Re: pinhole small circular rainbow question

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From: Jon Christensen (jonnchristensen@yahoo.com)
Date: Tue Apr 22 2003 - 08:55:12 PDT 

Message-ID: <20030422155512.18024.qmail@web21306.mail.yahoo.com>
Date: Tue, 22 Apr 2003 08:55:12 -0700 (PDT)
From: Jon Christensen <jonnchristensen@yahoo.com>
Subject: Re: pinhole small circular rainbow question

Hi Debbie,

Don't worry, you don't need a new pair of glasses.

I have seen this small rainbow as well. I believe
that it is caused by the shadow of the airplane as it
is cast on the clouds below. The different
frequencies of light bend around the edges of the
airplane differently (I think blue bends the most, so
that color should be on the inside of the circular
rainbow you saw), causing a small roundish rainbow
around the edge of he shadow. We don't normally see
the rainbow around the edge of shadows because the
distance from the object causing the shadow to the
place that the shadow falls is too short for frequency
dispersion.

The dark spot of the shadow may not be noticed because
the clouds are reflecting the light evenly, so what
would be a dark spot, if the shadow was on the ground,
is partally illumidated by nearby portions of cloud
reflecting light.

Also, the white "projection screen" of the clouds
below reflects all of the colors very well. The green
or brown ground wouldn't do such a good job.

Hope that helps.
Can anyone verify my explanation?

Jon Christensen 

----
Physics Teacher
LWHS

--- Debbie Berlin <debbie_berlin@yahoo.com> wrote:
> 
> I was flying home to Boston yesterday and I noticed
> a rainbow outside the plane's window.  It was
> circular, which makes complete sense (I was viewing
> it above the clouds, thus against a white
> background, so I could perceive all of it).  Here's
> what I don't get.  It was much much smaller than a
> typical rainbow.  In diameter, it was about one fist
> held at arm's length.  I ruled out some obvious
> explanations but was then stuck.  Any answers? 
> Other than "get a new pair of glasses?"  :)
> 
> Thanks, Debbie
> 
> 
> 
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