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Below this question was left a comment linking to the Smarter Every Day video Space Station Transiting 2017 ECLIPSE, My Brain Stopped Working - Smarter Every Day 175.

At about 04:30 they show a short clip of a video recording of what looks like a white bed sheet hanging vertically and a shimmering pattern of light on it, I assume related to the total solar eclipse.

What's going on? What causes this? What's it called?

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These are called shadow bands.

As the sunlight is reduced to a very narrow strip, in the last few moments before totality, turbulence and refraction in the atmosphere will cause shimmering bands of light and shadow.

What you are seeing here is essentially the same as the twinkle that you see from stars.

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  • $\begingroup$ I see, thank you! fyi I've just asked Would an extremely bright star produce same kind of shadow band effect as seen in solar eclipses just before totality? $\endgroup$
    – uhoh
    Aug 4, 2018 at 16:19
  • $\begingroup$ @James K Is this explanation confirmed? I was under the impression that shadow bands were a few inches in size (I've never managed to see them in person) and that twinkling was more on the order of a meter or so. (It certainly seems reasonable otherwise.) $\endgroup$
    – Mark Olson
    Aug 4, 2018 at 16:27
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    $\begingroup$ Well read through the references in the linked wikipedia article. Balance of opinion is that no exceptional explanation is required, atmospheric turbulence is sufficient to explain the effect. $\endgroup$
    – James K
    Aug 4, 2018 at 21:00

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