Water Aureole

Captured on a 'phone by Amanda Peters at Atlantic Wharf in Cardiff, Wales.

Light and dark rays appear to radiate outwards from the shadow of Amanda's head. It is also surrounded by a lighter halo. A "water aureole".

The dark and light rays are deep in the water.

Deeper still on the seabed itself we see bright dancing caustics.

Away from the shadow area the water surface reflects the sky to reveal gently undulating waves, the key to the aureole generation.

©Amanda Peters

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The waves refract incoming parallel sun rays to form caustic sheets - bright boundary surfaces of regions where the light rays cross and are concentrated. More about caustic sheets here.

The caustics are visible where they intersect the sea bed as dancing white lines.

They are also visible in slightly turbid water and then they can form a water aureole.
The caustic sheets are all roughly parallel to the incoming sun rays. When we look directly along them, the direction towards the shadow of our head, they appear by perspective to converge in the same way that railway tracks do in the distance.

The converging caustics give the opposite impression - that of rays and shadows radiating out from the shadow.

The rays look erratic and twisted because they are distorted by further refraction through the wavy surface.

A smoothly rounded wave forms a region of space below it where refracted sun rays cross. They cluster at its edges to form bright sheets of light.

The sheets join in a cusp at their top and spread apart below. .