Solstice Sun Dagger (Shallow Thoughts)

Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Sat, 20 Jun 2020

Solstice Sun Dagger

Today is the summer solstice. Happy solstice!

[Solstice sun dagger] When I was in grade school -- probably some time around 7th grade -- I happened upon an article in Scientific American about the Anasazi Sun Dagger on Fajada Butte in Chaco Canyon. On the solstices and equinoxes, a thin dagger of light is positioned just right so that it moves across a spiral that's carved into the rock.

I was captivated. What an amazing sight it must be, I thought. I wondered if ordinary people were allowed to go see it.

Well, by the time I was old enough to do my own traveling, the answer was pretty much no. Too many people were visiting Fajada Butte ... the crowds were causing erosion that actually caused the stones to move, so the alignment wasn't quite working any more. It's a good reason to disallow visitors; but still, it's sad.

Imagine my surprise when last week, a friend sent out some email: Hey want to meet on Saturday to watch the solstice petroglyph shrine?

The what? It turned out that the meeting place was less than half an hour from home. Of course I wanted in!

[Cliff that holds the solstice sun dagger] We met at 9am because no one remembered when the event happened. The petroglyph is on San Ildefonso land and not open to the public, so we were looking at it from a considerable distance, using spotting scopes and telephoto lenses. (The one pictured isn't mine, it was just conveniently framed below the cliff.)

Fortunately several people remembered roughly where to look, and we found it high on the cliff, a set of concentric circles with rays coming out of it, like a child's drawing of the sun. There was a similar companion petroglyph on a wall located at right angles to the main one.

Both features were entirely in the shade. Apparently we had a wait ahead of us.

There are worse places to wait, though, even on a warm day right beside the highway. A family of (at least four) red-tailed hawks circled in the thermals, calling to each other, occasionally being chased by smaller birds, and white-throated swifts also played in the air currents calling to each other. We chatted with each other, watched birds and admired wildflowers, keeping a safe six feet apart.

We saw the sunlit part of the cliff creep closer to the petroglyph until finally, around 11am, we saw two spires of light peek out from behind a rock. They merged as they moved toward the sun petroglyph, then gradually morphed into a shadow pointer -- or dagger -- pointing down.

We watched the shadow pointer slide gradually across the concentric circles, wondering how accurately it would hit the center. I thought it was going to miss -- but no! The shadow point hit the center of the concentric-ring sun exactly.

Way to go, ancestral puebloans!

I shot lots of images: I used my 500mm Maksutov for ingress, then, since I know focus is chancy with the Mak (its focuser is fiddly, and it's difficult to tell from the camera's viewfinder when something is in focus), I used a Canon 70-300mm zoom (with autofocus) for egress. Both sets of shots came out okay.

Afterward, I stitched the ingress photos together into a time-lapse video: Solstice Sun Dagger Time-Lapse on YouTube. It's not great cinema, but it came out a lot better than I expected.

So I may never have gotten to see the famous sun dagger on Fajada Butte. But having one just down the road is even better. This place will never stop surprising me.

(By the way, this isn't an alphabet post even though I'm due for a P and this involves a Petroglyph, because I already have two other P topics lined up that I want to talk about.)

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[ 17:35 Jun 20, 2020    More science/astro | permalink to this entry | comments ]