Astronomical Heritage

What is the Astronomical Heritage?

Astronomical Heritage is evidence relating to the practice of astronomy and to social uses and representations of astronomy. It exists in the form of the tangible remains of monuments, sites and landscapes with a link to the skies that constitute a well-defined physical property. It can also involve movable objects such as instruments and archives, intangible knowledge, including indigenous knowledge still preserved today, and natural environments that support human interest in astronomy, e.g. through the cultural use of their horizons or dark night skies.

Image: a view of the Stonehenge Neolithic site in Wiltshire county, England.
Copyright: David Ball (www.davidball.net), source: Wikimedia Commons.

Credits
the contents of this article are based upon text in the ICOMOS–IAU Thematic Study
Original text © Clive Ruggles, Michel Cotte and the contributing authors
Source: UNESCO Astronomy and World Heritage Webportal, www2.astronomicalheritage.net

Astronomy in context

Practices related to astronomy are inextricably linked to broader assemblages of cultural activities. As a result, the material heritage of astronomy in the form of artefacts and constructions is often deeply integrated within material heritage of a broader nature and significance. This is equally true whether or not the astronomy in question constitutes modern ‘rational’ science. The pre-Columbian metallurgical centre at Viña del Cerro in Chile, for instance, provides an excellent example of astronomy in a broader, integrated context of resource exploitation, sacred places, calendar and landscape. This implies that we should not focus exclusively upon ‘astronomical heritage sites’ per se but pay due attention to sites exhibiting an important set of valuable attributes, astronomy being just one component among others. An excellent example in this regard combining outstanding scientific and architectural qualities is the Einstein Tower in Potsdam, Germany, an astrophysical observatory and also a masterpiece of the history of German architecture, designed by Erich Mendelsohn (1857–1953) and built in the 1920s.

Image: the Einstein Tower (1924), an astrophysical observatory and a masterpiece of the German architecture. Copyright: R. Arlt. Source: www2.astronomicalheritage.net

Ulugh Beg’s observatory in Samarkand, Uzbekistan, is an example of the mutual reinforcement of value coming from different cultural fields - urban, social and political history, history of architecture and decoration, cultural practices in the arts, etc. - in Central Asia during the 15th century. The immediate urban surroundings of the 18th-century Jantar Mantar observatory in Jaipur, India, inscribed onto the World Heritage List in 2010, provide another example where overlapping aspects of value are gathered together in one property; similarly, Dengfeng Observatory in China, also inscribed in 2010, forms part of a large site including a range of 13 temples, towers, a monastery, and gardens.

Astronomy can take many forms but it is never alone: it is always a part of a larger ensemble of attributes that characterise a human society in its particular geographical and historical context.

The heritage of astronomy is often linked to complex systems of representation. For example, astronomical observations are frequently motivated by a need to predict the future (for various reasons including prognostication, predicting recurrent phenomena, or ‘testing’ hypotheses in modern ‘rational’ context), and this leads to the development and use of a variety of forms of symbolic notation. As a result, attempting to interpret the heritage involves examining the diverse relationships that exist between human beings and the sky as manifested through the use of artefacts and representations. These not only include notations and drawings but also architectural constructions and urban planning that ‘symbolise’ the skies in various ways: terrestrial material manifestations of the human cognisance of the universe that can be seen as a concretisation of the human relationship with the heavens. We must also be concerned with protocols and methods of observation, together with a full range of beliefs and modes of behaviour (i.e. magic as well as science, astrology as well as astronomy in the modern rational sense, and religious faiths as well as beliefs in physical laws).

This raises the issue of the meaning of the term ‘science’, both as simple terminology and as a more complex epistemological question. One can envisage, effectively, a straightforward dichotomy between modern ‘rational’ methods of enquiry (narrow definition of science) and any attempt to comprehend the nature of the perceived life-world by imposing some sort of cognitive structure upon it (wide definition). However, at a more subtle level the question of what constitutes ‘pure science’ in astronomy remains extremely open and dependent upon context. It is certainly allied to the question of predicting the future and it is also linked with cosmology (in the anthropological sense) and with religion and ideology. The general question of what constitutes ‘pure’ science or ‘pure’ astronomy is relevant in so far as it helps to define modes of connection between astronomical beliefs and practice and their social and cultural context and hence leads to more efficient ways of understanding the value of heritage sites with a relationship to astronomy.

