The Sun’s corona is bright, but far dimmer than the surface of the star, meaning it's usually invisible to the naked eye. However, there is one time when the corona becomes starkly visible. When the Sun's light is blocked by the Moon moving in front it during a solar eclipse, it becomes possible to see the corona is brightly snaking out from the edges of the shadow where the Sun once shone. During a solar eclipse, it is also be possible to see the tendrils of a coronal mass ejection, silhouetted against the sky.
To Malville, the petroglyph etched into the side of Piedra del Sol was almost certainly a depiction of such a striking celestial event by a Pueblo artist. "This pictrograph is unique," Malville says. "There's no other kind of rock art object that I know of that has this shape to it."
In a study published in 2014 in the journal Mediterranean Archaeology and Archaeometry, he set out to prove a connection between what he saw in the rock carving and what the heavens were doing at the time. If the petroglyph did indeed depict an eclipse, he thought, it could shed light on the special relationship that existed between the Pueblo people and the Sun.
Based on calculations of the orbits of the Moon and Earth, Malville notes that a total solar eclipse was visible in the Chaco Canyon area on July 11, 1097, around the height of the area's development. However, this alone didn't prove that the drawing on the petroglyph actually showed a coronal mass ejection. That’s because the chance of both a solar eclipse and a coronal ejection occurring in tandem are slight.
"We can list on one hand the number of times a coronal mass ejection has been observed during an eclipse," Malville says, noting that the most recent occurrence happened in 2012.
One of the few previous observed occurrences was in 1860, when a Spanish astronomer managed to sketch out a coronal mass ejection during a solar eclipse. That drawing that strongly resembles the Piedra del Sol petroglyph.
