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Archaeoastronomy

2007 Schools Wikipedia Selection. Related subjects: Space (Astronomy)

   The sun rising over Stonehenge at the 2005 Summer Solstice.
   Enlarge
   The sun rising over Stonehenge at the 2005 Summer Solstice.

   Archaeoastronomy (also spelled Archeoastronomy) is the study of ancient
   or traditional astronomies in their cultural context, utilising
   archaeological and anthropological evidence. The anthropological study
   of astronomical practices in contemporary societies is often called
   ethnoastronomy, although there is no consensus as to whether
   ethnoastronomy is a separate discipline or is a part of
   archaeoastronomy. Archaeoastronomy is also closely associated with
   historical astronomy, the use of historical records of heavenly events
   to answer astronomical problems and the history of astronomy, which
   uses written records to evaluate past astronomical traditions.

   It is most frequently mentioned with astronomical claims regarding
   Stonehenge or the pyramids of Egypt.

History of archaeoastronomy

   Archaeoastronomy is almost as old as archaeology itself. Heinrich
   Nissen was arguably the first archaeoastronomer, publishing Das
   Templum: Antiquarische Untersuchungen in 1869. Other researchers
   followed. The astronomer Norman Lockyer was active at the end of the
   nineteenth century and the start of the twentieth. His studies included
   an examinations of Egyptian temples in The Dawn of Astronomy in 1894
   and of Stonehenge published as Stonehenge and Other British Stone
   Monuments Astronomically Considered in 1906. The archaeologist Francis
   Penrose published extensively in the Philosophical Transactions of the
   Royal Society on the astronomical alignment of Greek temples in the
   Mediterranean in the same period. Archaeoastronomy was, for a while, a
   respectable subject. The first issue of the archaeological journal
   Antiquity includes an article on archaeoastronomical research.
   Early archaeoastronomy began by surveying alignments of Megalithic
   stones in the British Isles and sites like Auglish in Co.Derry in an
   attempt to find statistical patterns
   Enlarge
   Early archaeoastronomy began by surveying alignments of Megalithic
   stones in the British Isles and sites like Auglish in Co. Derry in an
   attempt to find statistical patterns

   In the British Isles interest in archaeoastronomy waned until the 1960s
   when the astronomer Gerald Hawkins proposed that Stonehenge was a
   Neolithic computer. Around the same time the engineer Alexander Thom
   published his survey results of megalithic sites also proposed
   widespread practice of accurate astronomy in the British Isles. The
   claims of Hawkins were largely dismissed. However, Thom's analysis
   continued to pose a problem. A re-evaluation of Thom's fieldwork by
   Clive Ruggles attempted to show that his claims of high accuracy
   astronomy were not fully supported by the evidence. Nevertheless there
   was evidence of widespread interest in astronomy associated with
   megalithic sites. The response from most archaeologists was tepid. Only
   one, Euan MacKie, recognised that Thom's theories needed to be tested
   and he excavated at the Kintraw 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 site) led him to check Thom's geometrical
   theories at the Cultoon stone circle in Islay, also with a positive
   result. MacKie therefore broadly accepted Thom’s conclusions and
   published new prehistories of Britain.. Until the early 1980s – with
   the exception just mentioned – most archaeoastronomical research in the
   United Kingdom was concerned with establishing the existence of
   astronomical alignments in prehistoric sites by statistical means
   rather than the social practice of astronomy in ancient times.
   It has been proposed that Maya sites such as Uxmal were built in
   accordance with astronomical alignments
   Enlarge
   It has been proposed that Maya sites such as Uxmal were built in
   accordance with astronomical alignments

   In the New World, anthropologists began to more fully consider the role
   of astronomy in Amerindian societies. This approach had access to
   sources that the prehistory of Europe lacks such as ethnographies and
   the historical records of the early colonisers. 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 comparatively weak when compared to
   the statistically led investigations in Europe.

   This came to a head at a meeting sponsored by the IAU in Oxford 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.

Methodology

   Because of the wide variety of evidence, which can include artefacts as
   well as sites there is no one way practise 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.

Artefactual analysis

   The Antikythera mechanism (main fragment)
   Enlarge
   The Antikythera mechanism (main fragment)

   In the case of artefacts 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 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.