Categories of Astronomical Heritage

The interplay between the tangible and the intangible is an inherent and fundamental aspect of astronomical heritage, as indeed it is of science heritage in general. The same is also true, to some degree, of all properties on the World Heritage List.

 

Image: the main categories in which the astronomical heritage is usually classified and their interrelations. Copyright and source: www2.astronomicalheritage.net

 

In heritage terms, we can identify three main aspects of the ‘astronomical system’ associated with a given place and thus contributing to the value of a site:

  • material evidence of the astronomical place in the form of fixed property and/or movable objects;
  • the results of scientific activities (in the broadest sense), including but not restricted to astronomical observations;
  • socio-cultural applications and uses of astronomy at a given moment or over a given period for the site.

Each of these three main categories gives rise to both tangible evidence and intangible heritage. Following the World Heritage Convention, the tangible evidence must be divided into two subcategories: movable heritage and immovable heritage. Immovable heritage is central to the application of the Convention but movable heritage is not, strictly speaking, covered by the Convention. (The term ‘immovable’ is used in a juridical sense, to mean something that has not been globally displaced from its position in the soil, in other words something that has permanent links with the architectural framework of its construction or of its natural foundation. In this sense, it actually means ‘fixed in its original position’ or ‘not moved [yet]’, and for this reason we generally use the term 'fixed' to describe this type of heritage. On the other hand, ‘movable’ has its common-sense meaning).
Thus, for example:

 

 

Tangible immovable heritage

Tangible movable heritage

Intangible heritage

Property / objects

Architecture; permanent constructions and structures, fixed instruments

Plans; movable artefacts; movable instruments

Practical/technical expertise; rules of use and maintenance; structural/ architectural history of the site

Results of scientific activities (in the broadest sense)

Stone carvings; wall paintings; iconography; palaeography; symbolic representations

Records/accounts of observations; printed and digital data; sky maps; scientific publications

Knowledge and understanding; calculations and theories

Socio-cultural applications and uses

Astronomically aligned architecture; light-and-shadow hierophanies; urban planning and landscapes constructed using astronomy

Archives; drawings; maps and plans, tools or instruments using astronomical properties (for example, sextants for maritime purposes or movable sundials in social use)

Calendars; ideology; predictions of the future (whether rational or irrational from modern perspectives)


While incomplete and begging many issues, such as the imprecise boundaries between certain types of evidence, the table suffices to highlight the important question of the relationships between material evidence, as the main focus of the application of the World Heritage Convention at the present time, and intangible heritage, as evidence for the value of material manifestations. Within the tangible category, we must also examine the relationships between fixed (immovable) and movable objects: again, only the first of the two is currently relevant to the World Heritage Convention.

Some examples

The various categories of astronomical heritage, ‘tangible immovable’, ‘tangible movable’, and ‘intangible’, are interrelated in different ways in different contexts. Despite the fact that the World Heritage Convention focuses on tangible immovable heritage, the essential evidence for certain types of early astronomy is almost exclusively in the other forms.


Image: detail of the main surviving fragment of the Antikythera mechanism, a bronze mechanical device dating to the later 2nd century BC and containing at least 30 hand-driven gearwheels, that calculated and displayed a range of astronomical cycles. Copyright: Antikythera Mechanism Research Project. Source: www2.astronomicalheritage.net


Our knowledge of astronomy in ancient Mesopotamia, for example, comes exclusively from movable cuneiform tablets, together with its intangible legacy in the astronomy of other cultures. In other cases, different forms of heritage may tend to relate to different aspects of the astronomy. The classic example of this is ancient Greece, where the historical documents relate mainly to the development of mathematical astronomy by an elite of scholars, while much of the material astronomical heritage (e.g. the configuration of ancient temples) relates to astronomy in the service of religion practiced by the people at large. Since the first of these forms a crucial part of the history of modern scientific astronomy, the archaeoastronomical evidence is largely ignored by historians of astronomy. However, it is no less important from a cultural astronomy (anthropological) perspective. Indeed, while a classical heritage approach focused on the fixed heritage could redress the balance, it might well overemphasize the latter.

