Purple Atmosphere?

[tituscicero]

After watching Star Trek 2009 I was left wondering why SciFi movies/shows very rarely show planets with a purple atmosphere. Wouldn't most "livable" planets be purple considering that most stars are red dwarves and red and blue makes purple :?: Our main sequence star produced white light does it not :?: And white light reflected upon the different elemental makeup of our atmosphere creates blue/azure.

Am I being too simple minded :?: Maybe what I am missing is the fact that there is no white light from a red dwarve and therefore the atmosphere is not blue and thus no mixture and no purple.

I want to see a purple earth like planet. It would be amazing :!:

 

[Saiph]

The color of an atmosphere depends upon the dust, molecules, and atomic content of said atmosphere. Our atmosphere is blue due to the way light scatters through it, and so for us, a 'livable' atmosphere will be blue, as it'll have similar composition. if you get into the reds and yellows you've got a lot of dust in the air..which is unhealthy. If you go with less blue...you've got a thinner atmosphere, also not good.

 

[tituscicero]

Thank you for the response. I think I failed to explain myself properly. I was not asking about what creates the color of the atmosphere since I know...I wiki'd it before posting. My question is basically: if we took earth (exactly the way it is) and put it around a red dwarf star would the color not be purple? I would think the red light would create a purple tone against the blue. My point was also since most star's in the universe are red dwarves and if earth like planets exist around red dwarves then most earth like planets we find may be purple. I like purple.

It really doesn't matter and obviously no one thinks this is interesting. Again, thanks for the reply.
:?

 

[CalliArcale]

Don't sell your thread short -- I think this is very interesting! I suspect folks haven't responded simply becuase they don't know either.

If you looked it up on wikipedia, you'll see that the atmosphere isn't really blue -- it appears that way because of light scattered in our atmosphere. So just adding red light won't turn it purple. Actually, purple does appear in our atmosphere at times. Pay attention at enough sunsets, especially when there's been a lot of particulate matter in the atmosphere to add some reds, such as after a volcanic eruption someplace upwind.

 

[nimbus]

Lots of pink hued skies in late afternoon skies of Arizona...

 

[3488]

I agree totally with Calli, do not sell yourself short tituscicero.

Saiph is correct regarding the Rayleigh scattering of sun light making Earth's skies blue (scattering of the blue end of the sun light in the atmosphere) & Mie scattering that makes Mars's skies pink & also Earth's skies redder or hazy (larger suspended particles scattering sunlight due to reflection from their surfaces).

Also as Saiph pointed out, darker skies would be due to thinner atmosphere.

Prior to Viking 1 landing on Mars in 1976, it was assumed the day time skies on Mars were either going to be very dark blue or even black due to Mars's pathetically thin atmosphere & the fact sunlight on Mars is only on average 44% as strong as on Earth (would also lead to darker skies).

It was a real surpirse to find that mars had bright skies & pinkish ones too. Later it was figured out that suspended dust iron oxide rich particles were reflecting sunlight causing a bright pink sky. Remove those particles, Mars will have a dark sky both day & night. Mars's atmosphere at the Geoid (average surface elevation) is the same density as Earth's atmosphere is at 30 KM / 19 miles above sea level.

That together with a 56% fainter sun than on Earth on average, would result in dark martian skies if the particles were removed.

Mercury will have dark daytime skies just like our Moon, due to lack of appreciable atmosphere. Venus has blue skies above the cloud deck, Jupiter, Saturn, Uranus & Neptune likely will also above theirs, though Uranus's & Neptune's are likely to be a very dark blue due to the Sun being so far away.

Andrew Brown.

 

[centsworth_II]

...Maybe what I am missing is the fact that there is no white light from a red dwarf and therefore the atmosphere is not blue and thus no mixture and no purple....

It looks like you didn't miss this fact after all.

The Earth's blue sky comes from the blue portion of light from the sun being scattered in the atmosphere. If there is little blue light available from a red dwarf for scattering, the sky will not be very blue. But there probably is still some blue light in a red dwarf spectrum and probably not as much pure red light as you might imagine. Also, the light level would be a lot lower, unless the planet was a lot closer the the red dwarf than the Earth is to the sun. So the sky would probably be a muted gray-pink. Maybe even a lavender... (almost purple ). All guesses on my part, assuming an Earth-like atmosphere.

 

[derekmcd]

I think the main issue here is differentiating between scattering and absorption.

 

[Saiph]

The effect of the primarily red light from a red dwarf star on an earthlike atmosphere, that scatters light to make blue light isn't as straightforward as mixing colors via a monitor.

