Reiterated: The sun produces the full spectrum of light (aka - white light [Red, Orange, Yellow, Green, Blue, [Indigo], Violet)- there may be a peak at some color, but it is not grossly predominant - yellow is at the center of our sensitivity). The unfettered full spectrum of light reaches our outer atmosphere. The atmosphere removes higher frequency light first (aka - violet, then blue, then green, etc.). The more atmosphere the light has to traverse before it gets to you, the more violet, blue, green, etc that is removed. Thus, for a sunset/sunrise, the light has to travel cross-ways through the atmosphere to get to you, so remove violet, blue, green, yellow, orange, and what’s left… red.
I think the sky on Mars has been proven to be reddish. ---------Because the planet is reddish I guess.
Shouldn’t the sky on Mars be blue, like on Earth, if most all the preceding posts are true?
Not so much “proven” as “we have photos.” As I recall, it was quite the surprise back in the Viking day.
Mars’ sky was expected to be dark blue to black. But, it turned out that the atmosphere is not thick enough to cause Raleigh scattering. The salmon pink colour is caused by suspended dust.
(To answer the OP, belatedly. If you follow Intelligent Design, the sky is blue because God wanted it to be blue. If you are a materialist, the sky is blue because of Raleigh scattering. Reasonable people can see that these are not mutually exclusive.) (Why yes, I did steal that from somewhere.)
While I’m sure it had something to do with Nationalistic teachings in Uni, I was always thought that the effect was due to Tyndall Scattering.
Rayleigh worked out the math but wasn’t the first to correctly explain why the sky is blue.
I absolutely agree, in my environmental chemistry class we did several experiments with liquid oxygen; It is the most perfect transparent sky blue color you will ever see outside the sky.
There are two questions here really, why is the sky bright and not dark like in space? And why is that brightness blue and not white like sunlight?
The answer to the first one is atmospheric dust scattering. Like headlights hitting a dirty windshield at night.
The answer to the second is above.
There’s only one problem with your theory. It’s wrong.
Diatomic oxygen only makes up slightly less than 21% of dry atmospheric gases. Diatomic nitrogen, at 78%, makes up the largest part of the gas, and argon is most of the rest, with other trace elements and compounds filling in the gap. “Wet” air will contain water vapor, i.e. dihydrogen monoxide in gaseous state, which will make the the sky appear pale and fuzzy. (This is why the sky on a cold, dry winter day, or in the desert, appears to be a much deeper blue.) The blue hue of the sky, as previously explained, is due to Rayleigh scattering. If you want a more complete explaination of that, check out any basic physics text. This isn’t some arcane, untested hypothesis; light scattering is an essential part of atmospheric optics and is used by visual astronomers and lens designers every day.
It’s also a band name.
So please, no disemenation of tin-foil-hat-ism’s here without a rational explanation based on known physics.
Stranger
I believe both reasons are at work here, I have quite a good physics and optics background myself and have no problem with the Rayleigh scattering causing shorter wave lengths to be reflected preferentially, but my whole point is that the color of a blue sky is exactly the same color of oxygen. I have never seen anything else that is such a perfect “sky blue” in nature. Air which is obviously about 78% clear nitrogen neither adds nor detracts from the oxygen color we observe.
I will agree with your theory, but until you have observed liquid oxygen for yourself and compared it to the color of an unpolluted sky don’t tell me I am wrong, the color match is far too close to be coincidental
The reason for the blue colour in liquid oxygen is due to the absorption of a photon of red light SIMULTANEOUSLY by two molecules of ground state (triplet) oxygen.
2 triplet oxygen + hv -> 2 singlet oxygen
In air at atmospheric pressure the chances of two oxygen molecules simultaneously getting a piece of action from a single photon are ‘bugger-all’.
Ok I capitulate, the Rayleighs have it. The perfect color match is completely chance. 
Thanks for the responses re. sunset/sunrise.
To further expand on that, here is a detailed explaination. Note: “This transition is not observed in small amounts of oxygen gas at low pressures due to the very low probability of this three-body process.”
And the sky is not one uniform hue of blue; it varies from pale blue-white at low altitudes and high humidity to an inky navy blue that mountaineers are familiar with. I’ll note that, on a clear day, when I look from Santa Monica Pier to Santa Catalina Island, it does not appear blue or blue-tinted. Nor do the land masses of Earth, as seen from space, appear to be tinted blue.
Feynman’s Lectures, Vol. I, Lect. 32, Pgs 6-9 have an extensive explaination of light scattering in the atmosphere:
…if we take the case of light in the air, we remember that for air the natural frequencies of the oscillators are higher than the frequency of the light that we use. This means that, to a first approximation, we can disregard [omega][sup]2[/sup] in the denominator, and we find that the scattering is proportional to the fourth power of the frequency. That is to say, light which is of higher frequency by, say, a factor of two, is sixteen times more intensly scattered, which is a quite sizable difference. This means that blue light, which has about twice the frequency of the reddish end of the spectrum, is scattered to a far greater extend than red light. Thus when we look at the sky it looks that glorious blue that we see all the time!
There are other aspects than alter the color of the sky, i.e. suspended particulates, absorption by ozone, et cetera, but dry atmospheric air at anything like STP is, for all intents and purposes, colorless.
I’m not clear on what your “good physics and optics background” is, MacGuyverInSeattle, but if you are going to mount a challenge against the conventional explaination, the theory of which is in wide application, you need to extend more than a “because I say so” qualification of you hypothesis.
Stranger
Why does everyone have to spell MacGyver with a u?
My background is a 6 year Chemical engineering degree and several years of optical design in very specific wavelenghts of ultraviolet, I have never spent much time investigating my observations so I give in, you are right, the earth’s land obviously does not appear blue from space http://www.btinternet.com/~fireballxl5/space/earth/ so that kills it. :rolleyes: