
Archaeoastronomy (also spelled archeoastronomy) is the
interdisciplinary
Interdisciplinarity or interdisciplinary studies involves the combination of multiple academic disciplines into one activity (e.g., a research project). It draws knowledge from several other fields like sociology, anthropology, psychology, ec ...
or multidisciplinary study of how people in the past "have understood the
phenomena
A phenomenon ( : phenomena) is an observable event. The term came into its modern philosophical usage through Immanuel Kant, who contrasted it with the noumenon, which ''cannot'' be directly observed. Kant was heavily influenced by Gottfried ...
in the
sky, how they used these phenomena and what role the sky played in their
culture
Culture () is an umbrella term which encompasses the social behavior, institutions, and norms found in human societies, as well as the knowledge, beliefs, arts, laws, customs, capabilities, and habits of the individuals in these grou ...
s".
Clive Ruggles
Clive L. N. Ruggles (born 1952) is a British astronomer, archaeologist and academic. He is the author of academic and popular works on the subject. In 1999, he was appointed professor of archaeoastronomy at the School of Archaeology and Ancient His ...
argues it is misleading to consider archaeoastronomy to be the study of ancient
astronomy
Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
, as modern astronomy is a scientific discipline, while archaeoastronomy considers symbolically rich cultural interpretations of phenomena in the sky by other cultures. It is often twinned with ''ethnoastronomy'', the
anthropological study of skywatching in contemporary societies. Archaeoastronomy is also closely associated with
historical astronomy
Historical astronomy is the science of analysing historic astronomical data. The American Astronomical Society (AAS), established 1899, states that its Historical Astronomy Division "...shall exist for the purpose of advancing interest in topics re ...
, the use of historical records of heavenly events to answer astronomical problems and the
history of astronomy
Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, cosmological, calendrical, and astrological beliefs and practices of prehistory: vestiges of these are still found i ...
, which uses written records to evaluate past astronomical practice.

Archaeoastronomy uses a variety of methods to uncover evidence of past practices including archaeology, anthropology, astronomy, statistics and probability, and history. Because these methods are diverse and use data from such different sources, integrating them into a coherent argument has been a long-term difficulty for archaeoastronomers. Archaeoastronomy fills complementary niches in
landscape archaeology and
cognitive archaeology. Material evidence and its connection to the sky can reveal how a wider landscape can be integrated into
beliefs about the cycles of nature, such as
Mayan astronomy
Maya astronomy is the study of the Moon, planets, Milky Way, Sun, and astronomical phenomena by the Precolumbian Maya Civilization of Mesoamerica.
The Classic Maya in particular developed some of the most accurate pre-telescope astronomy in the ...
and its relationship with agriculture. Other examples which have brought together ideas of cognition and landscape include studies of the cosmic order embedded in the roads of settlements.
Archaeoastronomy can be applied to all cultures and all time periods. The meanings of the sky vary from culture to culture; nevertheless there are scientific methods which can be applied across cultures when examining ancient beliefs. It is perhaps the need to balance the social and scientific aspects of archaeoastronomy which led Clive Ruggles to describe it as "a field with academic work of high quality at one end but uncontrolled speculation bordering on lunacy at the other".
History
Two hundred years before
John Michell
John Michell (; 25 December 1724 – 21 April 1793) was an English natural philosopher and clergyman who provided pioneering insights into a wide range of scientific fields including astronomy, geology, optics, and gravitation. Considered "o ...
wrote the above, there were no archaeoastronomers and there were no
professional archaeologists, but there were astronomers and
antiquarians
An antiquarian or antiquary () is an aficionado or student of antiquities or things of the past. More specifically, the term is used for those who study history with particular attention to ancient artifacts, archaeological and historic sit ...
. Some of their works are considered precursors of archaeoastronomy; antiquarians interpreted the astronomical orientation of the ruins that dotted the English countryside as
William Stukeley
William Stukeley (7 November 1687 – 3 March 1765) was an English antiquarian, physician and Anglican clergyman. A significant influence on the later development of archaeology, he pioneered the scholarly investigation of the prehistor ...
did of
Stonehenge
Stonehenge is a prehistoric monument on Salisbury Plain in Wiltshire, England, west of Amesbury. It consists of an outer ring of vertical sarsen standing stones, each around high, wide, and weighing around 25 tons, topped by connecting ...
in 1740, while
John Aubrey
John Aubrey (12 March 1626 – 7 June 1697) was an English antiquarian, antiquary, Natural philosophy, natural philosopher and writer. He is perhaps best known as the author of the ''Brief Lives'', his collection of short biographical pieces. ...
in 1678 and
Henry Chauncy
Sir Henry Chauncy (12 April 1632 – April 1719) was an English lawyer, topographer and antiquarian. He is best known for his county history of Hertfordshire, published in 1700.
