Glories!
While looking out of the window on an airplane flight, I often see a circle of colors with the shadow of the airplane at its
center. Can you describe what this is? Beverly L.
When I was flying through clouds today, our plane's shadow in the clouds below had a circular rainbow tightly around it. It
wasn't just from one angle, and it was there for many miles. Why is that?
Ben, Buffalo, New York
 A glory seen
over Canada. Photo courtesy of Mila Zinkova and Wikipedia.
The phenomenon you saw is called a glory. We air travelers often see bright rings around the plane's shadow
whenever the plane flies in the sunshine above the clouds, if the sun is behind us. The sun must be behind us, like it is when we watch a
rainbow, so that cloud droplets can scatter the light into colors and bend them back to our eyes.
Most people see only one ring. The glory, however, can show many rings when the clouds are made of uniform water droplets.
Sometimes the rings fluctuate wildly in size. This happens when the plane skirts a canyon of clouds and its shadow comes and goes.
You ask why. We do not know. We can predict glories using a complicated mathematical model (the Mie theory); we can create glories
in the laboratory but we do not understand the physics behind the phenomenon.
Here's what we do know: The tiny drops of water found in clouds change the direction and amplitude of light waves passing through. The
size of cloud droplets is typically about 10 micrometers: the size of a red blood cell and ten times the wavelength of light. The angular
size of the glory (usually, less than 5 to 10 degrees across) depends on the size of the drops or crystals: the smaller the drops, the bigger
and fuzzier the rings. Glories polarize light, which implies their origin involves at least one reflection.
We think that glories are created like this: a droplet back-scatters light as the light goes around the droplet periphery. Each minute drop
shines uniformly with a ring of light. The glistening rings from the all the cloud droplets generate the glory.
Further Surfing:
Les Cowley: Atmospheric optics, glories--fantastic images
Glory image
from Les Cowley's Atmospheric Optics site
What causes a rainbow?
I
saw a lovely rainbow recently. The sky just inside the bow seemed brighter
than the sky outside the bow. Why?
How high do you have to be to see a full-circle rainbow?
How a full-circle rainbow looks
Why
are the colors in the second rainbow backwards?
What a rainbow looks like to a dinosaur, WonderQuest
(Answered Oct. 25, 2002, updated July 19, 2007)
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