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Dan wrote:
"Anyway, then I could measure with an accurate tape measure the height of the
line, measure the length of the shadow, and take some arctangents and get an
angle. If the line and length of shadow are long enough, serious accuracy
could be achieved, no? Anyone done this or see any obvious deficiencies in this
inexpensive method?"
The penumbra of the shadow will be a problem. Since the shadow edge is
"fuzzy", it would be difficult to be more accurate than a quarter of a degree in the
angle estimate. This is the same reason that sundials can't give local
apparent time to better than about one minute accuracy.
Speaking of the penumbra, here's a fun trick (which I have never seen in
print): Measure the width of the penumbra of a shadow cast by the Sun or the Moon.
The distance to the object casting that shadow is approximately 108 times
that shadow width. This can be very handy for estimating the distance to
buildings in a city (heights of buildings when the Sun is at high altitude). If you
walk along the edge of a shadow from a tall building and find that it's six feet
from complete shadow to complete sunlight, then the edge of the building
that's casting the shadow is about 650 feet away. Note that the shadow has to be
measured on a surface that is perpendicular to the light in at least one
direction but that's not hard to find in practice.
-FER
Frank R
[ ] Mystic, Connecticut
[ ] Chicago, Illinois
[X] in transit