Life
He was born in Ardeley (then known as Yardley), Hertfordshir ...
in 1700 sought similar astronomical principles underlying the orientation of churches. Late in the nineteenth century astronomers such as
Richard Proctor and
Charles Piazzi Smyth investigated the astronomical orientations of
the pyramids.
The term ''archaeoastronomy'' was advanced by Elizabeth Chesley Baity (following the suggestion of Euan MacKie) in 1973, but as a topic of study it may be much older, depending on how archaeoastronomy is defined. Clive Ruggles says that
Heinrich Nissen, working in the mid-nineteenth century was arguably the first archaeoastronomer. Rolf Sinclair says that
Norman Lockyer, working in the late 19th and early 20th centuries, could be called the 'father of archaeoastronomy'. Euan MacKie would place the origin even later, stating: "...the genesis and modern flowering of archaeoastronomy must surely lie in the work of
Alexander Thom in Britain between the 1930s and the 1970s".
In the 1960s the work of the engineer Alexander Thom and that of the astronomer
Gerald Hawkins, who proposed that
Stonehenge
Stonehenge is a prehistoric monument on Salisbury Plain in Wiltshire, England, west of Amesbury. It consists of an outer ring of vertical sarsen standing stones, each around high, wide, and weighing around 25 tons, topped by connecting ...
was a
Neolithic
The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several part ...
computer, inspired new interest in the astronomical features of ancient sites. The claims of Hawkins were largely dismissed, but this was not the case for Alexander Thom's work, whose survey results of
megalith
A megalith is a large stone that has been used to construct a prehistoric structure or monument, either alone or together with other stones. There are over 35,000 in Europe alone, located widely from Sweden to the Mediterranean sea.
The ...
ic sites hypothesized widespread practice of accurate astronomy in the British Isles. Euan MacKie, recognizing that Thom's theories needed to be tested, excavated at the
Kintraw
Alexander Thom (26 March 1894 – 7 November 1985) was a Scottish engineer most famous for his theory of the Megalithic yard, categorisation of stone circles and his studies of Stonehenge and other archaeological sites.
Life and work Early ...
standing stone site in Argyllshire in 1970 and 1971 to check whether the latter's prediction of an observation platform on the hill slope above the stone was correct. There was an artificial platform there and this apparent verification of Thom's long alignment hypothesis (Kintraw was diagnosed as an accurate
winter solstice
The winter solstice, also called the hibernal solstice, occurs when either of Earth's poles reaches its maximum tilt away from the Sun. This happens twice yearly, once in each hemisphere (Northern and Southern). For that hemisphere, the winte ...
site) led him to check Thom's geometrical theories at the Cultoon
stone circle
A stone circle is a ring of standing stones. Most are found in Northwestern Europe – especially in Britain, Ireland, and Brittany – and typically date from the Late Neolithic and Early Bronze Age, with most being built from 3000 BC. The ...
in Islay, also with a positive result. MacKie therefore broadly accepted Thom's conclusions and published new prehistories of Britain.
[MacKie 1977] In contrast a re-evaluation of Thom's fieldwork by Clive Ruggles argued that Thom's claims of high accuracy astronomy were not fully supported by the evidence. Nevertheless, Thom's legacy remains strong,
Edwin C. Krupp
Edwin Charles Krupp (born November 18, 1944) is an American astronomer, researcher, author, and popularizer of science. He is an internationally recognized expert in the field of archaeoastronomy, the study of how ancient cultures viewed the sky ...
wrote in 1979, "Almost singlehandedly he has established the standards for archaeo-astronomical fieldwork and interpretation, and his amazing results have stirred controversy during the last three decades." His influence endures and practice of statistical testing of data remains one of the methods of archaeoastronomy.

The approach in the
New World
The term ''New World'' is often used to mean the majority of Earth's Western Hemisphere, specifically the Americas."America." ''The Oxford Companion to the English Language'' (). McArthur, Tom, ed., 1992. New York: Oxford University Press, p. ...
, where anthropologists began to consider more fully the role of astronomy in
Amerindian
The Indigenous peoples of the Americas are the inhabitants of the Americas before the arrival of the European settlers in the 15th century, and the ethnic groups who now identify themselves with those peoples.
Many Indigenous peoples of the A ...
civilizations, was markedly different. They had access to sources that the
prehistory
Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use ...
of Europe lacks such as
ethnographies[Zeilik 1985][Zeilik 1986] and the historical records of the early
colonizers. Following the pioneering example of Anthony Aveni, this allowed New World archaeoastronomers to make claims for motives which in the Old World would have been mere speculation. The concentration on historical data led to some claims of high accuracy that were comparatively weak when compared to the statistically led investigations in Europe.
This came to a head at a meeting sponsored by the
International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...
