**Antonio César González-García 1,\* and Juan Antonio Belmonte <sup>2</sup>**


Received: 8 March 2019; Accepted: 10 April 2019; Published: 14 April 2019

**Abstract:** If astronomy can be understood as the contemplation of the sky for any given purpose, we must realize that possibly all societies throughout time and in all regions have watched the sky. The why, who, how and when of such investigation is the pursuit of cultural astronomy. When the research is done with the archaeological remains of a given society, the part of cultural astronomy that deals with them is archaeoastronomy. This interdisciplinary field employs non-invasive techniques that mix methodologies of the natural sciences with the epistemology of humanities. Those techniques are reviewed here, providing an excellent example of sustainable research. In particular, we include novel research on the Bohí Valley Romanesque churches. The results provided go beyond the data. This is because they add new value to existing heritage or discovers new heritage due to the possible relationship to the spatial and temporal organization of past societies. For the case of the Bohí churches the results point to a number of peculiarities of these churches in a valley in the Pyrenees. This links these aspects to the ritual, practical and power sphere of past societies. A wonderful example of such links is the high mountain sanctuaries in Gran Canaria, where archaeoastronomy helps promoting a World Heritage candidacy.

**Keywords:** cultural astronomy; archaeoastronomy; field techniques; Bohí Romanesque churches; Canary Islands; landscape archaeology

#### **1. Introduction**

Far from being a particular version of the history of astronomy, or a specialized archaeometry, cultural astronomy is something else. Human knowledge can be specialized (i.e., medical, astronomical, etc.) but when such knowledge is used it becomes social and human, as society is the context where all that is human is produced and used. This is why we must ask for the sense of such uses. When we do this with respect to specialized knowledge, there appear research questions, data and methodologies that go beyond the expertise of the specialist on such knowledge. A social and human version of this knowledge is thus needed to answer those questions. In the case of the sky, such an approach is cultural astronomy.

There is one part of the humanities that focuses on the environment influence on human societies. However, there is only one discipline that deals with the relationship between those societies throughout history and the sky below they dwell, and this is what has been called astronomy in culture or rather cultural astronomy.

If a naïve and simple definition of astronomy could be sky-watching, then cultural astronomy is realizing that any society, present or past, has actually looked at the sky. This is why as astronomers we would like to know what they were watching. However, as cultural astronomers we want to understand how they generated, processed and used such knowledge. Hence, the focus is not in the celestial objects they identified but how those were understood and incorporated by that society from their cultural point of view.

Cultural astronomy thus tries to answer questions that go beyond astrophysical interest. It tries to understand how astronomical knowledge is generated in ancient, traditional and ancestral societies. How is such knowledge transmitted? What are the processes of social production, transference and diffusion of such astronomical knowledge? Was it invented by all societies independently? Or, on the contrary, were some basic principles (like the identification of solstices or equinoxes) generated in some cultures and later transmitted to others? Were 'primitive astronomers' some kind of 'artisans', i.e., a specific social group? Were they privileged? Or, was the astronomical lore simply produced in a general sense, without any concrete author? Other pertinent questions, such as what was the influence of the concept of the sky in the power relations or the structuration of society may also arise.

In a definition given by Stanislaw Iwaniszewski [1], cultural astronomy is the study of the relations between people's perception of the sky and the organization of different aspects of the social life. Such study, according to Edwin Krupp [2] includes several different topics: Calendars, practical observation, celestial cults and myths, symbolic representation of astronomical events, naming celestial objects, astronomical concepts or laws, the astronomical orientation of tombs, temples, sanctuaries and towns, traditional cosmology and the ceremonial use of astronomical traditions.

Cultural astronomy thus includes several other sub-disciplines, such as ethnoastronomy and astronomy in traditional and subsidiary societies (like pastoral groups, etc.), or archaeoastronomy. In this context, archaeoastronomy can be understood as the study of the orientation of buildings and their possible relationship to astronomical events. In short then, archaeoastronomy is the study of cultural astronomy through the material record, while ethnoastronomy would be the study of cultural astronomy via the ethnography of present day or past societies.

Cultural astronomy is a relatively new discipline that complements and deepens, from different points of view, the understanding of several other disciplinary fields. As examples to be considered we may count on: Landscape archaeology, understood in a broad sense, including the construction of spatial materiality in relation to the observation of astronomical phenomena [3]; the history of religions, from the orientation of sacred sites to the ritual conditioning of calendars; historic anthropology, understood as a holistic focus on human actions in the past, where cultural astronomy contributes by studying the different images of the cosmos in different societies. Finally, it could also be seen as a history of science as it studies the knowledge of the universe in different cultures and historical periods.

As with any other historical or archaeological data, archaeoastronomy pretends to shed light into the people in the past, and to do so we must do it by approaching the way of thinking of the society we deal with [4]. This means that the data and hypotheses advanced by cultural astronomy have to be supported on and by the archaeological, ethnographic or historical record [5].

