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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:

Image 1

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?

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  • $\begingroup$ Cool question-look forward to reading the answer. This might help: physics.stackexchange.com/q/137189 $\endgroup$
    – user325452
    Commented Jun 6 at 15:18
  • $\begingroup$ This might interest the op: it is at least tangentially related and I found it informative. It has to do with how are eyes perceive color in the case of stars apparently (along with the typical emission spectra of stars. Stars tend to emit enough blue and red light alongside green that they appear white when registered by our RGB cones). discovermagazine.com/the-sciences/… $\endgroup$
    – user325452
    Commented Jun 6 at 16:43
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    $\begingroup$ Rayleigh scattering turns this into this. Neither path passes through green because the spectrum is a third path in chromaticity space. $\endgroup$
    – J.G.
    Commented Jun 6 at 18:28
  • $\begingroup$ @JosBergervoet I know that it can be at night.However it is way more less prominent that blue and red colors. $\endgroup$
    – Ishaan
    Commented Jun 7 at 7:11
  • $\begingroup$ Just the physiology.l of the eye. $\endgroup$
    – ProfRob
    Commented Jun 7 at 7:15

2 Answers 2

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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.

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We can see the green flash at sunset sometimes:

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

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  • $\begingroup$ I am aware of that phenomenon.However my primary concern was why is it so that green is way more less prominent in the sky than the other colors of the visible light spectrum? $\endgroup$
    – Ishaan
    Commented Jun 7 at 7:13

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