Do standard atmospheres always have blue skies?

[Flynn]

Good Afternoon, All,

I know that, from a planet's surface, the color of the sky can look different than that of another world orbitting the same star. After all, Mars has a pinkish sky, while Earth's sky is blue.

I believe that the color of the sky is a combination of numerous factors, though probably most influenced by the chemical composition of the atmospher and the color of the star that is providing light to the world in question. I may be wrong here, but if I'm not, that leads me to my question below.

For Atmosphere Code 6, an atmosphere with a standard pressure and composition, which can support life without the need for a filter mask, will the sky always appear as blue? Even if it's shades of blue, will it always be blue?

Under what conditions would it not be blue? If it isn't blue, what kind of colors could we see in the daytime sky of a world with a standard Nitrogen-Oxygen atmosphere that humans can breathe unaided?

Hoping someone can satisfy my curiosity,
Flynn

 

[kafka47]

What is also a factor, is the hydrographic and soil composition, as part of the reason why Mars is pinkish is because of the landscape of the entire planet.

One could also see green depending on the chemical composition of the oceans or in an extreme case, which would probably make the atmosphere slightly tainted from Isodene, light purple.

 

[Anthony]

Actually, the skies of mars are pinkish because those are the color filters NASA is using.

The skies of an earthlike world might appear reddish for a planet orbiting a red dwarf, but are ordinarily going to be blue.

 

[Fritz_Brown]

That partly depends on how broad your "standard composition" definition is. Changing the chemicals/particulates present would change the refraction index and, hence, the colors. Also, the size of the world may make a difference - how large the "prism" is will determine which wavelengths get bent down to the surface.

 

[Flynn]

Andrew,

That teaches me to believe my eyes without looking at the source behind the images.

All,

The feedback seems so far to basically cover any color in the spectrum. Is that right? Are there any predominate color choices?

Thanks in advance,
Flynn

 

[Ptah]

Ahhh. The color of the sky, one of my favorite topics.

I believe the reason the sky of our colorless atmosphere appears blue from the surface is because of Rayleigh scattering. This has to do with the size of the scattering center. There is a preferential scattering of the blue end of the spectrum so the directly transmitted light appears more yellow or red, the scattered light appears more blue.

So for a standard atmosphere I'd say they'd appear blue. Thicker atmospheres will have a less intense color (because the light needs to travel through more air to reach your eye) and may have an even greenish tint as more blues and greens are scattered before they can reach your eye. The same star will appear redder in a thicker atmosphere than in a thiner atmosphere.

Most particulates are larger than the visible wavelength of light so they will isotopically scatter light of all visible wavelengths. If the amount of particulates increases, light sources travelling through them will appear redder than otherwise. As these paticulate distributions can shift, you might get beautiful changing colors, from pink to red such as can be seen in sunsets when there is a forest fire or lots of pollution.

Now to make it a little more complicated. The sky may appear violet if the star has more of this light in its spectrum (I have no idea off the top of my head what spectral classes might or could have this) and/or if you change the compoisition of the upper atmosphere. My suspicion is that if you did the latter so less violet is absorbed, you will also allow more UV to hit the surface.

Going a bit off topic, what of increased solar activity where the aurora becomes increasingly bright and descends to lower latitudes? The sky may still be blue but with these cascading, changing sheets of color that tint it.

Edit: Took out aerosols from with respect to particulates and added large particulates. The scattering depends on there size. If small around 200 nm still get alot of blue scattering, if larger 600-800 nm you will get the opposite effects from above, i.e., more red scattering and directly transmitted light appears blue and the scattered light is red.

 

[Ptah]

Originally posted by Flynn:
Andrew,

That teaches me to believe my eyes without looking at the source behind the images.

All,

The feedback seems so far to basically cover any color in the spectrum. Is that right? Are there any predominate color choices?

Thanks in advance,
Flynn

To not waffle...

Blue is predominant for a standard atmosphere, it will just vary in intensity with pressure.

For some special tainted atmospheres you could have a red sky and blue sun (even if type G star) if you have lots of just the right size particualtes and/or aerosols floating about.

 

[Fritz_Brown]

So, Flynn, are you asking us, "What color is the sky in your universe?"

 

[Spinward Scout]

From Ask Jeeves :

Why Is The Sky Blue?
The sun's rays hit the Earth's atmosphere, where the light is scattered by nitrogen and oxygen molecules in the air. The blue wavelength of this light is affected more than the red and green wavelengths, causing the surrounding air to appear blue. At sunset, the sun's light passes farther through the atmosphere, deflecting and decreasing the blue in the air. Scattering by dust particles and pollution in the air causes the sunset to appear red.

I think that's the official answer and here all this time, I thought the sky was blue from reflection of the oceans...

Dameon

 

[Flynn]

Originally posted by Fritz88:
So, Flynn, are you asking us, "What color is the sky in your universe?"

In a manner of speaking, yes.

Seriously, it was just one of those weird things that occurred to me, and not knowing the answer, I turned to the most educated group of people I know to find the answer.

Thanks To You All,
Flynn