Water Aureole ~ Seen by James Aikman looking into a reservoir in Glen A’Chroin near Callander, Central Scotland.

A rippling bright glow seems to radiate outwards from his head's shadow.

©James Aikman, shown with permission

An aureole needs a gently wavy surface and slightly turbid water so that light shining through it is visible.

The waves refract parallel sun rays to form caustic sheets. These are bright surfaces where the sun's rays cross and concentrate. More about caustic sheets.

Scattering from the turbid water particles make the causic sheets visible..

Caustics in clear water are only visible where they intersect the water bed.

The bright caustic sheets are roughly parallel to the incoming sun rays. Look along them towards the shadow of your head and they appear by perspective to converge (or radiate outwards). Railway tracks and crepuscular rays do the same.

The rays appear erratic and twisted because we see after more refraction by the wavy surface.

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Waves produce a region of space where refracted sun rays cross.

The rays cluster to form bright sheets of light. The sheets join in a cusp at their top and spread apart below.

This is quite different from conventional focusing.