Stonehenge: Solar calendar or not?
Last year, Timothy Darvill's paper made the headlines: Stonehenge could have been used as a solar calendar.
It seemed to make a lot of sense. After all, solsticial alignments and calendars go together, like cheese and biscuits, and Stonehenge is famous for its solsticial alignments. Indeed, Darvill suggested the calendar was kept in time by observing the summer sunrise or winter solstice (or both). This is the way it was supposed to work;
If we consider only the large megaliths of the 'Stage 2' construction, circa 2620-2480 BCE, then...
1. There are apparently 30 upright stone megaliths in the outer Sarsen ring. Although many are missing now. there is archaeological evidence for all of them. These can obviously be used to count the days of each 30-day month.
2. Do this 12 times and you get 360 days.
3. The final 5 'epagomenal' days can be counted with the trilithon horseshoe pillars (using 1 day for each pair of upright monoliths). This gives a total of 365 days, or a solar year.
4. A leap year of 366 days every 4th year can be counted using the 4 station stones. This kept the calendar in time with the seasons, pretty well.
This seems like a an elegant explanation for many of Stonehenge's features, considering that making a calendar is a natural extension of observing the solstices. But there was a problem; the number 12 was missing. So, how would ancient people have counted the proper number of months in a year? How would they know when to add the extra 5 or 6 epagomenal days at the end of the year?
Darvill had a solution for this too. They could simply observe the midwinter sunset or midsummer sunrise, along which Stonehenge's axis is oriented. When the solstice was approaching, instead of adding another month of 30 days they could add 5 or 6 epagomenal days signalling the end of the year. Simples.
A nice solution.
However, just in the last day or so, a rebuttal to Darvill's idea has been published, also in the journal Antiquity, by Magli and Belmonte (2023). They argue that Darvill's idea is his own invention, and Stonehenge was never used this way by the people who built it. In fact, their words are pretty harsh, and they offer a warning that this kind of research should be left to the experts (i.e. them). Ouch!
So, who's right? Darvill or Magli and Belmonte? And what should we think of Magli and Belmonte's warning? Well, this is my take on it.
At the outset, I should say that I consider Darvill's proposal very reasonable. It makes a lot of sense, although it's not completely satisfactory. Unfortunately, the numerical correlation is not very strong, at all, partly because the number '12' does not appear anywhere at Stonehenge. Nevertheless, given how calendars and solsticial observations go hand-in-hand, I think it has a reasonable chance of being right. Certainly, it's worth publishing in a journal. I'm glad I know about it, even if it's quite speculative.
So why are Magil and Belmonte so apparently outraged at the proposal? What exactly is their beef? They list 3 major problems, as they see it, with Darvill's proposal that they label 'numerology', 'archaeoastonomy' and 'cultural', and then they finish with their warning.
Let's have a look at each argument in turn.
A. Numerology
Magli and Belmonte somewhat condescendingly label this kind of idea 'numerology'. By this, they effectively mean pseudo-science. Yikes! That's gotta hurt.
In their view, explaining the correlation between Stonehenge's pillars and a calendar is in the same ball-park as other whacko 'numerological' ideas, like how aliens constructed the moon to be the same apparent size as the sun, or similar.
Of course, this is nonsense. Magli and Belmonte seem to misunderstand the entire basis of the scientific method. The whole point of science (see my previous post) is the efficient explanation of observations or correlations. In this sense, Darvill's idea can be considered scientific, since it is a fairly efficient explanation for Stonehenge's design.
To better understand why Darvill's idea is scientific and not numerological, we need to understand the difference between these processes. Put simply, numerology is almost the same as science. They both attempt to explain apparent correlations. However, we call some ideas 'numerological ' for two key reasons;
1. They have no real statistical support, due to cherry-picking or bias for example, i.e. they pick out a random peak in some noise and call it a signal. In other words, the strength of the signal is very low to zero.
2. They propose mechanisms that are currently completely unacceptable to science, such as aliens built the moon, or where there can obviously be no causal mechanism.
Either one of these reasons is enough to label an idea 'numerological'. Of course, saying that an idea is contrary to accepted science is not really a good reason, since scientific paradigms can change. But, some numerological proposals are so whacko, its hard to conceive of science ever changing enough to accommodate them. If both of these reasons are in play, there really is no chance for the idea. It's as dead as a dodo.
Clearly, Darvill's proposal is nowhere near having either of these problems. In fact, it is so obviously a reasonable idea, that Magli and Belmonte's objection to it on this basis actually undermines their whole rebuttal. We can question their objectivity. Clearly, the numbers 30, 12, 5 and 4 can be used to construct a solar calendar with leap years, and their appearance together is sufficiently unusual that this constitutes a fairly strong signal. However, Stonehenge's signal is weakened by the missing number 12. On the other hand, this weak signal is amplified by Stonehenge's solsticial alignment, since then we are primed to look for a calendar in advance and the number 12 is no longer needed. Finding these numbers with a solsticial alignment so readily at Stonehenge therefore makes a reasonably good case. On the other hand, I don't like that we have to count each trilithon pillar as half a day, and we have to ignore the heel stone (not shown above). Therefore, I think Darvill's proposal should be considered as quite reasonable, but far from conclusive.
Magli and Belmonte also claim that in 30 years of research they have never found any calendar system in association with any 'major monument' for pre-scientific societies. But of course, this is a self-fulfilling prophesy. If they discount all such potential calendar systems in terms of numerology, it follows they will never find one.
