With any luck I’ll finally post about last week’s trip to Las Vegas soon, but meanwhile, here’s something interesting that we spotted a couple of times on the drive back: The shadow of a contrail against the sky.

Here’s what it looked like, as the camera saw it. Actually, it was much more visible at the start. It faded considerably in the time it took to get the camera out and snap the photo.

And here it is with the contrast enhanced. You can see a dark line extending across the sky from the end of the trail down to the lower left. The sun was at the upper right, almost but not quite in line with the trail at that point.

Atmospheric Optics has a huge collection of cloud shadows, rays, rainbows, ice halos, and more, including a diagram of how contrail shadows work.