(IAU) in
Oxford
Oxford () is a city in England. It is the county town and only city of Oxfordshire. In 2020, its population was estimated at 151,584. It is north-west of London, south-east of Birmingham and north-east of Bristol. The city is home to the Un ...
in 1981. The methodologies and research questions of the participants were considered so different that the conference proceedings were published as two volumes. Nevertheless, the conference was considered a success in bringing researchers together and Oxford conferences have continued every four or five years at locations around the world. The subsequent conferences have resulted in a move to more interdisciplinary approaches with researchers aiming to combine the contextuality of archaeological research, which broadly describes the state of archaeoastronomy today, rather than merely establishing the existence of ancient astronomies, archaeoastronomers seek to explain why people would have an interest in the night sky.
Relations to other disciplines
Archaeoastronomy has long been seen as an interdisciplinary field that uses written and unwritten evidence to study the astronomies of other cultures. As such, it can be seen as connecting other disciplinary approaches for investigating ancient astronomy: astroarchaeology (an obsolete term for studies that draw astronomical information from the alignments of ancient architecture and landscapes),
history of astronomy
Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, cosmological, calendrical, and astrological beliefs and practices of prehistory: vestiges of these are still found i ...
(which deals primarily with the written textual evidence), and ethnoastronomy (which draws on the ethnohistorical record and contemporary ethnographic studies).
Reflecting Archaeoastronomy's development as an interdisciplinary subject, research in the field is conducted by investigators trained in a wide range of disciplines. Authors of recent doctoral dissertations have described their work as concerned with the fields of archaeology and cultural anthropology; with various fields of history including the history of specific regions and periods, the history of science and the history of religion; and with the relation of astronomy to art, literature and religion. Only rarely did they describe their work as astronomical, and then only as a secondary category.
Both practicing archaeoastronomers and observers of the discipline approach it from different perspectives. Other researchers relate archaeoastronomy to the history of science, either as it relates to a culture's observations of nature and the conceptual framework they devised to impose an order on those observations or as it relates to the political motives which drove particular historical actors to deploy certain astronomical concepts or techniques. Art historian Richard Poss took a more flexible approach, maintaining that the astronomical rock art of the North American Southwest should be read employing "the hermeneutic traditions of western art history and art criticism" Astronomers, however, raise different questions, seeking to provide their students with identifiable
precursors
Precursor or Precursors may refer to:
* Precursor (religion), a forerunner, predecessor
** The Precursor, John the Baptist
Science and technology
* Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of un ...
of their discipline, and are especially concerned with the important question of how to confirm that specific sites are, indeed, intentionally astronomical.
The reactions of professional archaeologists to archaeoastronomy have been decidedly mixed. Some expressed incomprehension or even hostility, varying from a rejection by the archaeological mainstream of what they saw as an archaeoastronomical fringe to an incomprehension between the cultural focus of archaeologists and the quantitative focus of early archaeoastronomers. Yet archaeologists have increasingly come to incorporate many of the insights from archaeoastronomy into archaeology textbooks and, as mentioned above, some students wrote archaeology dissertations on archaeoastronomical topics.
Since archaeoastronomers disagree so widely on the characterization of the discipline, they even dispute its name. All three major international scholarly associations relate archaeoastronomy to the study of culture, using the term ''Astronomy in Culture'' or a translation. Michael Hoskin sees an important part of the discipline as fact-collecting, rather than theorizing, and proposed to label this aspect of the discipline ''Archaeotopography.'' Ruggles and Saunders proposed ''Cultural Astronomy'' as a unifying term for the various methods of studying folk astronomies. Others have argued that astronomy is an inaccurate term, what are being studied are
cosmologies and people who object to the use of
logos
''Logos'' (, ; grc, λόγος, lógos, lit=word, discourse, or reason) is a term used in Western philosophy, psychology and rhetoric and refers to the appeal to reason that relies on logic or reason, inductive and deductive reasoning. Aristo ...
have suggested adopting the Spanish ''cosmovisión''.
When debates polarise between techniques, the methods are often referred to by a colour code, based on the colours of the bindings of the two volumes from the first Oxford Conference, where the approaches were first distinguished.
[Aveni 1986] Green (
Old World
The "Old World" is a term for Afro-Eurasia that originated in Europe , after Europeans became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia, which were previously thought of by th ...
) archaeoastronomers rely heavily on statistics and are sometimes accused of missing the cultural context of what is a social practice. Brown (
New World
The term ''New World'' is often used to mean the majority of Earth's Western Hemisphere, specifically the Americas."America." ''The Oxford Companion to the English Language'' (). McArthur, Tom, ed., 1992. New York: Oxford University Press, p. ...
) archaeoastronomers in contrast have abundant ethnographic and historical evidence and have been described as 'cavalier' on matters of measurement and statistical analysis. Finding a way to integrate various approaches has been a subject of much discussion since the early 1990s.
