Rock Art in Chaco Canyon May Depict Ancient Solar Eclipse, Experts Say

On the eve of North America’s first solar eclipse in the 21st century, a pair of astronomers say that an obscure piece of rock art in New Mexico’s Chaco Canyon may depict a similar celestial event that took place 920 years ago.

The glyph, made on a sandstone boulder known as Piedra del Sol, portrays a circle bursting with curved tendrils and curlicues, which the researchers say resemble the filamentous fringe of an especially active sun when it disappears behind the moon.

“It looks like a circular feature with curved tangles and structures,” said J. McKim Malville, an astrophysicist at the University of Colorado, in a recent press statement.

“If one looks at a drawing by a German astronomer of the 1860 total solar eclipse during high solar activity, rays and loops similar to those depicted in the Chaco petroglyph are visible.”

During an eclipse, curls and whorls can sometimes be seen, formed by giant jets of plasma — known as coronal mass ejections, or CMEs — that the sun releases when it’s at or near the peak of its 11-year cycle.

And the astronomers report that on July 11, 1097, an eclipse passed directly over the Chaco Canyon area when the Ancestral Puebloan culture in the canyon was burgeoning — and when the sun was, indeed, near its peak.

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A drawing of the 1860 eclipse, made by German astronomer Wilhelm Tempel, is said by some experts to resemble the Chaco Canyon petroglyph.

(Discover new insights into Chaco’s leadership: “Elite ‘Dynasty’ at Chaco Canyon Got Its Power From One Woman, DNA Shows“)

“This was a testable hypothesis,” Malville said.

“It turns out the sun was in a period of very high solar activity at that time, consistent with an active corona and CMEs.”

Malville and his colleague, José Vaquero of Spain’s University of Extremadura, drew on a number of diverse sources to determine whether the eclipse of 1097 occurred during a time of intense solar activity.

First, they checked the chemical record that’s enshrined in tree rings.

The ongoing bombardment of Earth by cosmic radiation — from sources other than the sun — results in the production of the isotope carbon-14. But periods of intense solar activity interferes with this process. So, higher solar activity shows up in the rings of trees as lower amounts of carbon-14.

The duo also reviewed historical records from around northern Europe in the 11th century, to assess the number of nights that the region experienced auroras, the Northern lights caused by solar emissions.

They even consulted the reports of ancient Chinese astronomers, who used naked-eye observations to record the sun’s annual patterns of sun spots — cool spots that indicate less solar activity.

In their report of their findings, Malville and Vaquero say that chemical evidence and human documents alike support the theory that a solar maximum occurred near the 1097 eclipse.

“Both kinds of information suggest that the date of maximum of the solar cycle is close to 1098,” they write.

“This fact is, therefore, a support for the hypothesis of the solar corona represented in the petroglyph of the Piedra del Sol.”

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The Piedra del Sol petroglyph.

The findings fit within the well-known astronomical uses of Chaco Canyon’s rock art, the researchers add.

(See a major rock-art find in Arizona: “Thousands of Ancient Petroglyphs, ‘Dramatic’ Solar Calendar Reported in N. Arizona‘)

Among the most famous pictographs in the canyon is the likely representation of the supernova of 1054, for example.

And on the east face of Piedra del Sol there’s a spiral-shaped petroglyph that’s bisected by a triangular shadow for about two weeks before the summer solstice.

(See a recent rock-art find in Arizona mark the solstice: “Photos: Watch the ‘Shadow Dagger’ Solar Calendar Mark the Equinox“)

Whether created by Ancestral Puebloan artisans of records of celestial events, or as ways to mark them, such glyphs demonstrate that rock art often served as astronomical purpose.

“This possible eclipse petroglyph on Piedra del Sol is the only one we know of in Chaco Canyon,” Malville said in the statement.

“I think it is quite possible that the Chacoan people may have congregated around Piedra del Sol at certain times of the year and were watching the sun move away from the summer solstice when the eclipse occurred.”

Malville and Vaquero initially reported their research in 2014, in the Journal of Mediterranean Archaeology and Archaeometry.

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  1. Vanessa L L CHRISMAN

    What is the current thought of the relationship between Chaco Canyon and Mesa Verde. Considering that both had outlayers and roads. Each their own distinct way of building and pottery.

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