In summary, cultural astronomy offers an increase in the understanding of cultural and archaeological heritage in two ways: It discovers 'new heritage' and provides new value to that already known or helps identifying heritage at risk (see Figure 1).

All in all, it should be noted that cultural astronomy is the way to get in contact with a basic heritage element: The one constituted by the materials, knowledge and values related to the observation of the sky. Cultural astronomy offers a way to gain access to a number of phenomena that otherwise would pass unnoticed. UNESCO has recognized such dimension in the category of Astronomical World Heritage Sites [6,7]. In the subsequent sections of the present paper we will focus on the sustainability of archaeoastronomical research. First we will present how this research is currently done, next we will introduce the results for a particular case study and, finally, we will focus on a qualitative example on how this research helps promoting a candidacy for a World Heritage Site.

**Figure 1.** Archaeoastronomical fieldwork helps identify heritage at risk. This was the case with the Dahmiyeh dolmen field, one of the Bronze Age megalithic necropolises in Jordan studied by the authors [8]. These megalithic monuments of the local Bronze Age are built with a valuable travertine stone and were located next to the site where this material was obtained. A stone quarry now menaces this dolmen field and several dolmens are already being dismantled without compassion. © A.C. González-García.

#### **2. Sustainability of Archaeoastronomical Research**

According to Nature's website [9], sustainability is the ability to endure, for example, by exploiting resources in a way that does not deplete their availability for the future. We will use this definition as a working tool for the next paragraphs when presenting how archaeoastronomy does research and if this is done in a sustainable way. In other words, in such a way that may allow further data acquisition from the same site in the future. A final consideration on another aspect of the sustainability of archaeoastronomical research will be done at the conclusion section.

As indicated above, archaeoastronomy is done through the study of the archaeological record from the perspective of cultural astronomy. It is common lore that the conventional archaeological methodology is non-sustainable as it relies on the excavation and thus on the 'destruction' of the archaeological site. However, it is indeed true that nowadays there are a number of non-invasive techniques helping archaeology, such as different kinds of geophysical surveys, and some of them will be acknowledged and mentioned later on.

From this perspective, and having in mind the sustainability of research in archaeoastronomy, there are different levels open for consideration. For example, do we need excavation for doing research in archaeoastronomy? Are there any alternatives?

All these issues deal with the methodology employed to carryout data acquisition. In general, archaeoastronomical data are obtained through the visual inspection of the site of interest. Once a line of sight is defined for whatever reason (notably a symmetry line of a given building or the alignment of a number of artificial elements) our measuring device is situated either on top of that line of sight or closely parallel to it. Then two readings are usually recorded, the angle of this line with respect to true north (the azimuth) and the altitude of the horizon along that line of sight. Those two measurements together with the location of the observation point read through a GPS will facilitate the translation of these readings into astronomical measurements (see Figure 2; for a complete and detailed description of the measurement procedure see [10]).

**Figure 2.** The data acquisition process in archaeoastronomy does not involve any kind of disturbance to the archaeological or heritage sites. The picture shows a common procedure for the measurement of a built structure, in this case a Romanesque church in Galicia, Spain. The technique involves deriving a parallel line to the wall to be measured with two rods. © A.C. González-García.

One other kind of data acquisition is done through the landscape inspection and measurement for the verification of potential landscape/heavenly relations. This is done by carefully inspecting the horizon observed from a particular site. There, singular directions, perhaps marked by other sites located at the horizon or by natural singular features such as notches or mountain peaks, could be linked to directions where interesting astronomical phenomena can be observed (see e.g., [11–13]).

In order to verify if the astronomical data is of any use at any archaeological site, one must be very careful. The pertinence of such data ought to be reckoned, making questions such as: Were astronomy or astral deities known to be important for the society we are dealing with? (see e.g., [14–17]). If we do not have any such information, as for prehistoric societies, either we can rely on solid interpretations of the iconography or we can try to proof the intentionality by performing statistical studies that may indicate the existence of orientation patterns that could only be explained by astronomical phenomena (see e.g., [18,19]).

As we can see, there is no need for an excavation or any other invasive technique within this procedure, so in principle the methodology per se is quite non-interventionist, nor harmful and thus sustainable. Another question is that to be able to define the measured line or the observation point we may need previously excavated structures, or not, if new techniques such as geo-radar are applied.

One key issue that we advocate archaeologists should incorporate to their excavation/prospection routine, as a standard procedure, is that of a horizon reconstruction or recording, which is seldom altered during the excavation process. This procedure can be as easy as taking a number of photographs, normally more than eight, to cover the 360◦ visible from the prospection or excavation site. This would help the researcher to reconstruct the horizon in the laboratory, for instance using customary image treatment software, and then incorporating such landscape into planetarium software, such

as Stellarium [20]. This will be useful to verify if there are interesting and/or important astronomical connections from that site. As we have argued, this does not necessarily take much time and the amount of data that can be provided is substantial (see Figure 3).

