From: pauld@exploratorium.edu
Date: Fri May 10 2002 - 15:00:04 PDT
Message-Id: <200205102200.g4AM00H06958@isaac.exploratorium.edu> From: pauld@exploratorium.edu Subject: Re: Shadow bands Date: Fri, 10 May 2002 15:00:00 US/Pacific
Hi Joyce
There are few photos of shadow bands, they are low contrast, moving bands which
are perfect for detection by human eyes and terrible for film. Perhaps someday
digital will get good enough to show them.
Go to a swimming pool look at the bottom on a sunny day. Notice the pattern of
light and dark on the bottom of the pool. The pattern is made by surface waves
that refract the light removing it from some places and adding it to others.
Next take a fish tank of water. Put white paper on the bottom. Hold a point light
source like a minimag light with the reflector removed over the fish tank. Now
pour in some clear sugar water notice the shadows on the bottom not from the
waves but from the changes in index of refraction in the liquid between pure
water and sugar water.
During the eclipse there are hot and cold regions of air, air at different
temperatures has different indices of refraction. It bends sunlight. It doesn't
bend it much however and usually the sun is so large (just 1/2 degree but large
enough) that the dark and light regions smear together so you can't see them.
However during the last phases of a total solar eclipse when the sun is 97%
covered it becomes a small enough source that you can see the shadow bands.
I hope this helps.
Paul D
> Hi Paul, I was a participant in TI last summer in the middle school program. I recently
showed parts of the solar eclipse web cast and in that you talk about shadow
bands. I had
students ask me what they were and I couldn't really give them an answer. Could
you help
me explain and also do you have a link to a picture of one?
>
> Thanks,
> Joyce de Flores
> Science Teacher
> Bristow Middle School
> (925)516-8720 ext 133
> jdeflores@brentwood.k12.ca.us
>
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