Why can't we see green color in the sky?

Question

From sunrise to sunset we can see a variety of colors in the sky.

For example, during morning the most dominant color is blue whereas during sunset orange,red,yellow and there shades are more dominant. Other colors like indigo, violet etc are also visible to some extent.

We can also relate this to the visible light spectrum:

The colors in the right hand side are predominantly visible during morning while the colors in the left are visible during sunset. However, green is missing.

So my primary question is why all the other six colors (and their shades) can be seen in the sky but not the single color Green?

Answer 1

The sun acts like a black body radiator at $T\approx5500K$. Thus, its "natural" color is the superposition of all colours, which we experience as white. Rayleigh scattering is wavelength dependent, $\sigma \propto 1/\lambda^4$. It explains two well-known phenomena:

1. If the sun is just above the horizon there is "a lot" of atmosphere between the emitter (=sun) and the observer (=us). Hence, the "short" wavelengths components of the sun light have been scattered and the observers detects only the non-scattered photons. These are mostly red.
2. During the day, if the sun is over our head, the observer detects only those photons, which are scattered. As these are predominantly the "short" wavelength components the sky appears blue.

As green is in the center of the visible spectrum it is almost impossible to get the correct amount of scattering for a green sky. However, there is the so called green flash just after the sunset -- I linked some pictures. This is not a scattering effect, but a refraction effect.

Answer 2

We can see the green flash at sunset sometimes:

Image source: Brocken Inaglory via Wikimedia Commons, CC-BY-SA 3.0.