During a total solar eclipse, gradually changing snake-like "shadow bands" may be seen on the ground just before & after totality:pic.twitter.com/o34H8FAMbE
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integration over full disk does not; and (c) what sets the scale for the variation in illumination.
Presumably if I read the paper deeply I'd understand all that much better!
The comment about refraction can be put better: you can think of regions of turbulence as weird, tiny little lenses, bending light,
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