Interesting optical effect

"Kobra" wrote in message
...
This may be something different, but I saw this flying to Lake George two
weeks ago. I was about 1000' above the deck with the Sun high above me.
My
frontseat passenger keep saying a circular rainbow was following us and
that
the plane's shadow was in the middle of it.

All rainbows are circular. It just happens that when you are standing on
flat ground, you can't see the whole rainbow.

Since the center of any rainbow (all of which are circular) is a point on a
line projected from the light source through the viewer, the shadow of the
viewer (an airplane in your case) will always be smack in the center of the
rainbow, even if the viewer is moving.

For more sunlight effects, just look at your shadow on the ground at any
time during the day. Depending on the time of day and where your shadow is,
you'll see a variety of effects. My two favorite ones are the bright spot
with the shadow in the middle that you see on forested areas (due to the way
the trees reflect the sunlight, the reflection is brightest where the sun is
directly behind the viewer), and the moving blob of red you see when your
shadow is passing over a large parking lot (the taillight reflectors reflect
the sunlight back to you very brightly).

I told a friend of mine about it and he said that effect has a name. He
found it on the web and sent me this link:

http://www.touchingthelight.co.uk/features/brocken.htm

Low and behold...that is what we saw.

If you saw that, I'd suggest you were flying too low.

Seriously though, the effect described by the link you provided appears to
be specifically restricted to human shadows atop a shadow of terrain
(usually a peak), along with a rainbow. I wouldn't use the term they are
using to describe the similar thing viewed from aloft in an airplane.

Pete