Methodology
There is no one way to do archaeoastronomy. The divisions between archaeoastronomers tend not to be between the physical scientists and the social scientists. Instead, it tends to depend on the location and/or kind of data available to the researcher. In the Old World, there is little data but the sites themselves; in the New World, the sites were supplemented by ethnographic and historic data. The effects of the isolated development of archaeoastronomy in different places can still often be seen in research today. Research methods can be classified as falling into one of two approaches, though more recent projects often use techniques from both categories.
Green archaeoastronomy
Green archaeoastronomy is named after the cover of the book ''Archaeoastronomy in the Old World''. It is based primarily on statistics and is particularly apt for prehistoric sites where the social evidence is relatively scant compared to the historic period. The basic methods were developed by Alexander Thom during his extensive surveys of British megalithic sites.
Thom wished to examine whether or not prehistoric peoples used high-accuracy astronomy. He believed that by using horizon astronomy, observers could make estimates of dates in the year to a specific day. The observation required finding a place where on a specific date the Sun set into a notch on the horizon. A common theme is a mountain that blocked the Sun, but on the right day would allow the tiniest fraction to re-emerge on the other side for a '
double sunset'. The animation below shows two sunsets at a
hypothetical site, one the day before the
summer solstice and one at the summer solstice, which has a double sunset.
To test this idea he surveyed hundreds of stone rows and circles. Any individual alignment could indicate a direction by chance, but he planned to show that together the distribution of alignments was non-random, showing that there was an astronomical intent to the orientation of at least some of the alignments. His results indicated the existence of eight, sixteen, or perhaps even thirty-two approximately equal divisions of the year. The two
solstice
A solstice is an event that occurs when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around June 21 and December 21. In many count ...
s, the two
equinox
A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears zenith, directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" ...
es and four
cross-quarter days, days halfway between a solstice and the equinox were associated with the medieval Celtic calendar. While not all these conclusions have been accepted, it has had an enduring influence on archaeoastronomy, especially in Europe.
Euan MacKie has supported Thom's analysis, to which he added an archaeological context by comparing
Neolithic Britain to the
Mayan civilization
The Maya civilization () of the Mesoamerican people is known by its ancient temples and glyphs. Its Maya script is the most sophisticated and highly developed writing system in the pre-Columbian Americas. It is also noted for its art, arc ...
to argue for a stratified society in this period.
To test his ideas he conducted a couple of excavations at proposed prehistoric observatories in Scotland.
Kintraw
Alexander Thom (26 March 1894 – 7 November 1985) was a Scottish engineer most famous for his theory of the Megalithic yard, categorisation of stone circles and his studies of Stonehenge and other archaeological sites.
Life and work Early ...
is a site notable for its four-meter high standing stone. Thom proposed that this was a foresight to a point on the distant horizon between Beinn Shianaidh and Beinn o'Chaolias on
Jura. This, Thom argued, was a notch on the horizon where a double sunset would occur at midwinter. However, from ground level, this sunset would be obscured by a ridge in the landscape, and the viewer would need to be raised by two meters: another observation platform was needed. This was identified across a gorge where a platform was formed from small stones. The lack of artifacts caused concern for some archaeologists and the petrofabric analysis was inconclusive, but further research at
Maes Howe
Maeshowe (or Maes Howe; non, Orkhaugr) is a Neolithic chambered cairn and passage grave situated on Mainland Orkney, Scotland. It was probably built around . In the archaeology of Scotland, it gives its name to the Maeshowe type of chambered c ...
[MacKie 1997] and on the
Bush Barrow Lozenge led MacKie to conclude that while the term 'science' may be anachronistic, Thom was broadly correct upon the subject of high-accuracy alignments.
In contrast
Clive Ruggles
Clive L. N. Ruggles (born 1952) is a British astronomer, archaeologist and academic. He is the author of academic and popular works on the subject. In 1999, he was appointed professor of archaeoastronomy at the School of Archaeology and Ancient His ...
has argued that there are problems with the selection of data in Thom's surveys. Others have noted that the accuracy of horizon astronomy is limited by variations in
refraction
In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomen ...
near the horizon. A deeper criticism of Green archaeoastronomy is that while it can answer ''whether'' there was likely to be an interest in astronomy in past times, its lack of a social element means that it struggles to answer ''why'' people would be interested, which makes it of limited use to people asking questions about the society of the past. Keith Kintigh wrote: "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." Nonetheless, the study of alignments remains a staple of archaeoastronomical research, especially in Europe.
Brown archaeoastronomy
In contrast to the largely alignment-oriented statistically led methods of green archaeoastronomy, brown archaeoastronomy has been identified as being closer to the
history of astronomy
Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, cosmological, calendrical, and astrological beliefs and practices of prehistory: vestiges of these are still found i ...
or to
cultural history
Cultural history combines the approaches of anthropology and history to examine popular cultural traditions and cultural interpretations of historical experience. It examines the records and narrative descriptions of past matter, encompassing the ...
