Extraterrestrial sky color based on atmospheric composition and sun color

FtlIsAwesome

How can one determine the color of another planet's sky from its atmosphere composition and parent star color? Earth's atmosphere is blue for most of the day, then turns red at sunset. Mars is sort of the opposite: it has a red sky which turns to a bluish hue at sunset.

Until someone tells me otherwise, I assume that a human breathable atmosphere would have be a blue hue and not a different color such as green. I would certainly think its cool if other colored atmospheres can actually be breathed by humans.

FtlIsAwesome

Scratch that, it seems the atmosphere can have an inert gas other than nitrogen, which I assume will change its color.
http://www.physicsforums.com/showthread.php?t=470447

Radrook

Methane can cause a blue colored atmosphere. Mars' atmosphere tends to be redish because it is laden with rust (mineral limonite and magnetite). Magnetite reflects the limomite's reddish hue. The wind picks them up from the ground as dust and spreads them. The blue color seen in the first Mars photos was not the true color. The true color for most of the daytime was found to be butterscotch.

http://www.webexhibits.org/causesofcolor/14C.html

marcus

Ignoring the effect of colored dust, a plain gaseous atmosphere will tend to scatter blue more than red----will tend to scatter short wavelength more than long.

Light coming to you direct from the sun will tend to be reddened, by how much depending on how much atmosphere it has had to pass thru

Scattering removes blue preferentially and sends it off in random directions

So light rays from the sun that pass overhead, aimed at somebody above and behind us, get their blue removed and scattered randomly and some of it comes down to us and we see the sky as blue (because of that scattered light).

It would work with pretty much any gas molecule, I think. Anyway with a breathable atmosphere it should tend to be

"blue skies, smiling at me:
nothing but blue skies, do I see!"

---Ancient Broadway Tune

adoado

In computer graphics, a bit new trend is to physically simulate the sky, rather than using 'sky boxes' like what was previously done to get realistic skies. There are many prominent people in this field who have released papers, such as Nishita, etc.

Anyway, the point is that you could use these simulators and change the scattering coefficients, etc. to simulate different atmospheres. The scattering equations I would assume do not change from atmosphere to atmosphere (Rayleigh and Mie?) so you could easily find a simulator (or write one) and try changing the atmosphere coefficients and see what happens :)