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   Zero Order Glow 

  Early evening rain shower.

There were bright primary and secondary rainbows opposite the sun.

Sunward, where fine rain was also falling, the sky was suffused by an intense orange. The sun was the same deep colour and had hazy blurred edges, the small inset image does not do it justice.

The unusual glow was caused by sunlight passing through raindrops without any internal reflection. Image©2003 Les Cowley.

Next time there is a rainbow look at the sky towards the sun. If rain is falling between you and the sun there will likely be an intense glow. It is best seen when the sun is low and already orange or red.

This extra glow, over and above the ordinary sky brightness in the sun's direction, is formed by light passing through the raindrops and emerging the other side without having been internally reflected. I call this the 'zero order glow' zero because the number of reflections involved is zero, glow because it is a diffuse light without the sharp intensity concentration of a rainbow's rim.