It’s not a unwillingness to provide a cite. The principles I’ve discussed are considered to be bedrock principles of modern physics. I’ve already mentioned Tyndall, Rayleigh and Compton. And Einstein and Planck. I don’t need to reference the respective papers. It’s textbook physics. (university texts - not children’s text). It’s not obscure physics. And I’m not making claims for the water buffalo population of Lake Victoria, without reference to publish research.
Dr. Strangelove, accused me of being at odds with every other source out there. In away, it’s like talking about Australia, and someone saying I’m the only one who believes it exists, and it isn’t on any maps anywhere.
I’m not even going to cite a textbook - the Wiki entries for Compton Scattering, Rayleigh Scattering etc are as good as any text book. Some Wiki answers of course are bad.
I’m not publishing a radical groundbreaking paper. And I don’t want to make any contentious statements.
I have had a few bad experiences.
But I will say something. The blue sky business, fully and properly understanding it, is a key to understanding a lot of physics. If you have any of the joins wrong, it can also mean you misunderstand a lot of physics. I’ve known physics post-grads who’ve had some of the joins wrong. But it’s wonderfully weird. It has plenty of the weird classical/quantum thing going on.
Just because you’re referencing “bedrock principles of modern physics” doesn’t mean they are the right ones.
“You know, I’m 40 today, but I don’t feel a day over 35.”
“Well, you’ve spent a fair amount of time on the 30th floor of a skyscraper, and one of the implications of relativity (a bedrock principle of modern physics) is that objects further from the center of mass of a large body will experience time dilation.”
Actually, if you look at the horizon you can see that the atmosphere does look blue. However, the bright surface of the Earth overwhelms the slight blue glow of the light scattering, so the blueness of the scattered light is not really detectable.
That disagrees with everything else on the topic. For instance, on the Tyndall Effect:
If you don’t like Wikipedia, here is a Georgia State Universitywebsite describing light scattering:
Also:
[QUOTE=jmrcm]
There is no lunar sky - something that is transparent by the grace of not being there is not black.
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“Sky” does not equal atmosphere. The “sky” is the expanse overhead. It includes any atmosphere, but also the “heavens” beyond, i.e. space and any astronomical bodies. The lunar surface does have a sky - it is black, not blue, because the lunar sky does not include an atmosphere, but there is still an expanse of space above the lunar surface that is visible.
[QUOTE=jmrcm]
The Tyndall effect (the blueness of milk and glass), Rayleigh and Compton scattering, they are all in principle the same thing.
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Arguable depending on how loosely you are using the words “in principle”. They are different enough that they have different terms named after different discoverers. They behave with different characteristics and the effects are calculated with different formulas.
[QUOTE=jmrcm]
If someone asks you why is the sky blue, if you respond that the light is scattered in all directions - and then you’re asked the question why is the sky white(gray) on a cloudy day - answering the light is scattered in all directions, is in fact more correct for a gray sky than a blue sky.
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From that GSU website above:
The key factor is that particle size in relation to the wavelength of light is crucial in determining whether the scattering will be directional or evenly dispersed. Rayleigh scattering is wavelength dependent (shorter wavelengths scatter more) but nondirectional (scatters evenly). Mie scattering is not wavelength dependent, but scattering is more directional. Tyndall scattering occurs from particles roughly the same size as the wavelength of the light, and is wavelength dependent. Again from wikipedia:
[QUOTE=jmrcm]
I’m not really sure what a Texan can or cannot understand, but if you can’t explain it to a Texan - or an example a great scientist who can’t remember the name of; an Oklahoman corn farmer, then you probably don’t understand it yourself.
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That comment was what is referred to as “a joke”.
[QUOTE=jmrcm]
Saying the blue portion of sunlight is scattered with greater intensity than the other wavelengths, is, completely and utterly wrong.
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And yet that is what the literature says. Again from wikipedia on Tyndall effect:
[QUOTE=jmrcm]
The blue portion of light is scattered with less intensity than other wavelengths. This is the fundamental principle of the Tyndall effect - why glass appears bluish.
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That is entirely backwards. The glass appears blue because the blue light is being scattered and is therefore eminating from the sides of the glass to travel to your eyes, whereas the main flow of light is emerging out the other side as determined by refraction.
[QUOTE=jmrcm]
How about, Arthur Compton. He won the 1927 Nobel Prize for Physics, for the Compton effect (it’s named after him). His paper was peer-reviewed, and his peer’s even nominated him for a Nobel, which he won.
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The Compton Effect does relate to X-ray scattering and shifting wavelengths, but that does not explain any connection to how the atmosphere scatters light. Compton scattering is described as “inelastic scattering”, versus Rayleigh and Tyndall scattering that are termed “elastic scattering”.
[QUOTE=jmrcm]
Your bluff has been called. There isn’t a single reputable modern physics book that will contradict me.
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So you dispute the Georgia State University website I cited?
[QUOTE=jmrcm]
So, under your principle (whatever you want to call it - did anyone ever win a Nobel for it?), blue light scatters more because it has a shorter wavelength then red, but X-rays scatter less because they have a shorter wavelength than blue light.
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You are misreading. He did not say that wavelength alone was the determining factor, rather the wavelength in relation to the size of the scattering particles. Blue light scatters more because it is about the same size, red light scatters less because it is longer wavelength, X-rays scatter less because they are much smaller.