   Another well-known artefact with an astronomical use is the Antikythera
   mechanism. 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.

Symbolic analysis

   Diagram showing the location of the sun daggers on the petroglyph on
   various days
   Enlarge
   Diagram showing the location of the sun daggers on the petroglyph on
   various days

   In some cases the use of an artefact may be known, but its meaning may
   not be fully understood. In such cases an examination of the symbolism
   on the artefact may be necessary.

   A 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 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.

   More problematic are some petroglyphs. Symbols on rock are one such
   class of symbol which are occasionally argued to posses astronomical
   meanings. An example is the Sun Dagger of Fajada Butte which is a glint
   of sunlight passing over a spiral petroglyph. The location of the
   dagger on the petroglyph varies throughout the year. At the solstices a
   dagger can be seen either through the heart of the spiral or to either
   side of it. It is proposed that this petroglyph was created to mark
   these events. If no ethnographic nor historical data are found which
   can support this assertion then acceptance of the idea relies upon the
   reader's own belief as to 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.

Alignment analysis

   The Sun rising behind the Heel Stone at Stonehenge
   Enlarge
   The Sun rising behind the Heel Stone at Stonehenge

   The most public image of archaeoastronomy is the practice of alignment
   analysis. This is the study of the orientation of structures and
   calculating the direction in which they face. In the case of Stonehenge
   it is well known to face the rising midsummer sun. In the case of the
   pyramids of Egypt they face north, probably to face the circumpolar
   stars.

   The use of alignment analysis may vary depending upon the researcher.
   As a coarse stereotype archaeoastronomers from an historical background
   tend to have an idea which is then tested by examining structures for
   alignments. Astronomically-minded archaeoastronomers may analyze large
   numbers of sites and attempt to find statistical patterns. This
   approach was particularly employed in early papers by pioneers in the
   field such as Alexander Thom who conducted extensive fieldwork at
   megalithic sites and concluded many sites were situated to observe the
   moon. In this instance the aim was to prove that there is an
   astronomical problem which requires an historical explanation. This
   latter approach continues to an extent in some modern research but it
   has comparatively little direct impact on mainstream archaeology.

   One reason the statistically-led approach has proven unpopular with
   archaeologists and anthropologists was stated by the anthropologist
   Keith Kintigh:


   Archaeoastronomy

   In light of the fact that archaeoastronomers bring considerable energy
      and expertise to their efforts, what accounts for archaeologists'
                                indifference?

           I think the principal reason is that archaeologists see
        archaeoastronomers as answering questions that, from a social
     scientific standpoint, no one is asking. To put it bluntly, in many
   cases it doesn't matter much to the progress of anthropology whether a
     particular archaeoastronomical claim is right or wrong because the
       information doesn't inform the current interpretive questions."


   Archaeoastronomy

   Recent statistically led research has tended to be more discriminating,
   choosing archaeologically associated sites and where possible referring
   back to historical or ethnographic records to place the findings in a
   social context.

   An alignment calculated by measuring the azimuth, the angle from north,
   of the structure and the altitude of the horizon it faces. The azimuth
   is usually measured using a theodolite or a compass. A compass is
   easier to use, though the deviation of the Earth's magnetic field from
   true north, known as its magnetic declination 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 thedolite 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, else there will be a systematic
   error in the measurements. If one is measuring buildings which were
   unlikely to be orientated by their builders to within fractions of a
   degree then a thedolite can be more trouble than it is worth. Horizon
   altitudes can be measured with a theodolite or a clinometer.

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

   A time lapse photo showing the stars rotating around the celestial
   pole.
   Enlarge
   A time lapse photo showing the stars rotating around the celestial
   pole.

   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 +90º if you are watching the North
   Celestial Pole or -90º if you are observing the Southern Celestial
   Pole. The concentric circles the stars trace out are lines of celestial
   latitude, known as declination. The point on the horizon due East, if
   the horizon is flat is the celestial equation which has a declination
   of 0º. 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 if a specific
   body can be seen in that direction.
   Diagram of the visible portions of sky at varying latitudes.
   Enlarge
   Diagram of the visible portions of sky at varying latitudes.

