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I've got a planet with a very special atmosphere. The properties are as follows:

  • Surface pressure = 0.7 atm
  • Composition:
    • 60% NO
    • 20% NO2
    • 10% N2O
    • 5% N2
    • 5% O2
    • traces of CO, CO2

My question is:

  • What would be the color of the sky/of the atmosphere?
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  • $\begingroup$ This page gives a good explanation of how to compute this. I'd write something up, but the calculations are much easier to implement in C++, and are perhaps best left for a programmer. $\endgroup$ – HDE 226868 Jun 5 '16 at 13:32
  • $\begingroup$ Would the 'sky' be visible from the surface? NO2 is a brown gas - it seems like that would severely limit your visibility. $\endgroup$ – cinnamon18 Jun 5 '16 at 14:56
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Since NO is generally thought of as a colorless gas, it would not have a direct color, but would generate a coloration through a similar process as our atmosphere (Rayleigh scattering). This process is based on the molecular size of the gas and is based on the wavelengths of the light (blue light has a shorter wavelength than red so is scattered less). NO molecules are similarly sized to our atmospheres major constituent N2 and O2. This would tend to produce a blue coloration. [This is a great simplification of the process.]

NO2 however does have a color, it is reddish brown (actually the leading contributor to smog coloration). This would limit your visibility through the atmosphere considerably producing a much hazier atmosphere and be a major contributor to coloration.

The combination of these sources should lead to an atmosphere in the dirty purplish coloration.

**I'm assuming a light source that is colorless, a redder or bluer star would change the color of the sky accordingly.

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