How does the bright ‘rainbow appearing’ ring that appears with of a shadow of a large jet form on the clouds below?
That colored ring is called a glory. Glories are commonly seen while you’re traveling by airplane near the level of the clouds. To see one, you need to be sitting so that the sun is directly behind your head. As you look toward a cloud, also look for the shadow of the airplane. The plane’s shadow might be surrounded by a muti-colored ring of light –and that’s the glory.
The plane’s shadow doesn’t have anything to do with making the glory. The glory and the shadow just happen to be located in the same direction — opposite the sun. The glory is made of sunlight scattered back toward you. It’s much smaller than a rainbow — and it’s made by light scattering from the larger droplets of a cloud, instead of falling raindrops. The glory is round — like the halo you sometimes see around the sun or moon — and it comes in muted rainbow colors.
Before the days of air travel, people sometimes spoke of glories they’d seen while mountain climbing. The same conditions — the sun behind and a cloud ahead — can also cast your shadow onto the mist. Then it’s possible to see a glory around the shadow of your own head.
If you enjoyed this show, the following articles may be of further interest to you:
- “Chasing Rainbows, ” Alistair Fraser, Weatherwise, December 1983, pp. 280-289.
- The Flying Circus of Physics, (1977). New York: John Wiley & Sons
From Craig Bohren:
“The glory is rather pastel in comparison with the best rainbows. In this context, I have a story to tell. My colleague, Alistair Fraser . . . was once asked by THE CANADIAN GEOGRAPHER (if I remember correctly) for a photograph of the glory. He sent his best photograph. It was never printed in the magazine on the grounds that the colors were too muted. Alistair wrote an irate letter pointing out that he was not responsible for the glories produced in nature, which, like it or not, do not meet the color standards of THE CANADIAN GEOGRAPHER.”
From The Flying Circus of Physics:
The glory results from light backscattered to its source by small particles whose radii are near or somewhat larger than the wavelength of visible light. The scattering is described by the Mie theory rather than the Rayleigh theory for smaller particles or by the normal reflection and refraction models for larger particles. The light that is returned in the direction of the light source enters a drop on an edge and exits from the edge on the opposite side of the drop after suffering both a reflection within the drop and skimmering along the drop’s surface. That skimming, which is described as being a surface wave, is not part of the standard wave optics used in modeling a rainbow. The return angles for different incident colors are slightly different and thereby produce the distinct colored rings around the shadow of the observer’s head. Since the angles involved in a particular pattern depend on the size of the drops, the colors are lost if the drops in the cloud have a large range of sizes.