It may be that you recognize this acronym for the colors in the spectrum of visible light: red, orange, yellow, green, blue, indigo, violet. I learned it maybe 40 years ago as a backyard amateur astronomer.

Figure 1. Sunset, Nags Head, N.C. Photo: author.

This was a sunset photograph taken on 28 November 2019 while vacationing in Nags Head, North Carolina. I noticed the colors in the sky and I went to a balcony and shot this.

In the original, and to my eye, it was mostly just a bright red sunset, and that’s why I took the image. But back in our room, I edited it and played with the saturation and vibrance settings in the iPhone photos editor, and bang! out popped a spectrum.

The sun’s natural yellow color and the sky’s blue affect the colors here, and the clouds complicate things further by reflecting light. In a pure, real sunset, the shorter-wave light goes over the horizon first, as it is bent more by the atmosphere’s prismatic effect. So the spectrum here is spurious and reversed from a sunset (and a rainbow, for that matter). Red should be higher in the sky than the blues.

Green is missing, and this is a double misfortune for me, because in years of living on the coast in San Diego and consciously looking for it, I never managed to see the so-called ‘green flash’ which commonly (they say) occurs as the slender green part of the sun’s light gets preferentially refracted for a moment just after the sun has set over water.

Well, I’ll just say Roy Biv signed without his middle initial here.

Published by gsb03632

A college professor living in Scranton, PA

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