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   Reflected Crepuscular Rays  

Rays pointing in two directions! Mouse over the image - the lower orange red rays point downwards to below the hill, the upper white rays point in a different direction to somewhere in the sky above the hill. Poul Jensen took this and other images on 1st September '06 looking towards Ester Dome from the Geophysical Institute at the University of Alaska, Fairbanks. The sun was 5° high and above the hill but hidden by cloud. What then produced the seemingly impossible lower rays? Image ©2006 Poul Jensen, shown with permission.

  Careful measurements of the images show that the upper short white rays from a hole in the clouds point towards the sun. The lower coloured rays have a focus below the skyline and ~5° below the astronomical horizon. Poul Jensen provided the explanation for their appearance. They are reflected light crepuscular rays. They are formed by upward going rays from the reflection of the low sun off a group of lakes 50-70km beyond the foreground hill and in the swampy Minto Flats Game Refuge.

Direct rays from the sun "a" penetrate a hole in the clouds to form the upper white rays in the image. Rays "b" reflected from the distant lakes appear to rise from a virtual sun below the horizon to form the lower orange rays. Not so improbable as it sounds because at that solar altitude, 70% or so of the incident light would be reflected upwards from a smooth lake. The reflected crepuscular rays will be partially polarised - something to look out for if you suspect that you see them. More reflected rays.