This is just by way of advice, not a specific instruction. As you have already found, this approach is not going to work here. Unless you can cite something more specific than the “bedrock principles of modern physics,” you’re not going to make much headway on this site. This is a tough crowd - bald assertions aren’t going to convince them.
Based on what I’ve seen so far, this statement does not surprise me in the least.
Let’s see: Rayleigh scattering The strong wavelength dependence of the scattering (~λ^−4) means that shorter (blue) wavelengths are scattered more strongly than longer (red) wavelengths. This results in the indirect blue light coming from all regions of the sky. Rayleigh scattering is a good approximation of the manner in which light scattering occurs within various media for which scattering particles have a small size parameter.
To a first approximation, the Compton effect doesn’t apply to visible light. See an explanation here (problem 1). The Compton effect is much stronger with X-rays and gamma rays.
I don’t suppose you’re an advocate for “tired light” and a steady state universe instead of the Big Bang?
Out of curiosity, jmrcm, how do you explain a picture like this? As you can see, the transmitted light is orange, while the scattered light is blue. This is perfectly consistent with the idea that blue light is scattered more: the excess blue light that is scattered to the side is removed from the portion passing straight through, leaving only orange.
The picture is not consistent with your explanation, to the degree that you have even described it clearly. The scattered light is the same color of blue all the way to the left part of the stone, and yet the unscattered portion that hits the ground is a consistent orange. If instead the frequency was shifting as it scattered, we would see a color gradient across the image instead of a distinct split.
Actually, that makes me realize there is another fundamental problem with your explanation. If light in a sunset was reddish because it underwent a greater frequency shift due to passing through more atmosphere, then it must be the case that there was a larger number of atomic interactions. With each interaction, the path of the photon must change somewhat. Because of this, objects beyond the atmosphere should appear blurry. However, they don’t: they are perfectly clear, aside from the unrelated atmospheric refraction.
The standard scattering explanation has no problem with this, because most photons don’t interact with the atmosphere at all, and the ones that are transmitted pass through completely unperturbed. The scattered photons are completely randomized, but this adds only to an ambient glow and not a blurriness to the image.
Howdy, Marshal…We seen the same movies…I had a feeling you might show (which is why I left your line blank for you to write your own entrance)
I will abide by the rules.
There is no such thing as white light. What white light is, is the eye and the brain mixing colors in a certain way to give us the impression of whiteness. If you look at the diagram I have posted it has the visible spectrum with lowest energy(which is longest wavelength) on the left and blue to the right. If you saw all the visible spectrum at once, it would appear white. But if the entire spectrum lost some energy (through collisions, whatever) the spectrum would be moved left (more red) …That is why the sun appears yellow. If you have a light dimmer switch, you can observe that at low energy the tungsten filament is red, slowly turn the power up and it becomes whiter, if you can go higher, which most lights won’t let you, the tungsten filament will glow blue (you shouldn’t even look at this - you’ll see it with arc welding)
Every Photon in the universe is alike. Their only variation is in their energy, frequency, and wavelength - a photons energy is a function of its wavelength or frequency.
The only difference between a photon from the visible spectrum, and one that’s in the x-ray range, is its’ energy.
It means, you cannot have low scattering at a low frequency, and then high scattering at a higher frequency, but magically back to low scattering at an even higher frequency.
Not that I have sat down and rigorously worked it out. But, atmospheric density, distance from the sun, should effect the color of the sky. But this is a Straight Dope comment thread, not the Annals of Physic. I have a pet theory, that regardless of the planet you are on, the sky is mostly blue. (A pet theory, that would require a lot of pen and paper work, some tricky computer modeling, then spectrographic results from Mars. In other words, lots of work )
Color is just a phenomena that exists for humans. A single illumination, of a single wavelength of red, blue, green - like from a laser, we’ll see as a single color. Whites are more complicated - we need to see a specific distribution of wavelengths to see white.
That’s an absolutely false statement, aside from the fact that there’s nothing magical about it. Scattering is a very complex phenomenon with multiple sources, and these sources can most certainly combine to form a curve with a peak–or even many peaks. Even within the realm of Mie scattering alone, there are many local maxima.
MODERATOR COMMENT: jmrcm, that’s a comment that only a Moderator can make. If you think someone is being rude or insulting, the proper response is to report the post: click on the little red triangle with the !, in the upper right corner. Then let the Moderator handle it.
As it happens, I think that Dr Strangelove’s comment is slightly snarky, but not actually a direct insult. We want to have polite discussion here, without personal insults, but we don’t want to squash a sense of humor or a slight bit of “edge” (commonly called “snark”.) It’s often a fine line.
Yes, bodies emit radiation at different wavelengths based upon their temperature. I’m not sure how that is supposed to relate to the scattering of light that causes the sky to look blue.
Did you even read the second link Dr. Strangelove provided? It’s a .pdf, so I’ll copy the text for you.
You are still neglecting that the cause of the scattering is interaction with the air molecules, and thus the relationship of the wavelength to the size of the molecules affects the scattering process.
Ignore the stupid-ass Q in the title block. It was an accident. I tried to edit my post, but the buffer didn’t want to hold the post text. I didn’t feel like copy/paste and then recoding all the quote boxes and such.
The Feynman Lectures on Physics, Volume I, have now been put on the web (legally). Chapter 32-5, which I cited earlier, can be found here. Here is a slightly longer quote (but I still recommend reading the whole thing):
