Reflection rainbowsThe middle rainbow that is standing vertical…

Reflection rainbows

The middle rainbow that is standing vertical between the primary and secondary arcs is an unusual phenomenon, resulting from the sunlight shining as a beam upwards through the same water droplets that are refracting the primary solar rays after being reflected by the surface of the body of water (though wet sand can also produce this optical effect). These appear most often when the sun is low on the horizon at dawn or dusk when the water reflects the solar rays most powerfully, as evidenced in this case by the steep angle of the primary arc. The arcs and reflection bow will draw closer together as the sun sets lower in the sky before vanishing with it into the growing dusk.
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Loz

Image credit: Manolis Thravalos via EPOD
http://epod.usra.edu/
https://www.atoptics.co.uk/rainbows/reflect.htm