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I'm so sorry, but I find it mind boggling that someone takes the time to write up this semi-long article (it is well past the stub stage) and does not even mention the mechanism by which Rayleigh scattering works. I mean, sure, the formulas are nice to look at and so on, but a rough explanation of why that happens would, IMO, be one of the first things I'd want to add. I'll have a look in my text books later today and try to write something up.... 94.191.142.18 ( talk) 11:08, 2 December 2009 (UTC)
Would like to clean up all this blue sky stuff and archive most of this discussion any thoughts ? this page http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c2 has a good discussion to serve as a model Why is polarizability not included (is this the refractive index term ?) for instance, most forms of the equation include a alpha^2 term ( http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c2)
Although the lead paragraph mentions that Rayleigh scattering is for things smaller then the wavelength, I think some units would help people (eg light is about ~500 nanometers, molecules are about 1 nm, any visible particle is much larger then 500 nm)
Neither of these first two sentences actually says what Rayleigh scattering is. The first says that it's the reason why the sky is blue. (So, now we have a name to a scientific explanation, but not the explanation.) The second says that the scattering is dependent upon something or other, but we still haven't been told what it is that is so dependent! -- LMS
Has someone information about Rayleigh's "blue sky law"? -- looxix 21:57 Mar 18, 2003 (UTC)
The question is not answered very well. Why not green or another shade of blue? The answer seems more dependent on the absorption of energy and the re-emission of a photon from the oxygen molecules, which is blue. The emission spectrum of the other gasses that make up the atmosphere are outside of our personal visual range. Another interesting question is, was the color of the sky always blue? I think not, as the content of the atmosphere has not always contained the 20% oxygen.
The following paragraph (which was not written by me) I cut from the article, because its place is in the discussion.
The article is generally correct but light scattering depends on anisotropy. Anisotropy is the phenomenon where the speed of light in one direction is different in another direction usually perpendicular sources
Nitrogen, the major source of gas in the atmosphere is isotropic. However there are small quantum fluctuations in the isotropy of nitrogen where it becomes anisotropic. This microscopic fluctuating is actually the source of the scattering on which the Rayleigh scattering and theory is based. Any comments?
Synapse
18:43, 10 January 2006 (UTC)
>Dear Sir or Madam, > On that link to the Rayleigh scattering coefficient ks is a mistake in > the power of pi. Pi should be to the power of five and not to the power > of six. > http://en.wikipedia.org/wiki/Rayleigh_scattering > Please check this again. Thank you. > Best regards, Daniel Ploss
Can anyone find a reference to confirm this? -- Anon.
I found a different formula for the Rayleigh scattering coefficient. There the number of scatterers is in the denominator. It is from a lexicon of optics. I doubt that this is wrong. The formula is scattering coefficient b = (8*PI^3/3*N*lambda^4) * (n^2-1)^2, where N is the number of scatterers and n is the index of refraction.
Could you please give the source for the formula in the article. Thank you.
I also need the source for the intensity formula of Rayleigh scattering. Where was it taken from? 13:41, 4 Apr 2011 (UTC) —Preceding unsigned comment added by 87.77.200.134 ( talk)
Hi all. The formula in the article comes from "Atmospheric Chemistry and Physics", 2nd Edition, by Seinfeld and Pandis on page 696 of the hardcover edition. The formula is written differently, though, but it maths out to the formula in the article. Hope this is useful. I'll update the references section of the article to reflect this. 134.197.0.22 ( talk) 21:20, 9 January 2012 (UTC)
It should be mentioned that Raleigh Scattering is not physically a result of the size of the particles encountered by the light, but rather a result of interactions with the electron structure of the atoms (primarily a quantum mechanical interaction).
Simply put, the idea that size of particulate as being the primary physical reason for scattering in our atmosphere is no longer a modern view. This idea can't even be considered simplistic, because it is physically incorrect. While, Raleigh did observe the connection between scattering and size of the particle, this is not the reason for the scattering nor for why the sky is blue. Raleigh scattering is an easy to use formula and certainly important, however we shouldn't go too far - someone needs to explain that this effect does not consider light matter interaction as modernly viewed and that it posses Cretan inherent assumptions including the fact that spacing of particles is not considered. Application to atmospheric color should be amended to stress that the electronic structure of the particles, as governed by quantum mechanics (alternatively known as chemistry), describes the scattering of light in our atmosphere approximated by Raleigh Scattering.
