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   Fogbow formation  



Fogbow light directions
. Light is refracted on entry. A
small proportion is internally reflected and then leaves from the side it entered. Diffraction effects dominate in small droplets and there are no well defined ray paths. Light is mostly directed 135-150° from its original path to form a broad circle of 30-45° radius around the antisolar point.
   
  
Fogbows form in the same way as rainbows. A small fraction of the light entering droplets is internally reflected once and emerges to form a large circle opposite the sun.

But... ...beyond that there are major differences. Rainbows are formed by raindrops which are so large that rays passing through them follow well defined 'geometrical optics' paths. Fogbows are formed by much smaller cloud and fog droplets which diffract light extensively.

The emergent light is mostly deviated 135 to 150° from its incident direction to produce the main fogbow of 30 - 45° radius centered on the antisolar point. The deviation corresponds roughly to the geometric optics angle of minimum deviation of ~138° for the 42° radius rainbow.

Fogbows are almost white with faint reds on the outside and blues inside. The colours are so washed out because the bow in each colour is very broad and the colours overlap.

Widely spaced supernumerary bows inside the main arc are produced by the constructive and destructive interference of overlapping wave crests along the main light path.**