, insofar as it draws on historical and ethnographic records to enrich its understanding of early astronomies and their relations to calendars and ritual.
The many records of native customs and beliefs made by Spanish chroniclers and ethnographic researchers means that brown archaeoastronomy is often associated with studies of astronomy in the Americas.
One famous site where historical records have been used to interpret sites is
Chichen Itza
Chichen Itza , es, Chichén Itzá , often with the emphasis reversed in English to ; from yua, Chiʼchʼèen Ìitshaʼ () "at the mouth of the well of the Itza people" was a large pre-Columbian city built by the Maya people of the Termi ...
. Rather than analyzing the site and seeing which targets appear popular, archaeoastronomers have instead examined the ethnographic records to see what features of the sky were important to the
Maya
Maya may refer to:
Civilizations
* Maya peoples, of southern Mexico and northern Central America
** Maya civilization, the historical civilization of the Maya peoples
** Maya language, the languages of the Maya peoples
* Maya (Ethiopia), a popu ...
ns and then sought archaeological correlates. One example which could have been overlooked without historical records is the Mayan interest in the planet
Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...
. This interest is attested to by the
Dresden codex
The ''Dresden Codex'' is a Maya book, which was believed to be the oldest surviving book written in the Americas, dating to the 11th or 12th century. However, in September 2018 it was proven that the Maya Codex of Mexico, previously known as t ...
which contains tables with information about Venus's appearances in the sky.
[Kelley and Milone 2005:369–70] These cycles would have been of astrological and ritual significance as Venus was associated with
Quetzalcoatl
Quetzalcoatl (, ; Spanish: ''Quetzalcóatl'' ; nci-IPA, Quetzalcōātl, ket͡saɬˈkoːaːt͡ɬ (Modern Nahuatl pronunciation), in honorific form: ''Quetzalcōātzin'') is a deity in Aztec culture and literature whose name comes from the Na ...
or
Xolotl. Associations of architectural features with settings of Venus can be found in Chichen Itza, Uxmal, and probably some other Mesoamerican sites.
The Temple of the Warriors bears iconography depicting feathered serpents associated with Quetzalcoatl or Kukulcan. This means that the building's alignment towards the place on the horizon where Venus first appears in the evening sky (when it coincides with the rainy season) may be meaningful. However, since both the date and the azimuth of this event change continuously, a solar interpretation of this orientation is much more likely.
Aveni claims that another building associated with the planet Venus in the form of Kukulcan, and the rainy season at Chichen Itza is the
Caracol. This is a building with a circular tower and doors facing the cardinal directions. The base faces the most northerly setting of Venus. Additionally the pillars of a stylobate on the building's upper platform were painted black and red. These are colours associated with Venus as an evening and morning star. However the windows in the tower seem to have been little more than slots, making them poor at letting light in, but providing a suitable place to view out. In their discussion of the credibility of archaeoastronomical sites, Cotte and Ruggles considered the interpretation that the Caracol is an observatory site was debated among specialists, meeting the second of their four levels of site credibility.
Aveni states that one of the strengths of the brown methodology is that it can explore astronomies invisible to statistical analysis and offers the astronomy of the
Incas as another example. The empire of the Incas was conceptually divided using ''ceques'', radial routes emanating from the capital at
Cusco
Cusco, often spelled Cuzco (; qu, Qusqu ()), is a city in Southeastern Peru near the Urubamba Valley of the Andes mountain range. It is the capital of the Cusco Region and of the Cusco Province. The city is the seventh most populous in Peru ...
. Thus there are alignments in all directions which would suggest there is little of astronomical significance, However, ethnohistorical records show that the various directions do have cosmological and astronomical significance with various points in the landscape being significant at different times of the year. In eastern Asia archaeoastronomy has developed from the history of astronomy and much archaeoastronomy is searching for material correlates of the historical record. This is due to the rich historical record of astronomical phenomena which, in China, stretches back into the
Han dynasty
The Han dynasty (, ; ) was an Dynasties in Chinese history, imperial dynasty of China (202 BC – 9 AD, 25–220 AD), established by Emperor Gaozu of Han, Liu Bang (Emperor Gao) and ruled by the House of Liu. The dynasty was preceded by th ...
, in the second century BC.
A criticism of this method is that it can be statistically weak. Schaefer in particular has questioned how robust the claimed alignments in the Caracol are. Because of the wide variety of evidence, which can include artefacts as well as sites, there is no one way to practice archaeoastronomy. Despite this it is accepted that archaeoastronomy is not a discipline that sits in isolation. Because archaeoastronomy is an interdisciplinary field, whatever is being investigated should make sense both archaeologically and astronomically. Studies are more likely to be considered sound if they use theoretical tools found in archaeology like
analogy and
homology and if they can demonstrate an understanding of accuracy and precision found in astronomy. Both quantitative analyses and interpretations based on ethnographic analogies and other contextual evidence have recently been applied in systematic studies of architectural orientations in the Maya area and in other parts of Mesoamerica.
