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, Dec. 10, 2009)

Comments

Readers' comments

• As a frequent airline passenger I have seen circular rainbows -"glories" - around the shadow of the plane. Recently I was amazed to see the same effect around the shadow of my head. I was walking along a levee by the river near my home in the North of England. It was a beautiful Autumn morning with mist lying low on the fields below the levee and the sun just coming up behind me. 
  Having read your explanation of the full circle rainbow I presume that I was in the right place at the right time with the cloud below me and the angles to be as you describe.
  Do you have other reports of this phenomenon at ground level? Peter, Leeds, UK 

  Reply:  Yes, Peter.  I have seen pictures of glories about the photographer's head.  The person was standing on the ground.  I can't seem to find one now, but here is a link to my article on glories.  If you track down the references under Further Surfing, you may find such an image. 
  http://www.weatherquesting.com/glory.htm

  Peter's answer:  Thank you, April.  Further Surfing did lead me to various photos of the Brocken Spectre Effect, which showed exactly what I had seen.  ...and I meant to add, that all the images on the web were taken from mountains. I suspect that I was especially lucky to set it at around 50 feet above sea level.
   

• I spent nearly fifty years as a professional pilot and I have long marveled at this phenomenon.  I was once told by a fellow pilot that these were "sun dogs" but now thanks to the internet, I know better.  The explanation is rather simple; the glory appears around the shadow of your airplane because that is the spot where your personal line of sight is between the sun and your shadow.  It's sort of like an eclipse of the sun.  You can see the same effect when flying at very low level when there are no clouds between you and the ground.  When you find the shadow of your airplane on the ground, you will find a bright halo of bright golden light around it.  I believe it is the rainbow and the bright ring indicates where the rays of the sun are parallel in relation to the size and positioning of the shadow, at least my friend tried to explain it to me and he was pretty smart, after all he went to the Naval Academy.  The effect is the same as a regular rainbow exce!
  pt that when you are on the ground, the bottom half of the rainbow is blocked by the earth itself.
    I became curious while converting my novel, "The Target; Love Death and Airline Deregulation" into a screenplay.  I wrote a scene where I described flying over a cloud deck at about five hundred knots where you get a true sense of high speed and being chased by your own glory adds to the thrill.  I suspected that I had misnamed it a "sun dog" in the book and on checking the net and your website, I found my error.  This will be corrected in the screenplay.
    I have long gloried in the "Glories I have been blessed to see and it is great to share the thrill with others.  I have a short tale about my greatest and rarest"Glory" if anyone would like to read it.
  Johnnie"U", Colorado Springs, Colorado, USA