Thuban itself. However, at this time, Mizar and Kochab were on opposite sides of the north celestial pole, and if you drew a line between them, this line came very close to intersecting the pole. So the idea is that the architects would have suspended a plumb bob and then waited until Mizar and Kochab were vertical with the plumb line. By finding the direction where the plumb line covered up both Mizar and Kochab, they would have an alignment to north. One of the nice features of this theory is that as the decades progressed, the precession of the equinoxes would have led to this line between Mizar and Kochab drifting farther and farther from the celestial pole, so the alignments of the pyramids would have gotten worse over time, which is what we observe. And if they had done alignment this in a systematic way, always putting Mizar on top of Kochab, the alignments would have all been biased in one direction, which we also observe. So, the theory has a few nice properties, but it has a couple of problems, too. The first is that one of the earliest pyramids, and the biggest, Khufu’s pyramid, is just too precisely aligned. The pyramid would have had to have been built about a century later than its accepted date of construction for its alignment to be explained by these two stars. Another theory uses two other stars, Phecda and Megrez, both of which are in Ursa Major. These are on the same side of the north celestial pole, but the principle remains the same and the alignment fits better with the construction of Khufu’s pyramid. But a more fundamental problem with both of these theories is that they beg the question of how the Egyptian astronomers determined that these stars were so closely aligned to the north celestial pole in the first place. Somehow they would have had to have some other independent measurement of true north so that they knew that line between Mizar and Kochab or Phecda and Megrez was a good measure of true north. But what method this could have been is unclear.

There are a couple of other possible techniques to measure north generally rely on the position of the sun rather than the nighttime stars. One is fairly straightforward and uses a gnomon, a fancy word for putting a stick in the ground. You watch the shadow the stick casts due the Sun and trace out its path over the course of the day. Then you take a measuring tape and you find pairs of points on opposite sides of the path that are the same distance from the gnomon. Then, draw a line connecting these points and find its midpoint. Finally, you draw a second line from the gnomon to the halfway point and this is the direction of true north. This is a pretty basic technique that doesn’t require a lot of fancy equipment to do, but the main problem is once again the quality of the alignments. It’s hard to do this well enough to get an alignment that is as good as we see with the pyramids. Even if you’re being careful, the Sun itself is an extended disc on the sky, so the shadow it casts is not perfectly sharp. If you use a pinhole you can overcome this issue and get a sufficiently precise alignment, but there’s no evidence that the Egyptians used pinholes for their measurements. Another approach is literally orthogonal to the other approaches. Rather than find the direction of north, you find the direction of east. All you need for this is to find the location of sunrise on the equinox. But once again this just kicks the can down the road, how do you know the date of the equinox? We saw in our tour of Greek astronomy that it wasn’t until quite late that the Greek astronomy had determined the equinox reasonably precisely, and they had to build specialized equipment like an equatorial ring in order to get it, and we have no evidence that the Egyptians built anything like that more than 1000 years earlier. So, the whole thing around the quality of the alignments of the Egyptian pyramids remains something of a mystery. If you can figure it out, well you won’t get a Nobel prize because there’s no prize for the history of Egyptian astronomy, but it would be a pretty cool thing to put on your resume.

Well aside from their remarkable orientations, the Egyptian pyramids have a few other astronomical connections. The first is cosmological and has to do with the fact that they are oriented towards the cardinal directions at all. Not only are the pyramids extremely precisely oriented towards the cardinal directions, they’re also all arranged so that each one has an unobstructed view towards each of the cardinal directions. In order to make this possible, many of them were built along a diagonal line that extends southeast and northwest. For the complex at Giza this is called the Giza diagonal. Of the cardinal directions, north and west had a particular significance. North was the location of the circumpolar stars, which were associated with immortality since they never set. And west was where the Sun set and was the entrance to the Duat, or the underworld. So the Pharaoh’s soul, or ka, in order to attain a happy afterlife, needed to travel first to the west, to enter the Duat, and ultimately to the north, to enter enter the realm of the immortals.

The architects of the pyramids constructed them in such a way as to aid the pharaoh’s ka in this journey. We can see this most clearly in the largest pyramid, called Khufu’s pyramid. Khufu’s pyramid has three main chambers: the King’s chamber, where the Pharaoh was buried; the Queen’s chamber; and the so-called subterranean chamber. The purpose of this last chamber is somewhat unclear. It’s the lowest of the three and it’s possible that it may have originally been intended to be the tomb of the pharaoh, but was abandoned for this purpose for some reason during construction. Astronomically, the most interesting feature was connected to the King’s Chamber. The King’s Chamber has a pair of shafts, one attached to the north wall and the other attached to the south wall. These both extend horizontally a short ways, and then have a bend in them where they start to rise upward at a steep angle, eventually hitting the edge of the pyramid and exposing the shaft to the outside air. When the pyramids were first excavated in the 19th century, the consensus among archaeologists was that these shafts were for ventilation, to bring fresh air into the King’s chamber. But they don’t suit this purpose particularly well. They are long and really quite narrow, about half a square foot in cross section, so they don’t have the capacity to change much air.

