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Mediterranean Archaeology and Archaeometry, Vol. 14, No 3, pp. 189-196
Copyright © 2014 MAA
Printed in Greece. All rights reserved.
ON THE SOLAR CORONA PETROGLYPH
IN THE CHACO CANYON
José M. Vaquero1 & J. McKim Malville2
1Departamento de Física Aplicada, Universidad de Extremadura, Cáceres, Spain
(jvaquero@unex.es)
2Department of Astrophysical and Planetary Sciences, University of Colorado
(malville@colorado.edu)
ABSTRACT
Piedra del Sol is a free-standing rock in Chaco Canyon that marks June solstice sunrise.
The petroglyph on the south face of Piedra del Sol in Chaco Canyon may depict the solar
corona observed during the total solar eclipse of July 11, 1097 CE The southwest area of
the rock contains features consisted with a sun watching station and faces December sol-
stics sunset. During the 19th century, coronal mass ejection appears to have been ob-
served during two total solar eclipses. The petroglyph on the south face appears to show
a configuration of the solar corona that is consistent with a coronal mass ejection (CME).
The hypothesis that a CME is depicted at Piedra del Sol is testable and can be disproven
if the maximum of solar activity did not occur near 1097 CE. Recent studies indicate that
1097 CE was inded close to solar maximum. Miyahara et al. (2010) locate the maximum in
1098 CE based upon cosmogenic-isotopes. Vaquero and Trigo (2012) also found that 1098
CE was a maximum of solar cycle using a combination of documentary sources. The
eclipse of 1097 CE occurred during a period of high solar activity, consistent with the in-
terpretation of the petroglyph as a representation of solar corona during the solar eclipse
of that year.
KEYWORDS: Chaco Canyon, petroglyph, solar eclipse, coronal mass ejection
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1. INTRODUCTION
One of the more interesting petroglyphs
with possible astronomical meaning in the
southwest of USA is located in the south-
ern face of the Piedra de Sol in Chaco Can-
yon. This petroglyph can be described as
an unusual circle with curved rays, which
resemble the curved coronal structures of
the eclipsed sun during a coronal mass
ejection or, even, exaggerations of curved
polar streamers of the corona. Malville
(2008) has noted that the totality path of the
eclipse of July 11, 1097, crossed the Chaco
Canyon. In fact, it was the only visible total
eclipse during the period of maximum
great house construction (1020-1130 CE) in
Chaco Canyon. The representation of a
Coronal Mass Ejection (CME) in this petro-
glyph is a hypothesis that is impossible to
prove, but it can be tested and falsified.
2.1 Coronal Mass Ejections
During peak of solar activity, which oc-
curs approximately every 11 years, the sun
produces about three coronal mass ejec-
tions (CME) every day, while at minimum
solar activity the frequency drops to one
every five days. CMEs consist of a collec-
tion of electrons and protons entangled in a
magnetic field. Their speeds range from 20
km/sec to 3200 km/sec. Typically they
start with a slowly rising bubble near the
sun's surface, followed by rapid accelera-
tion. Most CMEs miss the earth, but when
one reaches the earth it causes a disruption
of the magnetosphere, which results in
strong auroral displays around the earth's
magnetic poles. It also may disrupt radio
transmission, endanger electrical circuits,
and damage satellites.
During the twentieth century CMEs
were reported during two total eclipses. At
the Spanish eclipse of July 18 the astrono-
mer Gugleimo Temple, stationed in Torre-
blanca, recorded in a drawing an anoma-
lous feature of the corona, which appears
to have been a CME (Figure 1). Of the 46
firsthand accounts of that eclipse that were
made across Spain, about half reported ob-
serving this feature (Eddy 1974).
Figure 1 Drawing of the eclipse of July 18, 1860 by
Tempel
The second CME was photographed in
Chile using the Schaeberle 40 foot camera
of Lick Observatory on April 16, 1893.
Schaeberle made a remarkable tracing of
prominences and structures of the corona
using eight 18x22 inch glass plates (Figure
2; Pearson 2010). Cliver (1989) has suggest-
ed the feature in the lower right that is la-
beled "comet" was another CME.
Figure 2. Drawing of coronal structures by
Schaeberle for the total eclipse 16 April 1893. A
coronal mass ejection appears in the lower right-
hand side of the figure labeled as a comet.
