Talk:Diffuse sky radiation

From Wikipedia, the free encyclopedia

WikiProject Physics This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.
B This article has been rated as B-Class on the assessment scale.
High This article is on a subject of High importance within physics.

Help with this template This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.

This is taken from the excellent public domain NASA resource DICTIONARY OF TECHNICAL TERMS FOR AEROSPACE USE at http://roland.lerc.nasa.gov/~dglover/dictionary/content.html

Karada, are you sure this public domain material? -- looxix 00:04 Apr 18, 2003 (UTC)
It's USA government material. It's fine. HereToHelp 00:57, 28 September 2005 (UTC)

Contents

[edit] Merge with airglow

Can I suggest that instead of cleaning this article up, it is merged with the other sky background article (airglow)? Rnt20 06:48, 7 October 2005 (UTC)

[edit] Einstein and blue sky

The article claims that a relativistic correction is required to account for the blueness of the sky. I don't think this was shown anywhere in Einstein's work on scattering. Relativity has nothing to do with it. I am therefore removing the statement on the relativistic correction. DonSiano 18:15, 17 March 2006 (UTC)

[edit] Layman Question

If what is said is true, then why isn't the sky violet? This would seem to be correct, since the article says air scatters shorter-wavelength light in preference to longer-wavelengths. Matthew 00:17, 19 April 2006 (UTC)

Our perception of the color of the sky is based on how our brain processes the various short-wavelengths present in sunlight. There are multiple wavelengths present, but we only perceive a single color. The exact color of sky does not correspond to a specific wavelength. I am looking for a reference that can help explain the neuroscience of why the sky is blue. --Bjsamelsonjones 18:12, 29 June 2006 (UTC)

[edit] half-layman question

why isn't the sky ultraviolet, that is, transparent to us ? 86.104.188.234 17:39, 29 April 2006 (UTC) Stefan Udrea 17:45, 29 April 2006 (UTC)

seriously , I don't understand this:when the path of a light beam through the atmosphere is longer,the beams with higher energy (blue,violet,ultra-violet,etc.) should be scattered *less*, so they should get to our eyes, right ? while the beams of lower energy (red, orange) should be scattered more.It could be a stupid question, but nevertheless, I don't think anybody loses anything if the article gets more explanations. 86.104.188.234 17:43, 29 April 2006 (UTC) Stefan Udrea 17:44, 29 April 2006 (UTC)

[edit] Section moved from article

I moved the paragraph below here from the article. It doesn't seem to fit with the more common explanation of the blueness of the sky in terms of the wavelength dependence of Rayleigh scattering, as given in the article. If someone can adjust the text so that it's clear how these ideas fit together, this might be fine, but as it is it's just confusing.--Srleffler 15:27, 2 September 2006 (UTC)

Individual gas molecules are too small to scatter light effectively. However, in a gas, the molecules move more or less independently of each other, unlike in liquids and solids where the density is determined by the molecule's sizes. So the densities of gases, such as pure air, are subject to statistical fluctuations. Significant fluctuations are much more common on a small scale. It is mainly these density fluctuations on a small (tens of nanometers) scale that cause the sky to be blue.[citation needed]

I don't have a reference handy, but it is my understanding that this paragraph is the correct explanation. It could be better worded. Here's how it fits in: The sky is blue because of the wavelength dependence of Rayleigh scattering. Rayleigh scattering is the scattering of light off objects smaller than the wavelength. Those "objects" are the density fluctuations talked about in this paragraph. The individual atoms scatter light as well, but not enough to explain why the sky is so bright. Spiel496 16:37, 11 February 2007 (UTC)

I don't usually consider it essential to cite references for basic physics, because others can check my work. I this case I had other things to do and so, didn't explain my derivations and sources when questioned. Sorry to have caused inconvenience. I will provide convincing arguments if I have time.

[edit] The sky is purple?

Yeah ok. Before I believe this, someone ought to add some explanation for why a picture of the sky doesn't look purple. It looks like the exact same blue I perceive when I look at the real sky. If it is really a flaw with the human eye, then why in the world would a camera reproduce that flaw. I don't think that it does, which is why I dispute this until somebody clears this up. 8 November 2006 User:69.174.226.90

I agree, the physiological section does not benefit the article. It comes dangerously close to that meaningless sort of statement "it's really violet, but it looks blue". For an explanation to the "why not violet?" question, just look at the sky spectrum shown at the top of the article. It's a very broad peak centered at 500-550nm -- bluish-green. Perhaps the shorter violet wavelengths are absorbed, I don't know, but they aren't being lost in the eye. Spiel496 16:28, 11 February 2007 (UTC)
No one seems to have any defense of this section, so I removed it for the reasons above. Spiel496 06:28, 2 March 2007 (UTC)
Another idea: I don't think the violet rays are being lost in th eye. They are not emitted by the sun. The sun has it's peak emission at 500nm (Yellow) wavelengths, so these are naturally more scattered than the violet rays since there are more of them. Don't have any sources though, just simple physical intuition. User:132.229.227.66 10:45, 2 March 2007 (UTC)

[edit] Risk of skin cancer in the shade??

The included spectrum seems misleading, from the lengthy caveat: It was taken behind four panes of glass, so anything below 400nm is not shown.

My question is: if scattering is stronger for smaller wavelengths, wouldn't UV light be scattered most? If this is the case, I would think that it is important to present here if only to warn people of the danger of skin cancer being outside in a shady area. 121.44.119.136 21:32, 3 December 2007 (UTC)

[edit] Ocean emitting light?

I removed this line from the article because it doesn't make much sense. The ocean can appear blue because it's reflecting the sky. It almost makes it sound like the ocean itself emits light regularly. "This is partialy also because of the ocean and how deep it is making it appear blue on the surface whilst blue light is filtered into the atmosphere." Ghiles (talk) 06:02, 28 February 2008 (UTC)