Islamic astronomy presents another balance between the availability and state of conservation of tangible fixed evidence and other forms of heritage relating to crucial developments in astronomy. Based on the available historical sources, we can create quite an accurate account of several aspects of the development of astronomy in the Islamic world during the 12th to 16th centuries, and we know that it provided a vital link between ancient Greek astronomy and the subsequent development of scientific astronomy in renaissance Europe and in Mogul India. However, despite the huge importance of the Islamic observatories in the development of mathematical and observational astronomy during this period, none has survived intact. In other words, the fixed heritage that not only bears witness to but fundamentally underpinned these developments has largely disappeared. In this context, the partial survival of two major observatories (Maragha and Samarqand) that demonstrably played a very significant role in these developments is all the more fortunate. This must surely influence our assessment of their very high value as astronomical heritage, an importance that could come into play, for example, when facing authenticity and integrity concerns.

The tangible fixed Astronomy heritage: monuments & sites

Monuments, sites and cultural landscapes relating to astronomy stand as a tribute to the complexity and diversity of ways in which people rationalized the cosmos and framed their actions in accordance with that understanding. Such material testimonies of astronomy, found in all geographical regions, span all periods from prehistory to the present day. The close and continual interaction between astronomical knowledge and its role within human culture is a vital element of the value of these properties.


Image: Pulkovo observatory, Russian Federation, detail. Copyright: Vladimir Ivanov. Source: Wikimedia Commons.

The following may be identified as the principal types of tangible fixed astronomical heritage:

  • Observatories as ‘scientific monuments’. The architectural approach that is standard when considering the value of a heritage site may only form a limited part of the assessment of a scientific site.
  • Fixed instruments.
  • Material representations of the results of astronomical observations and cognitive understanding:
  • Tangible representations of observations, events and predictions (calendars, time measurements, predictions of eclipses, zodiacs, celestial representations, etc);
  • Cosmological and symbolic representations (iconography, palaeography).
  • The material products of the application of astronomy: constructions, architecture and urbanism related to applied astronomy and/or bearing astronomical information.
  • Properties whose design and/or landscape setting have significance in relation to celestial objects or events.
  • Cultural landscapes related to the history of astronomy and/or human cultural practices related to astronomy.


The 'instruments' and 'material representations' bring in to focus the tricky question of the borderline between fixed property and movable artefacts. Material representations in the form, for example, of rock art are fixed; those in the form of paper records are movable. An instrument in the form of a fixed ‘monument’ could serve exactly the same purpose as a personal portable instrument or a ‘semi-movable’ instrument located in specific places for observation. A historical observatory may have movable domes or floors; an interferometer may have a fixed disc together with movable ones. This issue is not peculiar to astronomy but applies to science and technology heritage in general.

The tangible movable heritage of Astronomy: instruments & artefacts

The distinction between fixed property and movable objects is important from the juridical and heritage perspective, but has no real significance for astronomers. For an instrument, what is important is its scientific function and its technical performance. The distinction between a fixed instrument and a movable instrument is only a question of factors such as dimension, technology and materials, precision of observation, stability, and the necessity of moving the instrument for observation. A more pertinent distinction is that between a ‘collective instrument’, shared by a professional group of astronomers, and an individual instrument. The notion of the personal use of astronomical instruments - for example, not only for scientific research but also for navigation, leisure purposes, etc.; or not only for astronomical observations but also for decoration, collection, etc - could easily be linked with the broader application and/or social use of astronomy, but only more rarely with a decisive improvement in observational techniques and/or theoretical progress that might mark it out as having exceptional universal value.

Image: Edwin Aldrin about to set foot on the moon. Photograph by Neil Armstrong. Source: NASA public domain.

A collection of rare or unique movable instruments authentically associated with the history of an observatory is obviously a major part of the latter’s heritage value. Thus, assessing an observatory must therefore involve making a detailed study of the functionality and of the construction and use of each instrument, exactly as would be necessary for a movable part of a technological monument or for a ‘machine-tool’ in industrial heritage. For the scientist, this is the real core of the material value of the observatory, perhaps more than walls and architecture; these could in a really poor state while the site remains of major importance in the history of astronomy.

Concerning collections of movable instruments, the UNESCO initiative ‘Movable Heritage and Museums’ may be relevant to some aspects of this type of heritage.

