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Patterns of Light in a Salt Water Pool
EPOD 2006-12-07
This picture showing a caustic network was taken in a natural salt water swimming pool near La Fajana, on La Palma (Canary Islands), Spain. An undulating surface of water acts like an arrangement of concave and convex lenses, causing an uneven brightness distribution at the bottom of a pool or even a shallow sea floor. The brighter blotches are in crude focus. The dispersion of water (the refractive index is different for different colors) is partially responsible for the observed color patterns—the height of the waves determines the focal length of the formed "lenses." This effect also causes the sometimes observed shadow bands during solar eclipses and is best seen when the water's depth is about 5 times the waves crest to crest distance.
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