Ratio of Blue to Red Light: A Brief Increase Following Sunset

Science  31 Mar 1967:
Vol. 155, Issue 3770, pp. 1663-1665
DOI: 10.1126/science.155.3770.1663


Visible spectra of solar radiation were recorded during sunset. With the development of twilight, there was an expected decrease in the blue-to-red ratio; but directly upon setting of the sun there was a sharp rise in this ratio (due to the predominance of sky-light) which attenuated rapidly to follow the pattern that it had previously taken.