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, slowing as it
   reaches the extremes, but passing rapidly through the mid-point. If an
   archaeoastronomer can calculate from the azimuth and horizon height
   that a site was built to view a declination of +23.5º then he need not
   wait until June 21 to confirm the site does indeed face the summer
   solstice. For more information see History of solar observation.

Lunar positioning

   The Moon's appearance is considerably more complex. Its motion, like
   the Sun, is between two limits - known as lunastices rather than
   solstices. However its travel between lunastices 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
   lunastices 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 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 the extremely variable
   nature of the moon. See Moon for more details.

Stellar positioning

   Precessional movement.
   Enlarge
   Precessional movement.

   Finally there is often a need to correct for the apparent movement of
   the stars. On the timescale of human civilisation the stars have
   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
   25700 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 as they do now. In the case of the Egyptian pyramids, it
   has been shown they were aligned towards Thuban, a faint star in the
   constellation of Draco. The effect can be substanstial over relatively
   short lengths of time, historically speaking. For instance a person
   born on December 25 in Roman times would have been born under the
   astrological sign of Capricorn. In the modern period a person born on
   the same date is now a Sagittarian due to the precession of the
   equinoxes.

Transient phenomena

   Halley's Comet depicted on the Bayeux tapestry
   Enlarge
   Halley's Comet depicted on the Bayeux tapestry

   Additionally there are often transient phenomena, events which do not
   happen on an annual cycle. Most predictable are events like eclipses.
   In the case of solar eclipses these can be used to date events in the
   past. A solar eclipse mentioned by Herodotus enables us to date a
   battle between the Medes and the Lydians, which following the eclipse
   failed to happen, to May 28, 585 BC. Other easily calculated events are
   supernovae whose remains are visible to astronomers and therefore their
   positions and magnitude can be accurately calculated.

   Some comets are predictable, most famously Halley's Comet. Yet as a
   class of object they remain unpredictable and can appear at any time.
   Some have extremely lengthy orbital periods which means their past
   appearances and returns cannot be predicted. Others may have only ever
   passed through the solar system once and so are inherently
   unpredictable.

   Meteor showers should be predictable, but the meteors are cometary
   debris and so require calculations of orbits which are currently
   impossible to complete. Other events noted by ancients include aurorae,
   sun dogs and rainbows all of which are as impossible to predict as the
   ancient weather, but nevertheless may have been considered important
   phenomena.

Major topics of archaeoastronomical research

The use of calendars

   Aztec Stone of the Sun replica in El Paso, Texas, cast from the
   original to be found in the National Museum of Anthropology and
   History. A religious artefact showing how the Mexica people thought
   about time.
   Enlarge
   Aztec Stone of the Sun replica in El Paso, Texas, cast from the
   original to be found in the National Museum of Anthropology and
   History. A religious artefact showing how the Mexica people thought
   about time.

   A common justification for the need for astronomy is the need to
   develop an accurate calendar for agricultural reasons. Ancient texts
   like Hesiod’s Works and Days, an ancient farming manual, would appear
   to contradict this. Instead astronomical observations are used in
   combination with ecological signs, such as bird migrations to determine
   the seasons. Ethnoastronomical work with the Mursi of Ethiopia shows
   that haphazard astronomy continued until recent times in some parts of
   the world. All the same, calendars appear to be an almost universal
   phenomenon in societies as they provide tools for the regulation of
   communal activities.

   An example of a non-agricultural calendar is the Mayan Tzolkin which is
   a cycle of 260 days. This count is based on an earlier calendar and is
   found throughout Mesoamerica. This formed part of a more comprehensive
   Maya Calendar which combined a series of astronomical observations and
   ritual cycles.

   Other peculiar calendars include ancient Greek calendars. These were
   nominally lunar, starting with the New Moon. In reality the calendar
   could paused or days skipped with confused citizens inscribing dates by
   both the civic calendar and ton theoi, by the moon. The lack of any
   universal calendar for ancient Greece suggests that coordination of
   panhellenic events such as games or rituals could be difficult and that
   astronomical symbolism may have been used as a politically neutral form
   of timekeeping.