Some issues

Assessing the value of tangible movable heritage can raise a variety of issues. For example, in the case of Palaeolithic mobile art on movable artefacts—objects such as the Ishango Bone from the Democratic Republic of the Congo that may provide some of the earliest insights into human perceptions and uses of the skies:

  • Does their existence strengthen the value of their place of discovery, even if they are now removed from it in museum collections?
  • Should we focus at all on the place of discovery, when what is important from the astronomical heritage point of view is the object itself?
  • Is the authenticity of the object more to do with the reliability of the archaeological context it came from than with its own ‘genuineness’ (e.g. lack of damage/restoration)?

Jumping from one end of the timescale to the other, space heritage throws the issue of ‘fixed’ versus ‘movable’ heritage into sharp focus. A ‘fixed’ location on the moon, such as Neil Armstrong’s landing site or first footprint, is a moving point relative to any location on the earth; while a geostationary satellite which, to some degree of approximation, is stationary relative to any location on the earth, would not seriously be considered a ‘fixed’ object. Clearly, relativity of movement seems a poor criterion for heritage evaluation in these cases (albeit an excellent illustration for a major concept of modern physics). The only reasonable conclusion is that the dichotomy between ‘fixed’ and ‘movable’ makes little sense as a classificatory criterion in astronomical heritage in particular, or in science or technology heritage in general.

The intangible heritage of Astronomy: knowledge & ideas

The ‘core’ heritage of astronomy as ‘science’ in either the broad or narrow sense - in other words, ideas, knowledge and understanding - is intangible. Tangible and intangible heritage are inextricably interwoven, both in modern contexts and in the past, stretching back into prehistory.

Image: the Milky Way, on the right the first radio map at 160 MHz by G. Reber, Astrophysical Journal 100 (1944), while on the left a recent 1400 MHz map by W. Reich. Copyright: Max Planck Institut. Source: www2.astronomicalheritage.net.

All of the thematic essays illustrate this in different ways. For example, the historical development of radio astronomy provides an excellent example of continual interaction of these different categories of legacy in a modern context. The issue is also highly pertinent in the case of indigenous uses of astronomy, an example being the Mursi calendar, an Ethiopian indigenous calendar of huge importance from the point of view of the anthropology of astronomy since it undermines a number of assumptions people tend to make about the ‘inevitable’ ways in which calendars developed in the past. It may sometimes be possible to recognise surviving astronomical or calendrical practices as part of a living ‘cultural landscape’ such as the Cliff of Bandiagara (Land of the Dogons) World Heritage Site in Mali.

The main goal of the World Heritage Convention is not to celebrate the achievements of individuals, even if it sometimes recognises the exceptional value of their material productions in context (e.g. the fortifications of Vauban in France and the works of Antoni Gaudí in Spain). Of course, individual scientific genius has played a crucial role in the development of modern Western science, but this aspect of the heritage of astronomy - however crucial it might seem to today’s astronomers and scientists - remains a limited and recent one in the broad cultural perspective of the WH Convention. Hence, as at the twin-monastery of Wearmouth–Jarrow, United Kingdom, the fact that a place is associated with a great person (in this case, Bede of Jarrow) and/or their discoveries does not constitute value by itself, although it can clearly strengthen other aspects of the value.

Archives & Documents: links between tangible and intangible scientific heritage

The scientific corpus that represents this core heritage of astronomy comprises the material sources of the history of astronomy: its archives and documents, in the broadest sense. An item of this type could be a tangible drawing or engraving on a monument or a palaeographic inscription, but it is frequently a ‘movable legacy’ such as a written document, map or printed matter. The recording and transmission of information has certainly been a crucial issue throughout the history of astronomy. It is manifested in cave art, papyri, cuneiform tablets, paper-books of observations, paper archives, books and ephemerides, photos in visible and non-visible wavelengths, spectra, and digital databases. Obviously, a major part of the evidence for the development of ideas in astronomy exists in the form of movable documentation contained in archives, collections and bibliographies. Such documentation provides material support for the recording of observational results, prediction, calculation, theory, the use of astronomy, etc. These documents are the product of scientific activities in their cultural context. 

Image: Jean Picard's "Le Traité du Nivellement (1684)" with the triangulation method to determine one degree of arc of the Paris meridian. Source: public domain. 

The core of scientific knowledge is mainly intangible. It is an intellectual framework of the human spirit using specialised languages (written language, mathematics, etc) and images (drawings, maps, photographs, physical information such as spectra, and so on).

