shadowbands1870large

Unfortunately there exist only few photos of the shadow bands world-wide. So there is often still published lithography of the shadow bands of the eclipse 1870-12-22 from Gela / Sicily (former Terranova) by Demetrio Emilio Diamilla Müller (see picture left, from: G.F. Chambers: The Story of Eclipses, 1900, Thanks to Michael Zeiler, click onto image for larger version).

The best theory for the emergence of the shadow bands is published by Codona 1986. His theory meanwhile accepted by the most scientists. Codonas scintillation theory is able to explain very well also subtle photoelectric observations .

After Codona the shadow bands at ground level result from interference of light rays, taking a somewhat different way in the atmosphere when crossing its turbulences and density variations .

The best observation conditions for such interferences can be expected from point light sources. On the other hand, the more extended the source of light is, the more less will such interferences be perceptible. Nevertheless you may observe the so-called ” heat waves ” on very hot days on homogeneous structured surfaces. In general, they are nothing different than the shadow bands.

During a solar eclipse however the solar crescent becomes more and more the shape of a slot. While a point light source would produce a spotted interference pattern, the pattern produced by this slit-shaped solar crescent is smeared to bands.

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