Ultimately, Magli and Belmonte' numerological compliant is itself unscientific, because it misunderstands the scientific method. In fact, it smells of hypocrisy, since if you read some of Belmonte's previous papers, on identifying the Egyptian Decans for example, you will see some good examples of highly speculative research. But, it seems, Belmonte is not happy for others to speculate as he has done.
B. Archaeoastronomy
Magli and Belmonte claim, essentially, in this section of their rebuttal that Stonehenge's solsticial alignment could not be used to construct a calendar with a leap year. Are they right?
Of course not. In fact, it would be easy. The length of a solar year can be measured accurately by observing the equinoxes, and less accurately by observing the solstices due to the solar standstill effect. Nevertheless, over a period of, say, 50 years it is easy to calculate with good precision the number of days in a year. Stonehenge or its precursor monuments could have been used to do this. In fact, anyone could have done this far back into the Palaeolithic era. This knowledge could have been quite widely dispersed.
Okay, maybe a single experiment over a 50 year period is a little adventurous at this time. Instead, consider the following trial-and-error method. Let's suppose we know a solar year is slightly more than 365 days. This will easily be seen by the rapid drift in the summer solstice relative to a 365 day calendar. After 40 years of a 365 day calendar your calendar will be about 10 days out, meaning the summer solstice will be about 10 days late. This drift is easily noticed and was known as the Sothic cycle in ancient Egypt. So, lets add a leap day every other year. Doing this, you will find the drift is equally rapid in the other direction. Clearly we are adding twice as many days per year as is necessary. Therefore, let's interpolate and add a leap year every 4th year. You will find this works really very well, as a solar year is very nearly 365.25 days.
So, whether we measure the length of a year over a suitably long interval, or we use trial-and-error over several generations, a solar calendar with a leap year every 4th year is easily found, especially if you already have a giant monument with solsticial alignments. We can therefore reject Magli and Belmonte's argument. Indeed, it's surprising they even mentioned this.
C. Cultural
Magli and Belmonte' argument here seems to be based on some inherent superiority of the Egyptian astronomers. They seem to imply that if the Egyptian's did not use a leap-year system until the Roman era, then it is impossible that the early Briton's could have done so. I don't see any good reason to think this. As explained above, it would be easy.
However, Darvill did compare Stonehenge's apparent 365.25 day calendar with the Egyptian civic calendar (which does not have a leap year) of 365 days, which is obviously incorrect. Nevertheless, this error is trivial and does not affect any of Darvill's conclusions.
In fact there are many ways Stonehenge's builders could have acquired knowledge of a 365.25 day solar year. They could have easily worked it out for themselves, as explained above. Or, they could have acquired this knowledge from Egypt or anywhere else for that matter. But Magli and Belmonte complain that contact between Briton and Egypt is almost completely unknown at this time, and in any case the Egyptians used a 365-day civil calendar, not one with a leap year. But this misses the point. The Egyptians knew their civic calendar drifted and therefore they would have known how to correct it, if they wanted. They obviously didn't feel it was necessary at that early time in the 3rd millennium BCE. Moreover, there must have been plenty of people travelling around who could have communicated this knowledge from somewhere else, Egypt or otherwise. Magli and Belmonte's argument is that evidence is lacking for this. To my mind, this places far too much trust in the completeness of the archaeological record. We have barely scratched the surface of Briton with archaeological digs. Its far too early to rule out any contact with Egypt. And as I already indicated, other places could have known of this cycle, or the Britons could easily have worked it out for themselves.
In fact, considering that these Neolithic Britons circa 2500 BCE are descended in large part from Anatolia's farmers (this is known from DNA studies), and we already have strong evidence from Gobekli Tepe of keen naked-eye astronomy in the Palaeolithic era in Anatolia and Europe, I suspect this kind of cultural knowledge was widespread.
I therefore think we can reject all of Magli and Belmonte's main criticisms of Darvill's work. Certainly, I am glad he published his idea.
But what about Magli and Belmonte's final warning. Here it is in full...
"Archaeoastronomy has endured decades of difficult development in order to become the respected scientific discipline that it is today (see e.g. Aveni 2008;Magli 2020; Boutsikas et al. 2021). We believe that matters such as ancient calendars, astronomical alignments and cultural astronomy should be reserved to specialists, trained in the subject, and not left to researchers from other disciplines, however renowned and knowledgeable in their own fields. Multidisciplinarity and collaboration offer the most effective way forward."
This final paragraph of their rebuttal is more than just nonsense, it is unethical. It is a logical fallacy known as an 'appeal to authority'. It has no place in academic debate, and it should not have been published. It is effectively a kind of ad-hominem. It says that, because 'you' are not an expert like 'us' that you cannot make any useful contribution. Such ad-hominem attacks are proscribed in academic debate. After all, who decides who is an expert and who is not? No, in academic debate, all that matters is the evidence and arguments. Everything else is a distraction.
Indeed, this kind of 'authority' argument is characteristic of religion, not science. Magli and Belmote are quite right that archaeoastronomy has a tarnished past. But their appeal to authority only serves to maintain this, and its publication in a learned journal amplifies the problem.
By the way, Darvill has responded in a newspaper that Magli and Belmonte's rebuttal is just a 'rant' by some committed Egyptologists. I tend to agree.
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