Archaeoastronomical and astronomical documentation is mainly related to:

  • records of observations and events, tables of observations;
  • physical images and information (photos, spectra, radio maps, etc);
  • interpretation and theories (physical laws of the universe), cosmology (global theories and interpretations of the sky and universe);
  • calculations and predictions (ephemerides, calendars, astronomical interpretations and predictions);
  • social uses of astronomy, whether or not rational in modern scientific terms (calendars, navigation, agricultural practices related to the moon, astrology);
  • symbolism, faith and religious uses of astronomy; and
  • art and decoration.

In fact, the production and retention of archives could be considered the very heart of the scientific productivity of a laboratory or observatory. They are movable underpinnings for collections of data emanating from sky observations, calculations, predictions and theoretical interpretations. It is in this way that the ‘intangible property’ represented by archives in a broader sense is most directly linked with the scientific activities and reputation of the ‘astronomical property’.

Natural heritage relating to Astronomy: landscape and sky

Certain natural environments are intimately connected with cultural interests in astronomy, and bear witness to such activities throughout the ages. This applies to the visible landscape where, for example, points on the natural horizon mark the observed rising and setting points of celestial bodies. But it is particularly true of the dark night sky itself, which can preserve links with the perceived cosmos that have existed since time immemorial.

Image: the Pnyx hill in Athens (Greece) with Meton's observatory foundations (copyright and source: About Athens).

The Pnyx is a place significant for the history of astronomy because historical records attest that it was the place from which the Greek astronomer Meton made observations of the solstice in the 5th century BC that led to his discovery of the calendrical cycle now known as the ‘Metonic cycle’. There are no tangible remains, fixed or movable, bearing direct witness to Meton’s observations. However, Meton’s observations may well have made use of the visible horizon (formed by a hill 3km away). In this sense, the natural landscape formed part of the ‘instrument’ and so directly forms part of the astronomical significance of the place.

The same is true of the many prehistoric and historical constructions aligned, for example, on the horizon rising or setting positions of the sun, such as Stonehenge in the United Kingdom or the seven-stone antas of Portugal and Spain, the appropriate horizon point being marked in some cases by a natural feature such as a distant hill-slope or mountain summit (as at Atituiti Ruga, Mangareva, French Polynesia). It would be misleading to view most of these constructions as observing ‘instruments’, since that was not their main function, but it is true to say that the alignment - the feature that ‘connects’ the human monument to the sky and contributes to (or in some cases, constitutes the totality of our knowledge of) its significance in relation to astronomy - links the human construct and the surrounding natural landscape - doing so in an even more specific way when a horizon ‘foresight’ completes the alignment. It follows that the natural landscape, and in some cases specific features within it, must in a very real sense be considered as contributing to the value of the monument, implying, for example, that Management Systems should address to question of keeping the natural landscape intact and the sightline unobstructed. At the same time, natural sites used for astronomical purposes (both in the present and in the past, where there is clear evidence to support the assertion) could form elements of ‘cultural landscapes’.

A related issue is the removal of a monument, even for its own protection, as at Abu Simbel or, potentially, at Nabta Playa in Egypt. If the monument contains connections with the surrounding landscape, such as alignments, then its removal may have stronger implications than simply transforming it from fixed to movable heritage, since such connections will be destroyed, thus also removing an important (and perhaps the only) aspect of its value as astronomical heritage and thus destroying its integrity.

Human constructions incorporating astronomical alignments are also, of course, ‘connected’ in a cognitive sense to the astronomical body in question: this connection was periodically ‘revealed’ - reaffirmed visually - when the sun, star, etc actually rose or set in the alignment. Light-and-shadow ‘hierophanies’, as at the Pantheon in ancient Rome or the Baptistery of Parma in medieval Italy, represent another instance where a direct connection between a human construction and a celestial body is periodically ‘made physical’. It is also true that in a more general sense all astronomical heritage sites have a connection to the very sky to which they related.

Given that an important aspect of the heritage of many ancient and historical sites is the observation of certain naked-eye astronomical phenomena, the possibility of actually observing those phenomena today is a relevant consideration in valuing and preserving that heritage. Since many sites relate to night-time observations, a consideration of obvious importance in this respect is the visibility of the dark night sky. In this sense, a dark sky is an aspect of the quality of the natural environment of a cultural site. in terms of scientific value (and cultural value in general) connected with the history of astronomy, it is quite valid to recognise the absence of light (pollution) as a prerequisite for the satisfactory observation of the night sky.

