A cloud shadow

On September 26, 2023, I saw something in the sky I did not understand. But in time, I figured it out.

In a yellow-blue hazy sky near sunset, there's a darker arc visible in the sky that has a somewhat similar shape to a cloud above and to the left if it.

This is essentially the same photo, but with a lot of extra annotations on it. The sky in the distance is yellower but the sky overhead is bluer, creating an illusion that the haze isn't really present where the viewer is. The image's annotations illustrate how the wildfire haze creates a layer that a shadow can be 'projected' onto, despite being largely invisible where the shadow's formed more overhead.

Correction to annotations on this second image: in the image, I claim it's rare for a cloud shadow like this to form. It is not. Seeing a cloud shadow against a sky this color, though, is at least uncommon where I live on the east coast of the US. I also claim the clouds forming the shadow are high-altitude clouds. I've gotten more cautious with my claims since writing these annotations, and I'm not yet good at cloud identification, so I now hesitate to say they're alto- (mid-level) vs strato- (high-level) clouds, or that one of the clouds truly is at the level of the airplane contrail visible at the top of the image. It would be better to describe these clouds as "clouds higher in the sky than their shadow seems to be."

To do: write the actual story