[at-l] Optical Phenomenon

[David Addleton]

the glory perhaps?

http://www.wonderquest.com/rainbow-circle.htm
*
Q: **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.

* Q: 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 R., Buffalo,
NY

*A: *The phenomenon you saw is called a glory.
Click<http://www.sundog.clara.co.uk/droplets/glorair.htm>for an image.
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<http://www.sundog.clara.co.uk/droplets/glorair.htm>

Seeing the whole-circle rainbow<http://www.wonderquest.com/rainbow-circle.htm>,
WonderQuest

 Why the second rainbow colors are
backwards<http://www.wonderquest.com/big-eyes-2nd-rainbow-neutron-star.htm>,
WonderQuest

 How rainbows form<http://www.wonderquest.com/rainbow-coffee-grounds-batteries.htm>,
WonderQuest

 What a rainbow looks like to a
dinosaur<http://www.wonderquest.com/reptiles-flu-gravitons.htm>,
WonderQuest

Why the * inside* of a rainbow is
bright<http://www.wonderquest.com/rainbows.htm>,
WonderQuest



On 3/16/07, Ginny & Jim Owen <spiritbear2k at hotmail.com> wrote:
>
> I have a question -
> Today as we drove down the highway near Datil, NM, just before sundown, we
> observed something neither of us has ever seen before.  It was a clear
> afternoon, not a cloud in the sky.  As we drove through the mountains, the
> sun fell behind a small peak.  Light from the sun shone all around the
> peak.
>   However the light wasn't white, or orange - it was a perfect round
> rainbow, circling the mountain.  As we drove on, the sun appeared in part,
> but the rainbow circle remained.  It was really quite cool.  A few minutes
> later we passed behind a ridge and when we went beyond it, the sun was
> again
> in the sky with a normal white light around it.  About ten minutes later
> the sun went down and there was a slight orangy sunset.
>
> So the question is, does anyone know what that kind of solar rainbow halo
> is
> called?  Has anyone seen one?
>
> Ginny
>
> PS - for CDT-l - there is snow in the hills near Pie Town ;-)
>
>
>
> -----------------------------------------------------------
> http://www.spiriteaglehome.com/
>
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