Since no mention of where Raleigh's equations come from or when they are created are mentioned the reader is free to believe that his equations are modern and that the interpretation of them is the modern view. This is a serious oversight, because rule of thumb equations like this one often are often modified as theory develops. Lord Rayleigh's result was not fundamentally derived from more modern theory of quantum mechanics, which describe the interaction of light with matter.
Ultimately the question,"why is the sky blue?" is a matter of light - matter interaction, not light size interaction as this website asserts.
Furthermore, Raleigh's assumptions are not indicated here! How is the reader to know what circumstances his equation are valid for? I see no mention of pressure dependence which would effect spacing between molecules. Light when viewed as a wave must be considered to be able to diverge when passing through a gap on the order of a specific size, which would be effected by pressure.
The reason seems more clear in this link : Maybe we can incorporate it here ?? [2] Ap aravind ( talk) 09:05, 1 February 2010 (UTC)
You can't use terms from modern theory like "photon" in a document describing a theory that was developed prior for many reasons: 1. it creates ambiguity as to how modern the theory is 2. it suggests to the reader that the theory interprets light as photons, in fact the theory does not 3. it implies that the author at least heard the word photon before he died, this however is not possible
Simply put the use of the word photon in this context is confusing and erroneous. Consult any modern physics text book for confirmation. Suggestion (Tippler and Llewellyn).
So the smaller the diameter of the particle the less of the input beem goes out again. Particles of vanishing diameter would absorb all light, really big particles would emit more light than they receive.
What's wrong? 84.160.230.81 19:02, 5 October 2005 (UTC)
It would be very nice to have some "further reading", maybe some URLs or something like this about the S-Matrix.
I would like to see the extension to a complex index of refraction (ie, absorbing particles) included in the formula. My guess is that the only change is the add a absolute value inside the square.
192.249.47.9 ( talk) 16:15, 11 December 2008 (UTC)
would this also be the page to add something about Rayleigh's Criterion? i just learned about it in class, and came here to see if there was more information. it has to do with the angular separation of light sources and weather or not lenses can resolve the images of the two... here's a link to a page with more information on it ( http://www.fas.harvard.edu/~scdiroff/lds/LightOptics/RayleighsCriterion/RayleighsCriterion.html I wouldn't feel comfortable writing something myself on it seeing as I just learned about it.
The article is generally correct but light scattering depends on anisotropy. Anisotropy is the phenomenon where the speed of light in one direction is different in another direction usually perpendicular sources Nitrogen, the major source of gas in the atmosphere is isotropic. However there are small quantum fluctuations in the isotrpoy of nitrogen where it becomes anisotropic. This microscopic fluctuating is actually the source of the scattering on which the Rayleigh scattering and theory is based. Any comments?
This belongs in this section Daemon8666 20:23, 13 January 2006 (UTC)
I heard about the theory of Einstein and Smoluchowski, that describes scattering from density fluctuations on a local scale (with results similar to Rayleigh scattering) in media in which the scatterers are separated by distances small if compared with the wavelength of incident light. I didn't studied directly this E-S theory, but I found it in two texts about atmospheric optics. The first author uses E-S theory only for scattering in the middle region of atmosphere, which has higher density than the high atmosphere and reduces (by destructive interference) the effects of Rayleigh scattering. The second one states that E-S theory refers to matter that is taken to be continuous but with a refractive index which changes with position, and that Einstein didn't assume a discrete distribution of matter. For the moment I've no conclusion about that.-- Ran.olo 07:59, 21 August 2006 (UTC)
Does anybody know typical values for n and d in the atmosphere of Earth? Is the refractive index of the particle the same as that of air (approx. 1.0003 at sea level), or is a different value to be used for a single particle? In general, it would be nice if one could use the formula along with these values to make calculations with these. Getting information via Google about this seems to be very difficult (either the information is only about the principle but without numbers or it is drowning in details or you have to pay for it or Google's hit is about a completely different topic), so it would be nice if Wikipedia could provide such useful information. If I had such information I surely would add it to the article, but unfortunately I don't have any.-- SiriusB 20:24, 26 January 2006 (UTC)
The section "An explanation of Rayleigh scattering using the S-matrix" appears to have been written very casually. I am in favor of deleting it and taking a fresh start to add more theory, if it is needed. I deleted one error, but I think there are too many others to fix easily. David R. Ingham 21:26, 14 March 2006 (UTC)
I understand oxygen is blue. Why is this omitted from the discussion?
