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I'm a sci-fi writer, and I have a question regarding a hypothetical planet that orbits an A-class or B-class Star.

Assuming Rayleigh Scattering occurs roughly the same way on this planet as it does on Earth, what colors would we see at Sunrise and Sunset?

I understand that what colours we see from our sun comes from the Rayleigh Scattering, but seeing as it's sci-fi I'm writing, I need a plausible colour scheme to use for my new planet. The Planet has a breathable atmosphere not too different to Earth, so for the sake of the argument, I'm assuming that the Rayleigh Scattering would occur roughly the same way, but my physics knowledge is sadly lacking in this area, and the Wikipedia article only refers to our own G-class Sun.

On that note, would the Sky still appear Blue, from an A-class or B-class Star? Or would the Rayleigh scattering trigger a completely different colour of the sky? Is there no 'right answer' when it comes to what sunrise/sunset/sky would look like on a distant planet?

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    $\begingroup$ If you can get a curve of the spectral output for your local star, compare it with the spectral output of Sol. Unless there's a complete lack of blue light, I'd imagine the daytime sky to be about the same color. $\endgroup$ – Carl Witthoft Feb 13 '14 at 12:43
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Followup to my comment: take a look at the table here http://hyperphysics.phy-astr.gsu.edu/hbase/starlog/staspe.html . Ignoring for the moment the spectral absorption lines, which shouldn't matter much to the Mark-I Human Eyeball, use the nominal temperatures of each star class in combination with the standard Planck distribution curves for a black body radiator, and that'll give you some idea.

Now, that said, the aforementioned eyeball is very good at doing color balance correction (which is why we perceive objects to have about the same color in broad daylight, near sunset, and under incandescent lamps), so it may turn out that the sky will just look "blue" even tho your A- or B- class star is a lot "bluer" than Sol.

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  • $\begingroup$ Thanks for your answer! My main question though, was about the colour of sunset/sunrise - the main events of my novel take place during evening/night/dawn, and I wanted to create a striking colour scheme to hammer home the juxtaposition between the new planet and Earth (my novel flicks back and forth between them). Also, sadly, most of that Physics is Greek to me, I understand the general concept, but you lost me somewhere around distribution curves, that just brought back way too many bad memories! o_O (That's why I'm a writer now not a scientist. :( ) $\endgroup$ – Singular1ty Feb 13 '14 at 22:12
  • $\begingroup$ @Singular1ty well heck, what with it being a different atmosphere, and probably a different ionosphere, go ahead and have any color sunset you want! $\endgroup$ – Carl Witthoft Feb 13 '14 at 22:59
  • $\begingroup$ Hm okay, thanks for your help then! I at least wanted to get a little grounding in the colorscheme, but admittedly sci-fi does give me a rather wide range of options. I just didn't want anything too unrealistic, so I'll stick with blues and purples I think. $\endgroup$ – Singular1ty Feb 13 '14 at 23:41

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