There are several answers on this site and elsewhere about why the sky is blue and why sunsets are reddish. But I could not find anything that discusses the relationship between the blackbody spectrum and the spectrum of colors seen above the horizon after sunset.
In particular, the "physical spectrum" (meaning the set of colors seen in the sky at increasing altitude above the horizon) after sunset looks identical to the blackbody spectrum. Perhaps this is related to the fact that sunlight is approximately blackbody to begin with, but I can't find any source that discusses this. For example, consider the following questions:
If sunlight had an "even" spectrum in the visible range, instead of blackbody, would sunsets look considerably different? Would they stop looking like the blackbody spectrum?
Is the color spectrum at each fixed location in the sky actually a blackbody spectrum (whose color temperature varies with altitude), or only approximately a blackbody spectrum? (Assume even that the sun is a perfect blackbody.)
Since sunlight is blackbody, is it inevitable that any type of scattering would create a blackbody-like gradation of colors in the sky, i.e., not necessarily Rayleigh scattering?
In short, why does the physical spectrum of colors seen in the sky after sunset mimic the blackbody spectrum?