Re: Misconceptions assessments?

[William Beaty <billb@ESKIMO.COM>]

On Tue, 7 Nov 2000, Robert A Cohen wrote:

> > And, in fact, none of the answers
> > actually gives *the* "main" reason for the seasons.  The principal cause
> > of the seasons is the tilt of the earth's axis in space.
>
> I was attempting, albeit poorly, to force people to provide an explanation
> for why the tilt of the earth's axis in space is responsible for the
> seasons.  I've run across several people who state confidently that the
> cause is the tilt but cannot explain why (or explain that the tilt causes
> the hemisphere to be further in winter than in summer).

While trying to explain seasons to someone, I realized that the answer
isn't as cut and dried as we might think.  Shining a flashlight onto paper
from various angles does demonstrate the increased area covered by the
beam and the dimmer light per unit area.  However, the outside world is
not flat, it is covered by buildings and trees.  When the sun is low, it
shines on some angled surfaces more directly than it does in summer.
Also, the sun we see in the sky doesn't become much dimmer in the winter,
so why doesn't it heat the landscape as much?  How can we provide an
obvious, gut-level explanation of seasons to someone who lives in the
everyday world?

If we model the trees and buildings of the everyday world as a group of
hemispheres on a plane, the answer is clear.  When illumination comes from
an angle, the lighted portions are just as bright.  However, the regions
of shadow are larger than when the light comes from directly above.
Shadows cast by the sun are longer in the winter!  On average, the sun's
light is spread out over a larger region of land, but down here at the
"micro level" we see this as enlarged shadows, not as dimmer sunlight or
dimmer illumination of everyday surfaces.

       ____       ____       ____       ____
      /    \     /    \     /    \     /    \    light these from an angle
    /        \ /        \ /        \ /        \
   |          V          V          V          |


For some kids the flashlight on the Earth globe will be enough.  But for
others who need a less abstract explanation, appeals to the low sun and
the long shadows of winter might help.


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William J. Beaty                                  SCIENCE HOBBYIST website
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