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Harald said ...
> - when seeing a rainbow in a storm that is NOT twinned, try to study
its
> roundness anyway. This cannot be done by photos, since wide-angle
lenses
> will distort the image. If we can discover rainbows that are sometimes
not
> round, we are one step closer to accepting that the twinned bow is due
to a
> distinct mix of oblate and round droplets.
One way might be to pay special attention in ANY rainbow to the gap
between
the primary and secondary bows. Photograph it in several positions
around
the bow.
While oblate drops only slightly affect the circularity of the primary,
the effect
on the secondary is greater because of the additional internal reflection.
The combined effect on the width of the gap between the two is worth
looking
for.
Attached is a simulation for oblate drops compressed just 3% in the
vertical
direction. The sun is 5º high - the simulation is in monochromatic light
for speed.
Look at the gap between the bows. The corollary is likely that
secondaries are
going to be rare when drops are non spherical because slight differences
in sphericity will blur them out to white sky.
Les
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