The answer to the above question is that the gas oxygen is not blue, it is colorless. Liquid oxygen is a pale blue color, which I have shown to my students on many occasions. Colors are frequently present in substances having an unpaired electron, as is paramagnetism. Even in the upper reaches of the atmosphere, the temperature is still not cold enough to liquify oxygen, and even if it were, there would not be enough oxygen molecules at that altitude to make any difference in the color. Therefore, the color of liquid oxygen is irrelevant to the discussion at hand. - Dr. Art
Where are the experimental measurements associated with the support of the grand boggling mathematics?
Some of us are wary of those who tend to "get lost in the mathematics".
"Logic is a systematic method for getting the wrong conclusion...
with confidence."
A scientist can never afford to discard data, however contradictory it may be to his ideas and intentions.
Edit: (Sometime around Wednesday, April 20, 2006)
My apologies for talking. I presented no data. I do not have access to the necessary spectroscopy equipment.
I wonder if there is any argument that ozone is blue.
I also wonder if there is any debate over why a gas flame is blue.
I also wonder if there is any debate over why there is some blue gas just beneath a candle flame.
I also wonder if a piece of white paper held a distance of approximately one kilometer is blue (one kilometer having about as many oxygen molecules in a path as two inches of liquid oxygen, which is generally agreed to be blue.)
I am eager to see the experimental measurements that support the theory of Rayleigh scattering. Coucilonscienceorg
Furthermore, what is the predicted intensity of color we would perceive from this scattering? How can it be explained that the blue of the sky matches the 500.7 nanometers of the strong emission line of doubly ionized oxygen? I see that there are references to evidence that the sky on Mars is blue. might that evidence can be shared with us? Coucilonscienceorg 08:50, 28 April 2006 (UTC)
I can not even begin to address the fundamental misconceptions presented in the previous comment. Anyway, now that that is out of the way, I cleaned up the s-matrix bit a fair amount, still needs a bit of proper prodding, but should be bordering on acceptable. -- Meawoppl 05:41, 18 April 2006 (UTC)
If the atmosphere of a planet contains atoms or molecules with particular emission spectra, will the sky of the planet be the color of the emission spectra, or the color of the scattering? Perhaps some of the excellent astronomers present can present some data in this regard. Coucilonscienceorg 09:48, 28 April 2006 (UTC)
Many who have posted in this discussion have mentioned the idea that spectroscopy is predicated on the idea that the change in energy state of electrons is the cause of photoelectric emission and absorption. This idea is extremely strongly supported by experimental evidence. Considering the lack of reference to any experimental evidence by the scattering hypothesizers, and the prevalence of accusation, off topic remarks, and other fallacious gestures, this whole discussion needs serious editing if it is to be considered a scientific discussion. In other words, the majority of people seem to like to believe that the sky is blue in honor of Mr. Rayleigh. At least the majority of people no longer think the world is flat. Too bad majority of people have no bearing in a scientific discussion where evidence is presented to support theory. When Edwin Hubble presented the idea that Universe is expanding, he had Marvin Humason's evidence presented immediately before hand. Only then did Einstein start to think that the cosmological constant was the greatest blunder of his life. Coucilonscienceorg 18:10, 17 June 2006 (UTC)
If Rayleigh scattering is the "main reason" for the blue of the sky, what are the other reasons? Why aren't these other reasons mentioned anywhere? Coucilonscienceorg 01:55, 1 May 2006 (UTC)
...there is only air above us. It may sound obvious to the point of stupidity, but it bears mentioning that there is no solid surface up there. When children look upwards on a bright sunny day, they see an apparent solid surface, and they hear it called by the name "sky." They wonder why this solid-looking "sky" thing is colored blue. Unfortunately most of us grow up without really grasping the idea that the "sky" is just a cloud of air being lit by sunlight from the side, with the black of space in the background. Or in other words, since there is no "sky," it's the air which has a blue color. Does my statement seem crazy? If so, this shows that at some level you believe in a "sky" which has color, while air does not. Rayleigh scattering explains why a miles-thick layer of air has a blue color. But Rayleigh scattering cannot explain the color of the sky, since "the sky" is an illusion. The bright blue stuff up there is called air, not sky. -- Wjbeaty 08:25, 15 June 2006 (UTC)
Okay smartass, but nobody asks the question "Why is the thick cloud of air above the earth incorrectly referred to as a sky (despite the fact that "sky" is a ludicrous and childish concept) tinted blue and not simply transparent?" —Preceding unsigned comment added by 164.92.175.76 ( talk) 16:13, 25 February 2008 (UTC)
when you look at a very distant dark object, a mountain for example, you see it blue. So, are you looking at the air or at a mountain made blue by air?
