Can a planet with a dense atmosphere composed mainly of sulfur dioxide have a blue sky like Earth's due to Rayleigh scattering? Or would the composition change the color of the sky? I mean, it's well known that methane is responsible for the bluish colors of the atmospheres of the icy giants of the solar system, Uranus and Neptune, so it's logical to think that a planet with a significant amount of methane in its atmosphere would have a blue-green sky, would the same thing happen in a planet with a dense atmosphere of sulfur dioxide?

  • $\begingroup$ You got a good answer - but next time :-) consider that this is a physics or astronomy question and you're more likely to get good technical responses in those groups. Worldbuilding is pretty much exclusively for semi-fantasy world configurations. $\endgroup$ Jan 6 '20 at 18:44
  • $\begingroup$ @CarlWitthoft I thought it would be a good idea to ask this question in this group, since it's a hypothetical scenario and I have noticed that there are several experts on the subject here. Anyway, thanks for the suggestion. $\endgroup$
    – URIZEN
    Jan 7 '20 at 22:47

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Rayleigh Scattering is a universal physical process so it will always be involved when light passes through gases. Which is not to say it will always be the dominant determinant of the color of the sky. But in the case of an atmosphere composed of $SO_2$ that is doesn’t significantly absorb wavelengths shorter than 600 nm, Rayleigh scattering will dominate the color of the sky.

But the efficiency of scattering is proportional to the polarizability of the molecule. $N_2$ and $O_2$ have similar values ~1.6-1.7. $SO_2$ is 3.8

This means that longer wavelengths like green and will scatter more efficiently in your atmosphere than they do in Earth’s atmosphere.

I expect that your sky will be green near the star and then blue green then blues then to violets as you look to the horizon.

Table of Polarization Values for some gases. https://cccbdb.nist.gov/pollistx.asp#1977Mil/Bed:1

  • $\begingroup$ But CO2 is 2.5 and venus is yellowish? Must be traces of acidic cloud I think. $\endgroup$
    – user6760
    Jan 6 '20 at 4:39
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    $\begingroup$ The color of the planet outside the atmosphere doesn’t necessarily correlate to the color seen inside the atmosphere. @user6760 $\endgroup$
    – SRM
    Jan 6 '20 at 4:44
  • $\begingroup$ @user6760 I believe that sulphur/sulphuric acid in Venus's atmosphere is far more opaque than other gases in it, so that may be causing the dominant yellowish colour. $\endgroup$ Feb 25 '20 at 7:53
  • $\begingroup$ @SRM Take a look at mentallandscape.com/C_CatalogVenus.htm - in particular the section on Venera 11. That yellowish sky is seen from a lander within the atmosphere. $\endgroup$ Feb 25 '20 at 20:35
  • $\begingroup$ And also at web.archive.org/web/20151015045714/http://www.strykfoto.org/… $\endgroup$ Feb 25 '20 at 20:51

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