Source materials
Because archaeoastronomy is about the many and various ways people interacted with the sky, there are a diverse range of sources giving information about astronomical practices.
Alignments
A common source of data for archaeoastronomy is the study of alignments. This is based on the assumption that the axis of alignment of an archaeological site is meaningfully oriented towards an astronomical target. Brown archaeoastronomers may justify this assumption through reading historical or ethnographic sources, while green archaeoastronomers tend to prove that alignments are unlikely to be selected by chance, usually by demonstrating common patterns of alignment at multiple sites.
An alignment is calculated by measuring the
azimuth
An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north.
Mathematicall ...
, the angle from north, of the structure and the altitude of the horizon it faces The azimuth is usually measured using a
theodolite
A theodolite () is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but it is also used extensively for building and ...
or a
compass
A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...
. A compass is easier to use, though the deviation of the Earth's magnetic field from true north, known as its
magnetic declination
Magnetic declination, or magnetic variation, is the angle on the horizontal plane between magnetic north (the direction the north end of a magnetized compass needle points, corresponding to the direction of the Earth's magnetic field lines) and ...
must be taken into account. Compasses are also unreliable in areas prone to magnetic interference, such as sites being supported by scaffolding. Additionally a compass can only measure the azimuth to a precision of a half a degree.
A theodolite can be considerably more accurate if used correctly, but it is also considerably more difficult to use correctly. There is no inherent way to align a theodolite with North and so the scale has to be
calibrated using astronomical observation, usually the position of the Sun. Because the position of celestial bodies changes with the time of day due to the Earth's rotation, the time of these calibration observations must be accurately known, or else there will be a systematic error in the measurements. Horizon altitudes can be measured with a theodolite or a
clinometer.
Artifacts
For artifacts such as the
Sky Disc of Nebra, alleged to be a Bronze Age artefact depicting the cosmos, the analysis would be similar to typical
post-excavation analysis
Post-excavation analysis constitutes processes that are used to study archaeological materials after an excavation is completed. Since the advent of "New Archaeology" in the 1960s, the use of scientific techniques in archaeology has grown in impor ...
as used in other sub-disciplines in archaeology. An artefact is examined and attempts are made to draw analogies with historical or ethnographical records of other peoples. The more parallels that can be found, the more likely an explanation is to be accepted by other archaeologists.
A more mundane example is the presence of
astrological symbols found on some shoes and sandals from the Roman Empire. The use of shoes and sandals is well known, but
Carol van Driel-Murray
Carol van Driel-Murray (born 20 May 1950) is a Roman archaeologist who specialises in the role of women and studying leather. After studying at the University of Liverpool, van Driel-Murray worked at the University of Amsterdam for 37 years and ...
has proposed that astrological symbols etched onto sandals gave the footwear spiritual or medicinal meanings. This is supported through citation of other known uses of astrological symbols and their connection to medical practice and with the historical records of the time.
Another well-known artefact with an astronomical use is the
Antikythera mechanism
The Antikythera mechanism ( ) is an Ancient Greek hand-powered orrery, described as the oldest example of an analogue computer used to predict astronomical positions and eclipses decades in advance. It could also be used to track the four-y ...
. In this case analysis of the artefact, and reference to the description of similar devices described by Cicero, would indicate a plausible use for the device. The argument is bolstered by the presence of symbols on the mechanism, allowing the disc to be read.
Art and inscriptions
Art and inscriptions may not be confined to artefacts, but also appear painted or inscribed on an archaeological site. Sometimes inscriptions are helpful enough to give instructions to a site's use. For example, a Greek inscription on a stele (from
Itanos) has been translated as:"Patron set this up for Zeus Epopsios. Winter solstice. Should anyone wish to know: off 'the little pig' and the stele the sun turns." From Mesoamerica come
Mayan and
Aztec codices
Aztec codices ( nah, Mēxihcatl āmoxtli , sing. ''codex'') are Mesoamerican manuscripts made by the pre-Columbian Aztec, and their Nahuatl-speaking descendants during the colonial period in Mexico.
History
Before the start of the ...
. These are folding books made from
Amatl, processed tree bark on which are
glyph
A glyph () is any kind of purposeful mark. In typography, a glyph is "the specific shape, design, or representation of a character". It is a particular graphical representation, in a particular typeface, of an element of written language. A g ...
s in
Mayan or
Aztec script
The Aztec or Nahuatl script is a pre-Columbian writing system that combines ideographic writing with Nahuatl specific phonetic logograms and syllabic signs which was used in central Mexico by the Nahua people.
Origin
The Aztec writing system d ...