In the same way, when you look at the blue stuff above you, are you seen air or the dark interstellar empty space seen through the air?
You cannot see the blue of the air if you don't have a dark background...
And you can call "sky" the space made blue by the atmosphere.
it's only matter of point of wiew.
--
Ran.olo
12:52, 20 June 2006 (UTC)
Wjbeaty, I would say you are wrong because in the modern world we call "sky" as the atmosphere or gaseous molecules ABOVE us. If you referred back to history, you simply contradicted yourself. Okay back to your statement: "The concept known as "sky" derives from the Medieval concept of "heavenly firmament," a solid blue-colored dome above the Earth." I believe we all knew what the people were talking about rite? Well a solid blue-colored dome above the Earth to them is our gaseous atmosphere above us, so simply that means f(x)=y. A different concept might be = to another concept using different terms. If you're going to say math is not related to science well, it is related and also, as I said another concept can sometimes equal that concept. -- InternationalEducation 7:03P.M., 31 December 2006 (UTC)
If the sun's emission peaks at yellow, then why does it say that "there are more violet photons to scatter than there are blue ones"? Is this an error, or am I just misunderstanding the article? -- kier07 9:32, 30 July 2006 (UTC)
Sounds like an error to me. The most fundamental reasons for a non-violet sky are color perception, as well as the fact that there are far more blue photons than violet ones.
Also, I have no idea what a particular person further up on this page is babbling about. There is absolutely no fixed wavelength of blue light in the sky. The shade of blue varies with the amount of scattering taking place, and is not a constant 500.7 nm. It is a proven fact that the sky over highly populated areas is more of a light blue or even grey, due to the presence of more scattering particles in the air. So there's no exact match to emission lines of doubly ionized oxygen.