The blue light from the atmosphere is due to scattering. What blue light the red dwarf puts out (while far less than the sun, is still there) will be scattered about the sky and come at the human eye from all angles. The end result is likely a fainter blue, due to less blue light in general.

The red light will pass through unscattered, on a direct line path UNLESS larger dust particles get in the way (or during sunsets). This means that you only see the red light from the dwarf if you look directly at it, or off of things that reflect the red light (the ground and objects). So your surroundings will have a very distinct reddish cast to them, the other colors being heavily muted.

One of the odd things about a red dwarf star is...it actually puts out less red light than the Sun! The reason it appears to be red is not due to how much red light it puts out, but that it puts out far less of the other colors so that red is the majority of what is emitted.

To elaborate; the sun puts out (making up numbers here!) 150 watts of blue, 200 yellow, and 150 red. This makes it appear fairly white (evenish color distribution) with an emphasis on yellow. A red dwarf star puts out 15 watts of blue, 20 yellow and 50 red. This makes it a distinctly red star...but still puts out less red than the sun.

 

[ZenGalacticore]

Our sky is appears blue because nitrogen scatters blue light in the visual spectrum. Air is mostly nitrogen. But on some world that say, manages(somehow) to have a greater proportion of oxygen in its atmosphere, the sky might appear greenish. IIRC, oxygen scatters green light. Too much O2, and there'd be no smoking allowed on said planet. :lol:

On a related note, I read that on some living planets, vegetation might appear red instead of green due to differences in star magnitude, color, and luminosity, or something other than chloraphyll making up the plant structures, something like that.

I'm sure that there are all kinds of chemical variations of planetary atmospheres combined with varying colors and intensities of stars that would create many different colored skies out there! I for one like the idea of a greenish atmosphere of a living exo-planet, it would appear very 'alien' to us.

 

[katzky]

♥ `Purple is the color of the year, that's Why maybe, the atmosphere just wanna be one of us...! :mrgreen:

surendettement

 

[silylene]

I fully understand that the conventional explanation of blue skies is the result of polarizable molecules in the atmosphere (ex: N2 and O2) scattering light according to a (lambda^-4) function (Rayleigh scattering). And this does happen.

An alternate explanation, which also does cause scattering, is that it is the result of microscopic (sub wavelength scale) density fluctuations in the atmosphere. Density fluctuations cause variations in local refractive index on a microscopic scale (sub wavelength scale). This causes scattering. There is a whole field of physical chemistry called fluctuation theory which among other things deals with the ramifications of stochastic effects of moleculr motion. The density variations are caused by the stochastic effects of individual air molecules moving around, so that the density at any given instant in a small enough volume is actually not constant.

There is still debate which is a more important factor for explaining blue skies: Rayleigh scattering or density fluctuation. Of course all the books reference one other, and give the simpler explanation of Rayleigh scattering i think mostly from a lack of diligence.

But truth is, both of these are factors in the (lambda^-4) scattering behavior.

Mie scattering is another light scattering source, dealing mostly with larger particles such as nanodusts and suspended aersols, which a posting above already explained.

 

[vogon13]

Had you evolved slightly different pigments in the photoreceptors in your eyes, the sky would already look purple.

 

[eburacum45]

There used to be a chart on the 'net somewhere showing the colours of a sky of a planet orbiting various kids of red dwarfs. The thing is, there is still quite a lot of blue in the light from all but the coolest red dwarfs, so the sky of most planets orbiting red dwarfs will also be blue. The colour saturation of the sky around cooler dwarfs is less, and the sky looks approximately white when all the nearly colours balance out at one point.

The very coolest dwarfs would produce a slightly pink sky on an Earth-like planet in orbit around them. Note that I'm quoting from memory- the chart is no longer available on the 'net.

 

[silylene]

Had you evolved slightly different pigments in the photoreceptors in your eyes, the sky would already look purple.

Quite true!

Every person perceives color differently. That is because the ratio of the number of cone cells for each of the 3 primary color receptors varies from individual to individual - by quite a lot (broad std deviations about the norm). And not at all infrequently, some individuals even comepletely lack one or more of the cone receptors and so cannot discern some colors.

Some animal species have 4, 5 or even 6 different color receptors, including receptors in the near IR, and in the UV (e.g honeybees), and can differentiate a much broader breadth of light wavelengths (color) than humans are capable, and with more precision in color determination. Some animal species can also see light polarization (honeybees again). We had a nice thread on this subject in the pre-Pluck SDC bio forum, now lost to history.

 

[MetalMario]

I belive that the creators of Star Trek, wanted to show people examples of what an Earth-Like planet could look like. Because our planet is blue, they decided to go with that one color. The Star Trek creators are a bit simple minded and know little about real space.