2.2 Piedra del Sol
In the summer of 1992, the University of
Colorado and Ft. Lewis College organized
a field school in archaeoastronomy, lead by
jointly by W. James Judge and J. McKim
Malville. During that field school, one of
the staff, Rick Watson, discovered a large
spiral petroglyph on a free standing rock
near the visitors' center in Chaco Canyon
SOLAR CORONA PETROGLYPH
191
© University of the Aegean, 2014, Mediterranean Archaeology & Archaeometry, 14, 3 (2014) 189-196
(Figures 3-6). It appeared possible that a
pyramidal rock on the northeastern hori-
zon would cast a shadow on the spiral
close to June solstice. The following sum-
mer, that possibility was confirmed by GB
Cornucopia (Watson et al. 1996). The south
face of the rock contains a number of pet-
roglyphs, including two of Kokopeli and
an unusual one that appeared to depict the
total solar eclipse of July 11, 1097 (Figures
7-10). In addition, the southwest side of the
rock contains a pecked basin and a grind-
ing area (Figures 11 & 12), which are often
found associated with astronomical observ-
ing stations in Mesa Verde (Malville and
Munson 1998). Later that year, Cornucopia
confirmed that the southwest side of the
rock faced December solstice sunset near a
prominent horizon feature. Because of the
multiplicity of solar events that appears to
be associated with the rock, we proposed
that it be named "Piedra del Sol."
Figure 3. Piedra del Sol Piedra del Sol, viewed from
the east. The side of the rock to the left,
slightly in shadow, contains the possible
coronal petroglyph.
Figure 4. Spiral petroglyph on the northeast side of
Piedra del Sol.
Figure 5. June 5 Sunrise viewed from the center
of the spiral.
Figure 6 June summer solstce viewed from the center of
the spiral.
Figure 7 Possible solar eclipse petroglyph
Figure 8 Coronal mass ejection, March 9, 2000 (SO-
HO spacecraft, NASA)
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Figure 9 South Face of Piedra del Sol showing the possible eclipse petroglyph and two Kokopeli petro-
glyphs
Figure 10 The path of the solar eclipse of 11 July
1097. Red square represents the Chaco Canyon
(eclipse predictions by Fred Espenak, NASA's
GSFC).
Figure 11 Pecked basin on west side of Piedra del Sol
Figure 12 Grinding area on west side of Piedra del Sol
2.3 Solar Activity during 1097
We use the high dependence of the ob-
served solar corona during total eclipses
upon the solar cycle to check the consisten-
cy of the hypothesis of the solar corona
represented in the petroglyph of the "Pie-
dra del Sol". If AD1097 was a year of low
solar activity, the solar corona would be
very different from the one represented in
the petroglyph in which case the hypothe-
sis of the solar corona represented in the
Chaco Canyon should be abandoned.
However, if AD1097 was a year of high so-
lar activity, the hypothesis would be
strengthened.
SOLAR CORONA PETROGLYPH
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© University of the Aegean, 2014, Mediterranean Archaeology & Archaeometry, 14, 3 (2014) 189-196
Fortunately, some recent studies can
help us to check the status of solar activity
around 1097. Therefore, the aim of this pa-
per is to show that this hypothesis is com-
patible with the state of solar activity in
this date.
We have some sources to study the past
solar activity. First, we have some docu-
mentary sources describing auroral obser-
vations (Eather 1980) or records of sun-
spots with the naked eye (Whittmann and
Xu 1987) . These records are not very ho-
mogeneous but have a high temporal reso-
lution. Moreover, we also have indirect ev-
idence of past solar activity based on cos-
mogenic radionuclides (e.g., 10Be and 14C),
which are produced by cosmic rays in the
Earth’s atmosphere. These records are
more homogeneous but have a lower tem-
poral resolution than historical documents.
Obviously, both sources have their ad-
vantages and disadvantages.
We have compiled the available infor-
mation on solar activity around AD1097 in
Figure 3. The red line represents the
smoothed sunspot number reconstructed
by Solanki et al. (2004) based on dendro-
chronologically dated radiocarbon concen-
trations. Note that the resolution of these
data is not enough to detect the 11-year so-
lar cycle. However, 1097 is located very
close to a local maximum, the first one after
the Oort Minimum (1010–1070) and the
first one belonging to a period of relatively
high solar activity called Medieval Solar
Maximum (1100–1250) (Jirikowic and Da-
mon 1994).
In Figure 13, the annual number of na-
ked-eye observations of sunspots (Vaquero
et al. 2002) is represented by the blue line
and the annual number of auroral nights
(from the catalogue compiled by Křivský
and Pejml (1998) is represented by the or-
ange line. Arrows of these colors corre-
spond to estimated maxima of solar cycle
using naked-eye observations (blue) and
auroral nights (orange) respectively
(Vaquero and Trigo 2012). Finally, green
arrows correspond to the estimated maxi-
ma of solar cycle using a high resolution
14C record from tree rings (Miyahara (2010).
