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Shadow Bands
Often, when we walk in the sunshine, we can see the shadows of the atmospheric turbulence on the ground around us, or on our clothes. And the shadows move with the breezes. It's a little like what we see on the bottom of a swimming pool in the
sun. The water waves on the surface of the pool tend to focus the
sunlight to a pattern of dancing lines on the bottom. And the lines
move with the waves. Similarly, since the air around us is not all
of the same density, it too tends to focus the sunlight a little,
just a little. And although it is true that under ordinary circumstances
the shadows of the atmospheric turbulence on the ground are not conspicuous, still there is one circumstance where they are. At the time of a total eclipse of the Sun, just before and just after totality, these shadows become fairly conspicuous. Just before and just after totality, at the site of a solar eclipse, the Sun is seen as a slender crescent of light. Under these conditions, and only under these conditions, the shadows
of the atmospheric turbulence are seen with slit illumination. It
is this slit illumination that makes the shadows appear band-like
with the bands parallel to the solar crescent. It is these shadows
of the atmospheric turbulence, made linear by slit illumination that
are known to the astronomers as "shadow bands."
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