Pilots and frequent fliers are no doubt familiar with the phenomena, but for infrequent fliers like myself (I will qualify for a free flight sometime in the middle or late Anthropocene epoch), this was new. We were headed east in the late afternoon approaching Las Vegas when I saw a strange optical effect in the clouds directly opposite from the sun. I could see a spectrum of colors, but it was most certainly not a rainbow, although some of the same optical physics principles turn out to be involved.
I zoomed on the colorful arc for a better look. I vaguely remembered hearing about the phenomenon but for the life of me I couldn't remember the name. It's called a "glory", or in more modern times, the "glory of the pilot". It happens when the observer has the sun behind, and clouds in front. Light is backscattered in the water droplets of the cloud and diffracted, and as such is similar to the formation of a rainbow, but is different in size and pattern. According to (the always dependable) sources on the Internet, the dynamics of the light pathways are not fully understood. It was first noted by mountain climbers, where it was associated with an apparently magnified shadow of the observer called a Brocken spectre. The climber will see the colorful arc surrounding their head like a halo.
Luckily, we were descending for our landing at Vegas, and we passed right through the clouds, so I was able to catch a few shots of the airplane version of a Brocken spectre: the glory around the shadow of the plane we were in. It was small at first, but then we passed right next to a tall cumulus cloud, and the image was much larger (below). The placement of the glory actually reveals what part of the plane I was sitting in!
The Airliner Chronicles is one of my on-again/off-again serial features, which is usually updated whenever I fly somewhere.