Therefore, different records are available to
assess the phase of the solar cycle around
1097 using documental records and cos-
mogenic proxies. Both kinds of information
suggest that the date of maximum of the
solar cycle is close to 1098. This fact is,
therefore, a support for the hypothesis of
the solar corona represented in the petro-
glyph of the "Piedra del Sol".
Figure 13 Various solar activity proxies during the period 1055–1145. See text for details.
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© University of the Aegean, 2014, Mediterranean Archaeology & Archaeometry, 14, 3 (2014) 189-196
2.4 The Supernova of 1054CE
This is not the only petroglyph in Chaco
Canyon that has been identified with a tran-
sient astronomical event. The well-known
pictograph, containing a hand, a crescent
moon, and a 10-pointed star below the Great
House of Peñasco Blanco has been identified
(Fisher 2010) with the supernova of AD 1054.
That identification has however been ques-
tioned on several issues. The anthropologist
Florence Halley Ellis pointed out that the
rock art symbols of the pictograph are com-
mon among rock art of the Pueblos They
may have been clan symbols, and she sug-
gests the star more likely was a representa-
tion of Venus. Two other sites containing a
combination of star and crescent moon that
had been identified with the 1054 supernova
have also been recently re-evaluated and
found wanting. Their identifications with a
supernova have also been found to be un-
likely (Krupp et al. 2010)
2.4 Eclipse of 1097
In the case of the Piedra del Sol, the pu-
tative image of the corona is unique among
the rock art symbols of the American
Southwest. It certainly does not appear
elsewhere in Chaco Canyon. Furthermore,
this rock appears to have been a place for
monitoring and celebrating the cyclic be-
havior of the sun. On its east side rock the
large spiral petroglyph marks June solstice
as well as providing a 15-16 day anticipa-
tion of the event. As viewed from the cen-
ter of the spiral, the sun begins to climb the
southern edge of a pyramidal rock on the
horizon more than a month before solstice
and reaches the top of the rock on June 5.
Monitoring the movement of the sun after
solstice may well have continued past July
11, and hence people following the behav-
ior of the sun could have been in the
neighborhood of Piedra del Sol at the time
of the eclipse.
This eclipse had very good viewing con-
ditions in Chaco Canyon: it occurred in
mid-after-noon, the sun's altitude was high
(58°) and the eclipse had a long duration (4
minutes). One of the often dramatic fea-
tures of a total eclipse is the sudden ap-
pearance of Venus near the sun. At the
time of this eclipse Venus had a visual
magnitude of -4 and appeared to the east of
the sun 10o higher in the sky. The round
pecked mark above the petroglyph may
represent Venus observed during the
eclipse (Figure 9).
The petroglyph panel on the south side
of the rock contains two images of Ko-
kopeli, the flute player (Figure 8). The
presence of the flute player on a rock so
devoted to the sun raises the interesting
possiblility of a connection between flute
playing and solar ritual. We do know that
the sun plays a major role in the Blue and
Drab Flute Societies of the Hopi. Sun sym-
bols were used in the regular flute ceremo-
nies. These two societies have one day each
in winter and summer for special prayer
offerings to the sun called Tawa Baholowu
(Voth 1912). The summer ceremony of the
Drab Flute Society in June involved quartz
crystals for throwing rays of sunlight into a
medicine bowl (Voth 1903). Flutes may
have played a role in summing or bringing
up the sun.
The year 1097 lies within a transitional
period of Chacoan culture, when the Clas-
sic Bonito Phase of Great House construc-
tion was ending and a different style of so-
cial organization of the Late Bonito Period
was commencing (Van Dyke 2007). A pro-
longed drought in the Chaco Basin in the
decade of 1090 may have weakened the
credibility of ceremonies performed Chaco
Canyon to maintain sufficient agricultural
production. The drought may brought
about social tensions that caused migra-
tions out of the Canyon, such as to Salmon
Pueblo in the north. The sun must have
been an object of great importance, and its
eclipse, which would have been observed
over a large portion of the Chacoan sphere
of influence, could have further diminished
the credibility of sun rituals performed in
canyon. The eclipse may thus have been
more significant than a puzzling event in
the sky. Because the eclipse was concomi-
tant with environmental and social changes
in the canyon, it may warranted a record-
ing on the rock of Piedra del Sol.
SOLAR CORONA PETROGLYPH
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ACKNOWLEDEMENTS
The authors are grateful to I.G. Usoskin and H. Miyahara for their comments and data.
Support from the Junta de Extremadura (Research Group Grant No. GR10131) and Span-
ish Government (AYA 2011-25945) is gratefully acknowledged.
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