Explanation:
What is that white arch over the water?
What is being seen is a
fogbow,
a reflection of sunlight by water drops similar to a
rainbow but without the colors.
The fog itself is not confined to an
arch --
the fog is mostly transparent but relatively uniform.
The fogbow
shape is created by those drops with the best angle to divert
sunlight to the observer.
The fogbow's relative lack of colors are caused by the relatively
smaller water drops.
The drops active above are
so small
that the quantum mechanical wavelength of light becomes important and
smears out colors that would be created by larger
rainbow water drops acting like small
prisms reflecting sunlight.
The above striking image
of a fogbow
was taken last week with the Sun behind the photographer.
The rocks in the foreground are part of
Ocean Beach in California,
USA.
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