**Figure 3.** With the help of a panoramic picture properly referenced we can reconstruct the sky viewed in ancient times. The picture shows a panoramic reconstruction from the newly discovered cultic platform in Petra (Jordan) that has been incorporated into Stellarium to replicate the sky appearance at the epoch of use. © A.C. González-García.

Another way to do this landscape reconstruction implies having a good geo-referenced positioning of the site and employing geographic information systems (GIS) to reconstruct the horizon. This is useful not only for those cases when a 360◦ photograph of the site is not available, but also for those where vegetation or buildings hamper the visibility of the sites. These can incorporate for instance data from LiDar flights. Indeed, the resolution of the digital terrain model (DTM) is the main problem to solve as it will dictate the uncertainty in the potential astronomical links of the sites investigated (see [12] for a recent use of this technique).

Of course, a kind of data that can be used is that derived from Geo-Radar and other geo-physical explorations of potential sites. In this case, the data can also be put into context of the landscape inspection and then derive orientation measurements and potential astronomical connections to those sites. One example of this kind of research has been carried out with a series of the circular enclosures in southern Portugal [21].

Finally, we should not forget the data acquisition techniques where we can take into account the 3D reconstruction of built structures. Those can then be incorporated into DTMs and planetarium models to investigate, verify and discover potential astronomical relations of light and shadow effects ([13,22,23], see Figure 4).

One key issue with the sustainability of data acquisition is the replicability of the research. This implies taking care of performing reliable estimates for our data (including errors), and a comprehensive description of the methodology employed and the sites measured.

One fundamental question we must carry out from this enumeration, regarding the sustainability of this kind of research, is that as the methodology does not imply altering the sites, this kind of measurements can be performed without (much) impact to already existing heritage sites. Besides it

provides new data that normally have not been taken into account before and thus complements and expands our understanding of these sites and helps to bring new heritage into knowledge.

**Figure 4.** A 3D reconstruction of the dolmen of Dombate (A Coruña, Spain). Top: The 3D rendering has been included within a digital terrain model into the Stellarium software allowing investigation of the illumination of the paintings inside the megalithic chamber today precluded by the preservation measures of the dolmen. Bottom: The backstone of the dolmen, possibly the first to be erected at the time of construction, displays an elaborate program of decoration with sophisticated geometric forms, which are directly illuminated by the first sunbeams of the winter solstice. The 3D reconstruction allows verifying that the illuminated part never reaches further up than the area with red paintings. © A.C. González-García.

Nowadays, there is a rather well established methodology that shows that this discipline can be fully incorporated into the humanities as a useful tool to understand human past. In parallel there is an on-going substantial effort to upgrade the methodology by incorporating new techniques as well as new epistemological discourses.

In this sense, cultural astronomy studies in general and in particular those of archaeoastronomy are closely connected to the spatial and landscape dimension. Such connection links archaeoastronomy to the social aspect of the landscape. Thus, space is socially and culturally built. A number of variegated disciplines highlight that a 'landscape' is a created reality by social action. This can be found in different social disciplines such as human geography [24,25], anthropology [26–29], archaeology [30,31] and the history of religions [32–34].

From this point of view, archaeoastronomy is a key element for understanding and complementing our knowledge on the social construction of space and, given the recurrent and cyclical nature of the astronomical events, also the time and temporal dimension of these landscapes.

In a recent paper, Kristiansen [35] argues that while the objectivist ideal of procesualism has been long time set aside, it is also evident that the subjectivist version of post-procesualism or the hermeneutic liberalism are not the solution either. The enhancement of critic reflexivity as a central component of all theories and practices, and the consolidation of a weak or soft model of science (with rigorous data, robust methodologies and reflexive theories: R3 science), paves the way to new proposals that Kristiansen exemplifies with his "new paradigm" for archaeology.

His proposal combines the science-based potential of the archaeological investigation (big data, profound archaeometries, information sciences and visualization techniques) with solid theories to produce significant narratives, as a way to merge the point of view of anthropology, and humanities in general, with that of the 'hard' sciences.

In our understanding, cultural astronomy, given the characteristics presented above, is well positioned to face such integration also taking care of the sustainability of the research. The use of massive empirical datasets, together with the use of innovative visualization techniques (like 3D modeling of buildings inserted in a planetarium software) integrated in more solid theories, allow constructing narratives that provide an integrative and holistic sense to the social study of the sky.

In the following pages we will show how such an endeavor can be exemplified in one case study, the group of Romanesque Churches of the valley of Bohí (Lleida, Spain). Finally, we will present how this endeavor can help in the promotion of heritage sites, taking the high mountain sanctuaries and complexes in the central part of the island of Gran Canaria as an example.
