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On
a December '02 afternoon an 8º high sun cast long sharp
shadows over a field of barley stubble, the remnants of harvesting.
A bright streak appears to slant upward at 11 o' clock from
the shadow of my head (actually from that of the camera which
marks the antisolar point).
The effect was subtle and more easily seen while walking.
This is an opposition effect "streak". The stubble approximates
to an array of parallel cylinders. When looking to the right or left
of the antisolar point their shadows are no longer hid and the field
therefore looks darker. But when looking up or down, the cylinders
still hide their own shadows (close-up
view) and so generate the bright streak. Image©Les
Cowley |
