Reflection Caustics & Skypools. Image by Les Cowley June '09.

The dazzling sharp white patterns on the fishing boat hull are 'caustics' generated by sunlight reflected from the undulating sea surface.

Why are there well defined lines rather than fuzzy patches of light? Sun rays reflected from the surface cluster and cross to form sheets of light. Where the otherwise invisible caustic sheets intercept a surface like the boat hull they produce bright lines. The wave shapes produce paired sheets evidenced by the double lines on the hull with bright areas between them. More about caustica and their geometry here.

At lower right there are faint 'skypools'. Concave patches reflect the sky to towards the eye from their centres but reflect the harbour surroundings from their steeper edges. The result is oval patches of blue surrounded by the darker shore and boat colours.


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