. The
Dresden codex
The ''Dresden Codex'' is a Maya book, which was believed to be the oldest surviving book written in the Americas, dating to the 11th or 12th century. However, in September 2018 it was proven that the Maya Codex of Mexico, previously known as t ...
contains information regarding the Venus cycle, confirming its importance to the Mayans.
More problematic are those cases where the movement of the Sun at different times and seasons causes light and shadow interactions with
petroglyph
A petroglyph is an image created by removing part of a rock surface by incising, picking, carving, or abrading, as a form of rock art. Outside North America, scholars often use terms such as "carving", "engraving", or other descriptions ...
s. A widely known example is the Sun Dagger of
Fajada Butte
Fajada Butte is a butte in Chaco Culture National Historical Park, in northwest New Mexico.
Fajada Butte (Banded Butte) rises 135 meters above the canyon floor. Although there is no water source on the butte, there are ruins of small cliff dwell ...
at which a glint of sunlight passes over a spiral petroglyph. The location of a dagger of light on the petroglyph varies throughout the year. At the summer solstice a dagger can be seen through the heart of the spiral; at the winter solstice two daggers appear to either side of it. It is proposed that this petroglyph was created to mark these events. Recent studies have identified many similar sites in the US Southwest and Northwestern Mexico. It has been argued that the number of solstitial markers at these sites provides statistical evidence that they were intended to mark the solstices. The Sun Dagger site on Fajada Butte in Chaco Canyon, New Mexico, stands out for its explicit light markings that record all the key events of both the solar and lunar cycles: summer solstice, winter solstice, equinox, and the major and minor
lunar standstills of the moon's 18.6 year cycle.
[Cambridge U, 1982 sofaer et al.: 126] In addition at two other sites on Fajada Butte, there are five light markings on petroglyphs recording the summer and winter solstices, equinox and solar noon. Numerous buildings and interbuilding alignments of the great houses of Chaco Canyon and outlying areas are oriented to the same solar and lunar directions that are marked at the Sun Dagger site.
If no ethnographic nor historical data are found which can support this assertion then acceptance of the idea relies upon whether or not there are enough petroglyph sites in North America that such a correlation could occur by chance. It is helpful when petroglyphs are associated with existing peoples. This allows ethnoastronomers to question informants as to the meaning of such symbols.
Ethnographies
As well as the materials left by peoples themselves, there are also the reports of other who have encountered them. The historical records of the
Conquistadores are a rich source of information about the pre-Columbian Americans.
Ethnographers also provide material about many other peoples.
Aveni uses the importance of zenith passages as an example of the importance of ethnography. For peoples living between the tropics of Cancer and Capricorn there are two days of the year when the noon Sun passes directly overhead and casts no shadow. In parts of Mesoamerica this was considered a significant day as it would herald the arrival of rains, and so play a part in the cycle of agriculture. This knowledge is still considered important amongst Mayan Indians living in Central America today. The ethnographic records suggested to archaeoastronomers that this day may have been important to the ancient Mayans. There are also shafts known as 'zenith tubes' which illuminate subterranean rooms when the Sun passes overhead found at places like
Monte Albán
Monte Albán is a large pre-Columbian archaeological site in the Santa Cruz Xoxocotlán Municipality in the southern Mexican state of Oaxaca (17.043° N, 96.767°W). The site is located on a low mountainous range rising above the plain in the c ...
and
Xochicalco
Xochicalco () is a pre-Columbian archaeological site in Miacatlán Municipality in the western part of the Mexican state of Morelos. The name ''Xochicalco'' may be translated from Nahuatl as "in the house of Flowers". The site is located 38  ...
. It is only through the ethnography that we can speculate that the timing of the illumination was considered important in Mayan society. Alignments to the sunrise and sunset on the day of the zenith passage have been claimed to exist at several sites. However, it has been shown that, since there are very few orientations that can be related to these phenomena, they likely have different explanations.
Ethnographies also caution against over-interpretation of sites. At a site in
Chaco Canyon
Chaco Culture National Historical Park is a United States National Historical Park in the American Southwest hosting a concentration of pueblos. The park is located in northwestern New Mexico, between Albuquerque and Farmington, in a remote c ...
can be found a
pictograph
A pictogram, also called a pictogramme, pictograph, or simply picto, and in computer usage an icon, is a graphic symbol that conveys its meaning through its pictorial resemblance to a physical object. Pictographs are often used in writing and g ...
with a star, crescent and hand. It has been argued by some astronomers that this is a record of the
1054 Supernova. However recent reexaminations of related 'supernova petroglyphs' raises questions about such sites in general. Cotte and Ruggles used the Supernova petroglyph as an example of a completely refuted site
and anthropological evidence suggests other interpretations. The
Zuni people
The Zuni ( zun, A:shiwi; formerly spelled ''Zuñi'') are Native American Pueblo peoples native to the Zuni River valley. The Zuni are a Federally recognized tribe and most live in the Pueblo of Zuni on the Zuni River, a tributary of the Littl ...
