SOLSTICE — The Sky Over Chaco Canyon

Summer solstice sunrise over Chaco Canyon: Fajada Butte, down the canyon past Una Vida, Hungo Pavi, Chetro Ketl, Pueblo Bonito and Kin Kletso, with Pueblo Alto on the mesa above, and west to Peñasco Blanco. USGS lidar, NAIP aerial photography, the Sun where it really is, rendered with forge3d.

Right now

The sky over the canyon

Chaco's builders watched this sky. The canyon walls decide when the Sun actually reaches each great house, so everything here is measured against the skyline each site really sees, not a flat horizon.

Sun

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Moon

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Sunrise at Pueblo Bonito

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Next turning point

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The horizon calendar

Where the Sun comes up

Through the year the sunrise walks along the horizon: north to the summer solstice, where it seems to stand still for a few days, then south to the winter solstice and back. In historic times Pueblo sun watchers tracked those positions against notches and peaks on the skyline to set the ceremonial calendar. Here is the actual skyline from each site, from USGS elevation data, with every sunrise of the year on it.

sunrise, every third day today moonrise limits, major standstill minor standstill skyline heights exaggerated so they show

Summer solstice

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Winter solstice

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Today

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Rendered with forge3d

Two dawns, one camera

The same view up the canyon past Fajada Butte, a few minutes after sunrise on the two solstices. In June the Sun comes up at about 63°, north of east, and throws Fajada's shadow west-southwest; in December it rises at about 123°, far to the south, and the shadow swings round to the west-northwest.

Chaco Canyon from above Chacra Mesa at summer solstice sunrise, Fajada Butte casting a long shadow — Summer solstice

The same view at winter solstice sunrise, shadows pointing the other way — Winter solstice

Looking south from the north rim over Pueblo Bonito and Chetro Ketl to Casa Rinconada at summer solstice sunrise — From the north rim near Pueblo Alto, over Pueblo Bonito and Chetro Ketl to Casa Rinconada.

Pueblo Bonito from the air an hour after the June sunrise: the D-shaped great house with its room blocks and round kivas, the north canyon wall behind it and the boulders of Threatening Rock, which fell in 1941 — Pueblo Bonito from above the canyon floor on the June solstice, about an hour after the Sun first touches the open horizon: the D-shaped great house, its rooms and kivas, and the boulders of Threatening Rock, which fell in 1941.

Terrain: USGS 3DEP lidar, drawn in nested layers so the ground near the camera is as sharp as the data allows: 0.5 m around the great houses, from the point clouds of the newer CO_CONMGaps_D24 survey, and 1 m elsewhere. Colour: USDA NAIP aerial photography, 2022, at its native 0.6 m close up. The Sun is placed for the date and time shown with forge3d's solar calculator.

Fajada Butte

The Sun Dagger

Near the top of Fajada Butte three sandstone slabs lean against the cliff. Behind them, two spirals are pecked into the rock. Around midday the gaps between the slabs let through narrow blades of light: at the summer solstice one passes through the center of the large spiral, at the winter solstice two frame it on either side, and at the equinoxes a smaller one crosses the small spiral.

The artist Anna Sofaer found it in 1977 while recording rock art. One of the slabs shifted in 1989, probably from erosion made worse by visitors, so the markings are no longer exact, and the butte is closed to protect what's left.

Next dagger day

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The 18.6-year cycle

The Moon's long swing

The Sun's rising point swings between the two solstices every year. The Moon's swings between its own limits every month, and those limits widen and narrow over 18.6 years. At a major standstill the Moon rises far north and far south of anywhere the Sun ever reaches; at a minor standstill, nine years later, it stays well inside them.

The same Fajada spiral is thought to mark this too, with shadows from the rising Moon reaching its edge at the major standstill and its center at the minor one. At Chimney Rock, a Chacoan great house 150 km to the northeast, the Moon rises between two stone pillars only around a major standstill.

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Lines on the land

Sight lines from Pueblo Bonito

From the selected site: where the Sun rises today, where it rises at each solstice, and the farthest the Moon reaches at a major standstill, all over that site's real skyline. Click any site to move the lines.

sunrise today summer solstice sunrise winter solstice sunrise moonrise, major standstill

The places

Great houses, a great kiva and a butte

A few of Chaco's sky stories are better known than they are proven. The solstice light in Casa Rinconada falls through a window that was rebuilt in the 1930s, and the 1054 supernova reading of the Peñasco Blanco pictograph is a strong case, not a certainty. They're marked as such here.