Myth and cosmology

   The constellation Argo Navis drawn by Johannes Hevelius in 1690.
   Enlarge
   The constellation Argo Navis drawn by Johannes Hevelius in 1690.

   Another motive for studying the sky is to understand and explain the
   universe. In pre-scientific times myth was a tool for achieving this
   and the explanations, while not scientific, are cosmologies.

   The Incas arranged their empire to demonstrate their cosmology. The
   capital, Cusco, was at the centre of the empire and connected to it by
   means of ceques, conceptually straight lines radiating out from the
   centre. These ceques connected the centre of the empire to the four
   suyus, which were regions defined by their direction from Cusco. The
   notion of a quartered cosmos is common across the Andes. Gary Urton,
   who has conducted fieldwork in the Andean villagers of Misminay, has
   connected this quartering with the appearance of the Milky Way in the
   night sky. In one season it will bisect the sky and in another bisect
   it in a perpendicular fashion.

   The importance of observing cosmological factors is also seen on the
   other side of the world. The Forbidden City in Beijing is laid out to
   follow cosmic order though rather than observing four directions the
   Chinese saw five, North, South, East, West and Centre. The Forbidden
   City occupied the centre of ancient Beijing. One approaches the Emperor
   from the south, thus placing him in front of the circumpolar stars.
   This creates the situation of the heavens revolving around the person
   of the Emperor. The Chinese cosmology is now better known through its
   export as Feng Shui.

   There is also much information about how the universe was thought to
   work stored in the mythology of the constellations. The Barasana of the
   Amazon plan part of their annual cycle based on observation of the
   stars. When their constellation of the Caterpillar-Jaguar falls they
   prepare to catch the pupating caterpillars of the forest as they fall
   from the trees. This provides planning for food procurement at a time
   when hunger could otherwise be a problem.

   A more well-known source of constellation myth are the texts of the
   Greeks and Romans. The origin of their constellations remains a matter
   of continuing and occasionally fractious debate.

Displays of power

   The Intihuatana ("tie the sun") at Machu Picchu is believed to have
   been designed as an astronomic clock by the Incas, while some have
   speculated about the site's possible astrological role
   Enlarge
   The Intihuatana ("tie the sun") at Machu Picchu is believed to have
   been designed as an astronomic clock by the Incas, while some have
   speculated about the site's possible astrological role

   The most common popular image of archaeoastronomy is the expression of
   hidden knowledge and power. By using stellar symbolism one can make
   claims of heavenly power.

   By including celestial motifs in clothing it becomes possible for the
   wearer to make claims the power on Earth is drawn from above. It has
   been said that the Shield of Achilles described by Homer is also a
   catalogue of constellations. In North America shields depicted in
   Comanche petroglyphs appear to include Venus symbolism.

   Solsticial alignments also can be seen as displays of power. In Egypt
   the temple of Amun-Re at Karnak has been the subject of much study.
   Evaluation of the site, taking into account the change over time of the
   obliquity of the ecliptic show that the Great Temple was aligned on the
   rising of the midwinter sun. The length of the corridor down which
   sunlight would travel would have limited illumination at other times of
   the year.

   In a later period the Serapeum in Alexandria was also said to have
   contained a solar alignment so that, on a specific sunrise, a shaft of
   light would pass across the lips of the statue of Serapis thus
   symbolising the Sun saluting the god.

   The use of astronomy at Stonehenge continues to be a matter of vigorous
   discussion.

Archaeoastronomical organisations and publications

   There are currently two academic organisations for scholars of
   archaeoastronomy. ISAAC—the International Society for Archaeoastronomy
   and Astronomy in Culture—was founded in 1995 and now sponsors the
   Oxford conferences and Archaeoastronomy – the Journal of Astronomy in
   Culture. SEAC—the Société Européenne pour l’Astronomie dans la
   Culture—is slightly older; it was created in 1992. SEAC holds annual
   conferences in Europe and publishes refereed conference proceedings on
   an annual basis.

   Additionally the Journal for the History of Astronomy publishes many
   archaeoastronomical papers. For twenty-seven volumes it also published
   an annual supplement Archaeoastronomy.

Placemarks

     * Ancient Monuments Placemarks, site coordinate spreadsheets, and
       calculators.

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