Pilot’s glory is an optical illusion that makes it appear like a plane’s shadow is being lit up by a rainbow-colored halo. It might look like an eerie sign of supernatural intervention, but there is some science behind it.
Take a look at this footage (below) shared by Southwest Airlines last month. Filmed by a passenger on a commercial airplane, it shows the shadow of the aircraft on the clouds below surrounded by a bright circular rainbow. As the shadow moves, the glory appears to move with it.
Also known as a glory or pilot’s bow, pilot’s glory is produced by similar processes that create a rainbow, but with a twist.
The phenomenon actually has very little to do with the shadow. It simply occurs in the same location as the shadow because this is the antisolar point, the point directly opposite the Sun from an observer's perspective. In other words, the Sun is directly behind the shadow and the glory from the viewer.
The rainbow color is produced by water droplets above the cloud that scatter the sunlight back towards a source of light.
Truth be told, scientists still aren’t totally decided on how glories are formed and the theories are pretty complex.
We do know, however, that they appear in a number of other circumstances. Before aviation, glories were sometimes seen by climbers when they looked down a mountain at their own shadow with the sun directly behind them.
One of the earliest descriptions of the phenomenon comes from 1735 by a group of French explorers climbing the Peruvian Andes. They describe it as: “a phenomenon which must be as old as the world, but which no one seems to have observed so far… What seemed most remarkable to us was the appearance of a halo or glory around the head, consisting of three or four small concentric circles, very brightly colored, each of them with the same colors as the primary rainbow, with red outermost.”
Interestingly, they also point out another peculiar feature of glories: “The most surprising thing was that, of the six or seven people that were present, each one saw the phenomenon only around the shadow of his own head, and saw nothing around other people’s heads.”