I'm baffled that anyone could believe the sky is blue because of the emission spectrum of oxygen (which implies that the sky is actually glowing due to photon emission as an electron drops to a lower energy level). This really has nothing to do with oxygen at all, as is evidenced by the blue color of the Martian sky when dust-free. 17:00, 31 July 2006 (UTC)
Sounds like an error also to me: visible spectrum of sunlight outside the earth's atmosphere has a maximum between 450 and 500 nm, i.e. in blue, so blue is the dominant sunlight wavelength scattered according to Rayleigh. But if we "add" Rayleigh's scattering law to sunlight spectrum we'll obtain a spectrum of scattered light that is not peaked in blue. Skylight contains light of all visible wavelenghts, but blue dominates in our color perception. --
Ran.olo
11:02, 20 August 2006 (UTC)
I find in this article that sky is reddened by sunset, but I don't think it really happens. I mean, sunlight is red at sunset (or sunrise) because it scatters a lot in the low atmosphere, so every object (e.g. clouds but also big molecules in the atmosphere, like dust) illuminated by (or seen through) this direct light will be red. But if I look up at the sky, I still see it blue, because it is coloured by the blue scattering that still dominates in the high parts of the atmosphere. So at sunset we have two different sources of light: direct, red light from the sun and scattered, blue light from the sky, and it explains why clouds at sunset are often pink (=red+blue).-- Ran.olo 22:04, 18 August 2006 (UTC)
ok, maybe it's another misunderstanding caused by word 'sky'... -- Ran.olo 19:48, 26 August 2006 (UTC) Ran.olo did you do a lab with food coloring in school because red and blue makes purple, maybe you could say red and white makes pink. InternationalEducation 7:11P.M., 31 December 2006
Red + blue DOES make "pink", actually magenta. This is additive color synthesis (superposition), which corresponds to experimental setup1: project 2 light beams, one blue, and one red, onto the same white surface. "food coloring", just like mixing paints, is substractive synthesis (removal by absorption), that is experimental setup2: project one single white light beam on a white surface after it has passed through 2 filters in a row, one blue one red. The only part of the light that was not absorbed by either one or the other filter will be purple. ( Mystero 80 15:21, 19 July 2007 (UTC))
I don't know why the bit on glaciers being blue keeps getting added to this article but the idea that glaciers are blue due to rayleigh scattering off of bubbles is totally dead wrong. Why is ice without bubbles just as blue as bubbly ice? The reason that ice is blue is the SAME REASON THAT WATER IS BLUE and that is the slight absorption of water in the far red region of the spectrum due to an overtone of the OH group stretch in the infrared region. Very simple, no bubbles needed. The bubble/rayleigh scattering thing is just a gross misconception. [4] -- Deglr6328 22:46, 23 August 2006 (UTC)
The section on why the sky is blue instead of violet seems to have some problems. In particular, it claims there is a rapid falloff in sensitivity below 450 nm, but this is clearly not supported by the graph, which shows that the S receptor peaks at 420 nm. The article formerly claimed that receptor peaked at 450 nm, but I have adjusted it to agree with the graph. It's clear from the graph that the eye's sensitivity to monochromatic violet light is not much less than its response to monochromatic blue light. The more likely explanation involves how the brain interprets the mixture of wavlengths present in skylight. An alternative version of this section is developing at Diffuse sky radiation. Perhaps that should be copied here?-- Srleffler 05:41, 5 September 2006 (UTC)
I was told it was because the violet light gets scattered again on its way from the sky down to you leaving the blue dominant. I make no guarantee that explanation is correct. Man with two legs 13:34, 9 October 2006 (UTC)
I'm TAing for a graduate chemistry class, and this is something that's always bugged me: Doesn't rayleigh scattering violate the conservation of momentum? I can't see how you can absorb a photon and reemit at the same frequency in another direction without transferring some momentum to another particle (thereby incurring an energy loss and frequency shift). Or is a molecule already in motion absorbing? But this would suggest that anisotropic materials exhibit less rayleigh scattering (and thus less absorbance), than materials with tons of molecular motion, which doesn't make sense to me.
Strictly speaking, in Rayleigh scattering the photon is not absorbed and reemitted, but regardless I think the answer to your question is that the momentum of the photon is very small compared to the momentum of the scattering particle. It's sort of like bouncing a billard ball off of a bowling ball. The momentum of the bowling ball is so large that any impulse (change in momentum) due to the interaction with the billard ball is insignificant. Optiksguy 19:37, 26 October 2006 (UTC)
In 1908 the Polish physicist Marian Smoluchowski became the first scientist to ascribe the phenomenon of critical opalescence to large density fluctuations. In 1920 Albert Einstein showed that the link between critical opalescence and Rayleigh scattering is quantitative. DFH 14:26, 17 November 2006 (UTC)
From the article: "...by particles much smaller than the wavelength of the light". Those particles are also inevitability smaller than green, yellow and red wavelengths, so why aren't them scattered as well?
Sorry for my English, I hope you understood me. Brass 08:27, 21 December 2006 (UTC)
They are scattered, but the angle is different. 86.138.101.53 01:56, 8 January 2007 (UTC)
Why does the sky turn green during a tornado? - Hamster2.0 02:11, 31 October 2007 (UTC)