Archeoastronomy in Stone: How Ancestral Pueblo People Marked the Sky

The Ancestral Pueblo people carved petroglyphs and painted pictographs to follow the cycles of the sun, moon and stars, the equinoxes and solstices, and to record extraordinary events in the sky. They tied these cycles to cultural events and ceremonies of the seasons, such as planting, and even oriented settlements, buildings and architectural features to mark astronomical time. Examples include Sun Temple at Mesa Verde National Park, the Aztec West great house and Great Kiva at Aztec Ruins National Monument, and the building complexes of Chaco Culture National Historical Park.

Archeoastronomy (or archaeoastronomy) is the study of how people in the past understood what they saw in the sky, how they used it, and its place in their cultures.

Equinoxes and solstices

The sky turns like clockwork, and by watching it people could predict and prepare for the seasons.

• An equinox comes twice a year, in March and September, when the sun crosses Earth's equator and day and night are equal. Marking them helped people prepare for the coming spring and fall.
• The winter solstice, in late December, marks the start of winter and the return of light as days lengthen. The summer solstice, in June, is the longest day of the year.

Solar markers

Holly House, Hovenweep National Monument. A spiral and a set of concentric circles near Holly House mark the summer solstice: that day, a beam of sunlight enters a narrow opening across from the panel and cuts across the petroglyphs.

Two spiral petroglyphs near Holly House. NPS photo.

Puerco Pueblo, Petrified Forest National Park. The Puerco Pueblo Trail leads to a boulder with a small spiral petroglyph. On the morning of the summer solstice, a shaft of light falls on the boulder and moves down its side to touch the center of the spiral.

The Puerco Pueblo solar marker. NPS photo.

The solar marker at Puerco Pueblo. NPS photo.

Fajada Butte, Chaco Culture National Historical Park. The Sun Dagger is believed to have marked the summer and winter solstices and the equinoxes. Depending on the season, a spot of sunlight appeared at the spirals, stretched into a dagger shape, crossed them and disappeared. Erosion from foot traffic has since shifted the slabs, so the dagger no longer crosses the spiral's center as it once did, and the site is closed to the public.

Events in the sky

Rock art also marked rare celestial events, some recorded by cultures around the world.

A supernova, 1054. A pictograph on the Peñasco Blanco trail at Chaco Canyon may show the star that exploded on July 5, 1054. The supernova appeared in Taurus beside a waning crescent moon and was visible in daylight for more than three weeks. The pictograph shows the waning moon and the exploding star; a hand may point to the horizon where the supernova rose an hour and forty-five minutes before sunrise, and concentric circles may represent the not-yet-risen sun, or possibly a comet.

A pictograph that may depict the exploding star. NPS photo.

A solar eclipse, 1097. A total solar eclipse crossed the Southwest on July 11, 1097. A Chaco petroglyph may record it: a filled circle with squiggly lines around its edge and a small filled circle to the upper left, perhaps the eclipsed sun and the planet Venus.

The "squiggly sun" petroglyph at Chaco. NPS photo.

Protecting rock art

People marked rock to track time and seasons, knowing when to plant, celebrate, rest and remember. Today tribal descendants and visitors alike find personal and cultural meaning in these images. They are fragile and irreplaceable: take photographs, but do not touch or disturb them or the rock around them.

Sources

• National Park Service, "Archeoastronomy in Stone": https://www.nps.gov/articles/000/archeoastronomy-in-stone.htm
• Aztec Ruins National Monument, "Archaeoastronomy": https://www.nps.gov/azru/learn/nature/archeoastronomy.htm
• The NPS article spells the trail "Penasco Blano"; this page uses "Peñasco Blanco," as in the park's own trail page.