Dark sky places

In dark night sky areas, the ability to see natural starlight preserves the visual links to the sky that have connected humankind to the cosmos throughout history. There has been increasing recognition in recent years of the crucial importance of maintaining dark skies in various places around the world, and the Starlight Initiative has worked since 2007 to find ways to recognise and protect such heritage, for example developing the concept of a Starlight Reserve. However, neither Starlight Reserves nor Dark Sky Parks can be recognized by the World Heritage Committee as specific types or categories of World Heritage cultural and natural properties since no criteria exist for considering them under the World Heritage Convention. Unquestionably, the sky itself, the dark night sky, celestial objects, and starlight as such cannot be nominated to the World Heritage List within the framework of the Convention.


Image: the imposing shape of the emu (the largest bird native to Australia and ratite relative of the African ostrich) in the sky known to Australian Aboriginals, above a probable rock art depiction of it (copyright: Barnaby Norris. Source: http://www.atnf.csiro.au).


Nonetheless, in the ICOMOS–IAU Thematic Study it is recognized that dark skies relate strongly to other aspects of the heritage of astronomy, and the study highlights various ways in which dark skies and light pollution issues can be highlighted in nomination dossiers for potential World Heritage sites. A way forward for those seeking to have such sites recognized and protected under the World Heritage Convention might be to explore the ways in which the dark skies associated with a site or landscape are intertwined with other aspects of astronomical heritage that could conceivably be recognized as of outstanding universal value. Such issues are explored in detail among the case studies and discussions on this web portal.

These questions are also linked to one of particular interest to professional astronomers: how can we protect dark skies at the world’s major optical observatories that are vital for cutting-edge astronomical research? For this reason, three such observatories - Mauna Kea observatory in Hawai‘i, the AURA observatory in Chile and the Canarian observatories in Spain - are all included as case studies within the Thematic Study and on this portal.

Why to preserve the Astronomical Heritage?

The sky is our common and universal heritage, and forms an integral part of the total environment that is perceived by humankind. Heritage that bears witness to people’s interpretation and understanding of the sky from earliest times through to the present day stands as a record of the extraordinary diversity of ways in which our species has viewed, interpreted and understood the relationship between itself and the world—the universe—that we inhabit.

Including the interpretation of the sky as a theme in World Heritage is a logical step towards taking into consideration the relationship between mankind and its environment. It follows that it is important within the World Heritage Convention to recognize and safeguard cultural sites and natural landscapes that encapsulate and epitomize the relationship between humankind and the sky.

Astronomical heritage does not only come in the form of fixed, tangible heritage (sites and landscapes). It is equally important to recognize and protect movable objects and artefacts, the intangible heritage of astronomy in various forms, and natural heritage relating to astronomy—including the visibility of the dark night sky itself.

Image: the Pyramids of Giza, Egypt, detail (copyright and source: Clive Ruggles, www.cliveruggles.net).

about the Author, Clive Ruggles

Clive Ruggles (born 1952) is a British astronomer, archaeologist and academic regarded as one of the leading figures in the field of archaeoastronomy, having authored several works on the subject. Clive Ruggles is Emeritus Professor of Archaeoastronomy in the School of Archaeology and Ancient History at the University of Leicester, England. He also holds the posts of President of the Prehistoric Society, President of the International Astronomical Union (IAU) Commission for the History of Astronomy, and is the Chair for the IAU World Heritage and Astronomy Working Group. Clive Ruggles, the former President of the International Society for Archaeoastronomy and Astronomy in Culture, has worked in many parts of the world and published numerous books, papers and articles on subjects ranging from prehistoric Europe and pre-Columbian America to indigenous astronomies in Africa and worldwide. He has ongoing fieldwork projects in Peru and Polynesia, and is also a key figure in the IUA-UNESCO joint initiative to promote and preserve the astronomical heritage sites.


Image: Professor Clive Ruggles (copyright and source: University of Leicester, https://www2.le.ac.uk/).

To get more information and materials please visit Clive Ruggles' official website: http://www.cliveruggles.net/

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Credits & Navigation

Images and texts are copyrighted Clive Ruggles, whenever not otherwise specified. Source: UNESCO Portal to the Heritage of the Astronomy.

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