A field with academic work of high quality at one end but uncontrolled speculation bordering on lunacy at the other.

Clive Ruggles - Professor of Archaeoastronomy at the University of Leicester

Archaeoastronomers agree that they study the relationship between people and the sky, but little else. Often they can't even agree on what the name of the subject should be. The problem is that archaeoastronomy can be used to study peoples anywhere in the world from any time in history, including current times. This means that they use all sorts of different evidence and have different opinions about what sort of questions they should be asking. It's most famously associated with the midsummer sunrise alignment at Stonehenge. However there is ongoing debate about how meaningful this alignment is. After all any axis of symmetry has to point somewhere. Proving that an astronomical feature was intentional is a problem, and the best evidence for intent in the British Isles is found across the Irish Sea at Newgrange.

Archaeoastronomical theory: Proving Intent

Newgrange is an Irish Neolithic Passage Tomb. Basically, a large circular mound with a passage cut into it. At sunrise, for around a week either side of the midwinter solstice, the passage is aligned with the rising sun, so that the chamber at the far end of the passage is lit up. It's spectacular, but that isn't enough to prove it was intentional. If it wasn't spectacular then it would be unnoticed like the huge crowds that fail to gather every year on the 19th of May in Solihull. What makes Newgrange special is a feature called the 'light box'.

Above the entrance to the passage at Newgrange is a box which light can shine through. It serves no obvious engineering purpose. It's the wrong shape to be a 'relieving triangle', which would redistribute weight of the earth above as it's cuboid. The only explanation archaeologists have been able to come up with is that it lets light into the tomb, even after the entrance was blocked up. Excavation showed that carved on the stones in this box where strange mysterious symbols. In other cultures these would be interpreted as sun symbols. If the ancient inhabitants of Ireland thought the same then maybe it could tell us something deep and profound about humanity's neurology. Or maybe it's coincidence. Either way this light box is accepted as strong evidence for an interest in astronomy in ancient times.

Unfortunately it's rare to get this kind of evidence at other archaeological sites, so archaeoastronomers have developed methods for finding intention in astronomical activity. Generally they fall into two camps depending on the kind of data they use. In the 1990s and early 2000s it was consider a bit passé to refer to two methods as archaeoastronomers thought they were working towards common ground, but at a recent conference it seemed as though prominent archaeoastronomers were returning to old differences based on the their different interests.¹ In the words of the current president of the International Society for Archaeoastronomy and Astronomy in Culture, Stanislaw Iwaniszewski:

"For a long time I have believed that such diversity requires the invention of some all-embracing theory. I think I was very naïve in thinking that such a thing was ever possible."

Archaeoastronomical theory: Pick a colour

The two methods are referred to as Green Archaeoastronomy and Brown Archaeoastronomy. The names come from a conference held by the International Astronomical Union on archaeoastronomy at Oxford. The participants decided their methods were so different they should be published in two volumes, Archaeoastronomy in the Old World, which had a green cover and Archaeoastronomy in the New World, whose cover was brown. The different methods were largely due to the different sources of data they had access to.

In Europe the focus was on astronomical alignments in prehistoric sites. Alexander Thom's work on Scottish sites was the chief spur for this interest. The primary assertion of this method is that if sites are aligned for astronomical reasons rather than chance, then this should be evidence if you statistically analyse a large enough number of them. This was an approach that mainly appealed to astronomers rather than archaeologists, though one or two archaeologists like Euan MacKie were willing to take the claims seriously. Nonetheless many archaeologists didn't place much value on this approach as it often ignored social questions. Many archaeologists think it's hard to write about people in the past without asking social questions.

In contrast the Americanists had access to a number of ethnographic records especially in Latin America as while the Spanish were just as good at killing natives as other European powers, they also were careful notetakers when it came to recording what they were doing. Additionally there was also local iconography in some places. So for example, when they found a Governor's Palace at Uxmal, Mexico, facing the most southerly rising of Venus over a distant mountain, they weren't too concerned that this could be pure chance, Venus glyphs were visible on the building and Mayan codices had shown Venus was considered an significant object. It's since been suggested that actually the suggested alignment is the wrong way round and that it's the view from the mountain to the the palace that is important, which suggests that historical records might not always be enough to be certain of significance.

In the 1990s it was also suggested there was a 'Blue' Archaeoastronomy, which was another name for Ethnoastronomy. This is the study of relationships between people and the sky in the present. This hasn't really caught on as many Brown archaeoastronomers use ethnographic sources, and the perennial question of when 'current events' become 'history'.

Why Bother?

Despite decades of work, archaeoastronomy is often ignored by archaeologists. This annoys archaeoastronomers and they write papers about it.² Archaeologists for their part have often responded with a 'so what?' Tackling this issue Keith Kintigh said:

I think the principal reason is that archaeologists see archaeoastronomers as answering questions that, from a social scientific standpoint, no one is asking. To put it bluntly, in many cases it doesn't matter much to the progress of anthropology whether a particular archaeoastronomical claim is right or wrong because the information doesn't inform the current interpretive questions. It may be true that a building is lined up within half a degree of true north, but what do I do with that singular fact?

One value of archaeoastronomy is that it can overturn what seem to be common-sense assumptions. A frequent sentence in history of astronomy books is something like: 'Prehistoric man invented the calendar in order to know when to plant his crops.' Authors of such books have clearly never met the Mursi of southwestern Ethiopia.

The Mursi have a calendar which based on twelve lunar months and an extra period at the end of the twelve months, Gamwe, which would be a month if they called it that. Each month or Gamwe is counted from one New moon to the next. Sadly this give a year of twelve or thirteen lunar months and neither properly fits the tropical year. So months of the calendar have to be inserted or dropped. The problem is that no-one will admit to knowing when to insert or drop a year. A meeting they might reckon something, but if you want to meet someone who is claimed to be an expert on the calendar, you'll find he lives miles away and when you get there he'll say that he isn't an expert but knows someone else who is. This person will live miles away again, or else recently died without passing on his expertise. The Mursi calendar therefore works by argument, but it doesn't really matter because they don't use it to plant crops. Instead they watch the flooding of the local river, because it's a bit pointless planting if the land hasn't been inundated. Whatever they're used for, calendars are not for agriculture.

Another use for archaeoastronomy is as an ethnic or religious tag. If you're excavating a burial ground and find the burials face north-south, then it's a safe bet you're not dealing with a Christian society. A project in Sicily has found the Carthaginian colonists embedded solar alignments into their infrastructure by the alignment major urban roads towards specific sunrises. Greek colonists preferred to align superstructure, such as temples towards the rising sun. As yet the natives, who were squashed between the two settling powers have not been associated with a distinctive astronomical preference.

Archaeoastronomy can also help explain the timing of events. Cycles of warfare between Mayan states appear to have been regulated by the appearance of Venus, leading some archaeologists to refer to these events as 'Star Wars'. Inca festivals are said to have occurred on specific days associated with sunrises over ceques, conceptual lines radiating out from the centre of their empire. In Europe, the Oracle of Delphi could originally only be consulted on one day of the year. However the ancient Greek cities each kept their own calendar and started the year at different times. Hence they wouldn't agree what day of the year it was. It has been shown that consultation of Apollo Delphinios, was connected to the appearance of the Greek constellation Delphinios, these days known as Delphinus.

...but is it astronomy and is it archaeo?

Further Reading