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This is an edit of a previous question. It has been edited so I can be more specific in my asking, as I'm still confused after looking at the answers to a similar question to my original. I have a very specific situation in mind, and I don't want to get something wrong that would make anyone with an atmospheric science background immediately cringe. Small market, I know, but it's important to me to be correct in this case. I'm looking to get as accurate an answer as I can, so I've added the "hard science" tag to this version:

A planet orbits a blue giant in a non-tidally-locked fashion. The planet itself has an average temperature just above freezing, and radius of 3000-ish km. The atmosphere is ~75% methane, is otherwise mostly water vapor/CO2, and only slightly less dense than Earth's. I'm imagining it as being dusty enough to resemble a blue-hued version of Titan when standing on its surface, with a high density of cobalt giving the dust a blue color. Does the sky appear blue in the sunset, or does Rayleigh scattering still make it look red? I'd imagine that the planet would look fairly blue looking down at it, and everything about it screams "deep blue sky", but I'm curious if there's something I'm not thinking of that would make the sky look anything other than blue.

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    $\begingroup$ Possible duplicate of Apparent Color of the Sun $\endgroup$
    – Aify
    Jul 3, 2016 at 0:18
  • $\begingroup$ This post-answer edit essentially makes for a new question... $\endgroup$
    – Bookeater
    Jul 4, 2016 at 4:19

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There are several factors involved, gas contents and density and stray elements all have influence.

Methane itself absorbs red and yields blue with a greenish cast by itself. Under sunlight methane forms an orange-reddish smog-like haze. The early Earth atmosphere DID have a high methane level once, and should have looked 'kind of' like Titan's current methane coloured sky:

enter image description here

References:
http://boards.straightdope.com/sdmb/showthread.php?t=534194
http://www.xenology.info/Xeno/5.4.2.htm
http://www.orionsarm.com/xcms.php?r=oa-page&page=gen_skyonalienworlds
https://www.reddit.com/r/askscience/comments/18hiem/what_color_were_earths_sky_and_oceans_prior_to/
http://www.space.com/16130-titan-landing-saturn-moon-huygens-pictures.html

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  • $\begingroup$ Under, say, a blue giant, would it be a blue-ish haze? And, purely speculatively, what would you guess the fog would look like under a white star? $\endgroup$
    – Viddog
    Jul 2, 2016 at 21:29
  • $\begingroup$ @Viddog It shouldn't be too hard to extrapolate from this answer, based on the spectral emissions of any particular type of star, to what such a world would look like orbiting some other type of star. Please don't assume that we'll do your work for you; instead, show your research and ask us to fill in the gaps! $\endgroup$
    – user
    Jul 2, 2016 at 22:29
  • $\begingroup$ @MichaelKjörling The problem is that I have a hard time wrapping my head around Rayleigh Scattering and the other elements that go into making an atmosphere the color that it is. Plus, while this answer is helpful, it's worth noting that Titan has a ~5% Methane concentration, which is about 15 times smaller than what I was curious about. I've no background in atmospheric science, let alone things that atmospheric scientists themselves get wrong (many of them didn't expect Mars to have a pink sky, but it does). I ask because I don't have time to learn an entire field to answer one question. $\endgroup$
    – Viddog
    Jul 3, 2016 at 20:28

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