Grand Canyon Bows
Primary and secondary rainbows captured from the South Rim by Brigitta Sipocz.
©Brigitta Sipocz, shown with permission.


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The brightest rainbow colours are produced by large raindrops, but not so large that they lose their sphericity.     Red light is refracted least and forms the largest rainbow.   Its light appears in the sky as a disk with a fairly sharp edge – only fairly sharp because the 0.5° angular size of the sun blurs it.   The disk dims away towards the bow’s centre.

Successive shorter wavelength colours have smaller and smaller disks.    The disks overlap and each colour except extreme red has mixed with it some longer wavelength hues.

At right are calculated rainbow intensity profiles for a few colours.    The lower full colour profile was made by computing profiles for hundreds of colours, weighting each by its spectral intensity at Earth’s surface and then adding them all together.   

Inside the bow, where the colours completely overlap, there is white light.    Brigitta’s two pictures show it also.