Talk:Rayleigh scattering

Rayleigh scattering (named after Lord Rayleigh) is the reason why the sky is blue. Rayleigh scattering of photons by Earth's atmosphere is dependant upon the size of the particles causing the scattering and the wavelength of the photon being scattered.

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

Have someone informations about Rayleigh's "blue sky law"? -- looxix 21:57 Mar 18, 2003 (UTC)

Why is Sky Blue? Answers

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.

From the mailing list

>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 changed it to to the 6th after some looking on Google. 69.142.2.68 10:51, 30 August 2005 (UTC)[reply]

The original reference for this article [1] has the "5" and "6" transposed between π and d. I've now re-written the maths from a solid reference, and I'm confident that it's now correct. The bottom two sections are still really chatty, though. -- DrBob 01:59, 31 August 2005 (UTC)[reply]

I found a different formula for Rayleigh scattering.

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.

Since that formula doesn't contain a term for the size of the particles (d in the article), it's probably only valid for the limit of d<<λ, so it's valid in a different domain. I'll try to check. -- DrBob 14:45, 11 Oct 2004 (UTC)

Could you please give the source for the formula in the article. Thank you.

Why is the Sky Blue?

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 (alternativly 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.

Confusion of Terminology

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 lewellen).