, who claim a strong ancestral affiliation with Chaco, marked their sun-watching station with a crescent, star, hand and sundisc, similar to those found at the Chaco site.
Ethnoastronomy is also an important field outside of the Americas. For example, anthropological work with Aboriginal Australians is producing much information about their
Indigenous astronomies and about their interaction with the modern world.
Recreating the ancient sky
Once the researcher has data to test, it is often necessary to attempt to recreate ancient sky conditions to place the data in its historical environment.
Declination
To calculate what astronomical features a structure faced a coordinate system is needed. The stars provide such a system. If you were to go outside on a clear night you would observe the stars spinning around the celestial pole. This point is +90° if you are watching the North Celestial Pole or −90° if you are observing the Southern Celestial Pole.
[Ruggles 1999:18] The concentric circles the stars trace out are lines of celestial latitude, known as ''declination''. The arc connecting the points on the horizon due East and due West (if the horizon is flat) and all points midway between the Celestial Poles is the Celestial Equator which has a declination of 0°. The visible declinations vary depending where you are on the globe. Only an observer on the North Pole of Earth would be unable to see any stars from the Southern Celestial Hemisphere at night (see diagram below). Once a declination has been found for the point on the horizon that a building faces it is then possible to say whether a specific body can be seen in that direction.
Solar positioning
While the stars are fixed to their declinations the Sun is not. The rising point of the Sun varies throughout the year. It swings between two limits marked by the solstices a bit like a
pendulum
A pendulum is a weight suspended from a wikt:pivot, pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, Mechanical equilibrium, equilibrium position, it is subject to a restoring force due to gravity that ...
, slowing as it reaches the extremes, but passing rapidly through the midpoint. If an archaeoastronomer can calculate from the azimuth and horizon height that a site was built to view a declination of +23.5° then he or she need not wait until 21 June to confirm the site does indeed face the summer solstice. For more information see
History of solar observation
History (derived ) is the systematic study and the documentation of the human activity. The time period of event before the invention of writing systems is considered prehistory. "History" is an umbrella term comprising past events as well ...
.
Lunar positioning
The Moon's appearance is considerably more complex. Its motion, like the Sun, is between two limits—known as
''luni''stices rather than ''sol''stices. However, its travel between lunistices is considerably faster. It takes a
sidereal month to complete its cycle rather than the year-long trek of the Sun. This is further complicated as the lunistices marking the limits of the Moon's movement move on
an 18.6 year cycle. For slightly over nine years the extreme limits of the Moon are outside the range of sunrise. For the remaining half of the cycle the Moon never exceeds the limits of the range of sunrise. However, much lunar observation was concerned with the ''
phase'' of the Moon. The cycle from one
New Moon
In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the naked eye, except when it is silhouetted against the Sun during a solar eclip ...
to the next runs on an entirely different cycle, the
Synodic month. Thus when examining sites for lunar significance the data can appear sparse due to the extremely variable nature of the moon. See
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width ...
for more details.
Stellar positioning
Finally there is often a need to correct for the apparent movement of the stars. On the timescale of human civilisation the stars have largely maintained the same position relative to each other. Each night they appear to rotate around the celestial poles due to the Earth's rotation about its axis. However, the Earth spins rather like a
spinning top. Not only does the Earth rotate, it wobbles. The Earth's axis takes around 25,800 years to complete one full wobble. The effect to the archaeoastronomer is that stars did not rise over the horizon in the past in the same places as they do today. Nor did the stars rotate around
Polaris
Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris ( Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an apparent magnitude that ...
as they do now. In the case of the
Egyptian pyramids
The Egyptian pyramids are ancient masonry structures located in Egypt. Sources cite at least 118 identified "Egyptian" pyramids. Approximately 80 pyramids were built within the Kingdom of Kush, now located in the modern country of Sudan. ...
, it has been shown they were aligned towards
Thuban, a faint star in the constellation of
Draco. The effect can be substantial over relatively short lengths of time, historically speaking. For instance a person born on 25 December in Roman times would have been born with the Sun in the constellation
Capricorn. In the modern period a person born on the same date would have the Sun in
Sagittarius
Sagittarius ( ) may refer to:
*Sagittarius (constellation)
*Sagittarius (astrology), a sign of the Zodiac
Ships
*''SuperStar Sagittarius'', a cruise ship
* USS ''Sagittarius'' (AKN-2), a World War II US Navy cargo ship
Music
*Sagittarius (ban ...
due to the
precession of the equinoxes
In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In particu ...
.
Transient phenomena
Additionally there are often transient phenomena, events which do not happen on an annual cycle. Most predictable are events like
eclipse
An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ce ...
s. In the case of