What is rather remarkable about these shafts is that they travel north and south with extremely high accuracy — they are about as well aligned as the entire structure itself and I already spent quite some time harping on how extraordinary it is that they managed to achieve such precision in that alignment. To make matters even more interesting, in the 1960s it was realized that the northern shaft rises at an angle of 32 degrees and 36’, and the southern shaft rises at an angle of 44 degrees. This meant that at the time the pyramid was constructed, the northern shaft would have been aligned with the star Thuban, then the north star, as it passed across the meridian at its upper culmination. And the southern shaft was aligned with the star Alnilam as it passed through the meridian, Alnilam being the middle star of Orion’s belt. Now, it’s important to emphasize that Khufu’s pyramid was in no way an observatory — no one was actually going to be able to see these stars through the shaft. That wasn’t the goal, and it wasn’t even possible due to the bends in the shaft. But these two stars weren’t completely random — they held special significance in Egyptian cosmology. Thuban was the closest bright star to the north celestial pole at the time, and as I just mentioned, the region of the northern circumpolar stars was associated with eternity and was where the immortals lived. Thuban, being the northernmost, then, was especially important as a representative of the eternal and unchanging. To the south, the constellation Orion, of which Alnilam would have marked the center, was associated with the god Osiris, who was the god of the afterlife. So the modern belief is that these shafts in the King’s chamber were constructed to aid the Pharaoh’s spirit in journeying toward the appropriate regions of the Duat in his afterlife.

Now, like any theory of the ancient world, this one has its critics. The idea that the shafts were placed there to lead the Pharaoh’s ka to the Duat is well accepted, but the critics maintain that the alignments with any particular stars just comes down to luck. After all, there are a lot of stars on the sky and if you put a shaft at some angle, odds are that it will line up with at least one of them. The other counterpoint that the critics add is that there are also two shafts leading from the Queen’s chamber in addition to the two leading from the King’s chamber, but these two from the Queen’s chamber don’t have any obvious alignments with any particular stars of note in the way that the shafts leading from the King’s Chamber do. To make things more complicated, the shafts leading away from the Queen’s Chamber actually don’t extend all the way out to the exterior of the structure, but just stop partway through in the middle of the pyramid. It’s a little unclear what to make of this information, whether this was intentional, and if so, what the meaning behind it was.

Well, while I’m on the subject of the pyramids I should perhaps say a few words about an idea that has come to be known as the Orion Correlation Theory. If you are of a certain generation you may be familiar with this idea, it garnered some popularity in the media in the 1990s, so if you were watching a lot of TV around that time you might already be familiar with it. It holds that the placement of the three main pyramids of the Giza complex was carefully chosen to mimic the positions of the stars in Orion’s belt. Now, I mentioned already that in order to give each pyramid an unobstructed view of the cardinal directions, the Giza pyramids were placed at a diagonal to each other. But the three pyramids don’t fall exactly along a straight line, there’s a bit of a bend, and they also aren’t equally spaced apart. In the 1980s an author named Robert Bauval noticed that the spacings and angles between these three pyramids matched fairly closely to the three stars of Orion’s belt, which also aren’t precisely in a straight line and also aren’t exactly the same distance from one another. Furthermore, the angle that the stars of Orion’s belt make with respect to north is also very roughly the angle that the Giza diagonal makes with respect to north. But, that’s about all there is to the idea and there’s a few big problems with it. The first is that the angle with respect to north really isn’t all that close when you correct for the precession of the equinoxes. The pyramids are at 38 degrees whereas Orion’s Belt at the time the pyramids were constructed was at closer to 50 degrees. Furthermore, if the pyramids are meant to be a reproduction of the heavens on Earth, there’s another problem which is that you would have to flip it north-south to get the bend to go in the same direction as it does on the sky. The final problem is that there’s just not much more you can say about it. To quote Wolfgang Pauli, it’s an idea that’s not even wrong. There’s really no further evidence that the Egyptians built these particular pyramids with Orion’s Belt in mind. It’s true that Orion had special significance for the Ancient Egyptians, it was the constellation of Osiris, who was the god of the afterlife, but the ancient Egyptians had associations with lots of different stars on the sky. And with only three points, there’s just a very good chance that they will match up with some set of three stars on the sky. If you draw three dots on a piece of paper, odds are that there will be some configuration of three stars that reasonably closely matches the configuration you drew. So, although it’s an idea that captured the popular imagination for a time, it has never been taken seriously by professional Egyptologists. Perhaps the best thing the idea has going for it is that it’s at least less outlandish than the idea that the pyramids were built by space aliens.

Well, I think that this is as good a place as any to pause for this month. Next month I’ll try to wrap up our tour of Egyptian astronomy by looking at a few of the astronomers whose names have survived down to us, along with the instruments they used for their observations. I hope you’ll join me then. Until the next full moon, good night and clear skies.

Additional references

  • Belmonte, Astronomy of Ancient Egypt
  • Clagett Ancient Egyptian Science Vol. 2
  • Magli, Archaeoastronomy
  • Kelly, Exploring Ancient Skies
  • Ruggles, Handbook of Archaeoastronomy