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Blue Fire
2006-Jul-30, 09:23 PM
According to a LiveScience article, Phil got it only partially correct. This is the rest of the story, or at least More of the story. Check it out.
http://www.livescience.com/forcesofnature/050719_blue_sky.html
And a partial quote:

The sky is blue -- physicists tell us -- because blue light in the Sun's rays bends more than red light. But this extra bending, or scattering, applies just as much to violet light, so it is reasonable to ask why the sky isn't purple.

The answer, explained fully for the first time in a new scientific paper, is in the eye of the beholder.

"The traditional way that people teach this subject is that sunlight is scattered -- more so for shorter wavelengths than for longer ones," says Glenn Smith, an engineering professor at Georgia Tech. "The other half of the explanation is usually left out: how your eye perceives this spectrum."

While writing a physics textbook some years ago, Smith noticed that physiology usually gets short shrift, even though the spectrum of sky light -- when analyzed -- is about equal parts violet and blue.

Smith has written an article for the July issue of the American Journal of Physics that puts the physics of light together with the physiology of human vision.

"This is nothing that people who work with eyes haven't known for a long time," Smith told LiveScience. "I just had not seen it all in one place before."

The physical explanation for the blueness of the sky is attributed to the work of Lord Rayleigh in the 19th Century.

George
2006-Jul-31, 01:07 AM
I don't see anything that would warrant the claim, "the answer, explained fully for the first time in a new scientific paper, is in the eye of the beholder."

Perhaps the idea that violet plus blue yields blue as a metamer, maybe - not that I know better. It is well known, however, that color is determined from the spectral irradiance that enters the eye and the spectral response of the eye. There are other oddities regarding eye response, too.

Our response in violet is very weak and the sun's radiance is stronger in blue than violet, too. Further, the energy of each "violet" photon is higher than the others. This means that even if the level of intensity (wattage) for violet was the same as blue, the cones would register more blue since there would be more "blue" photons. It would not be a dramatic difference, however. The first two points are the key factors.

Lurker
2006-Jul-31, 01:30 AM
naw... Phil got it all wrong


Man in courtroom: "Why is the sky blue?"

Harry: "Because if it was green, we wouldn't know where to stop mowing."

I certainly hope that helps clear this little question up... :)

Blue Fire
2006-Jul-31, 01:46 AM
I don't see anything that would warrant the claim, "the answer, explained fully for the first time in a new scientific paper, is in the eye of the beholder."
I don't think I understand your comment here. What is it you are questioning? "...explained fully" , "for the first time", or "is in the eye of the beholder"? If you are taking issue with only the part of the article I quoted, I think the claim is warrented by the details in the rest of the article which I did not quote here.

George
2006-Jul-31, 03:40 AM
There was nothing new under the sun I found in the article with the exception of the metamer suggestion of adding violet to blue to obtain blue (that seems a little odd, but I may have misunderstood it).

There are several nit errors in the article,too. If you like I'll cover them, but I just happen to have a skunk in the back yard at the moment. My dog lost the battle, and its now my turn. I'm not kidding, either. :(

hhEb09'1
2006-Jul-31, 08:20 AM
I don't think I understand your comment here. What is it you are questioning? "It seems to me that it's like adding x-rays to the explanation--why violet instead of x-ray? We can't see x-rays either, their wavelength is even shorter than violet's. :)

George
2006-Jul-31, 01:55 PM
Yes. That is the issue and the point Smith may be conveying.

But, this is so well known, that I am surprised the article states that his paper is the first time anyone has presented the full picture. The response characteristics of the eye and the spectral irradiance of the sky, and the reason for it, have been known for a long time. If Smith's work is the first, we have been long overdue considering how much was already known. I did a Goo1 (level 1 Google search) and could not find a paper that incorporates all of this. Perhaps the originality claim is correct. I still doubt it.

About two years ago, or so, I read a related magazine article written by an astronomer who explained how the eye works and claimed the sun was really a green star. I was highly intrigued. Then came the BA's book, and I've been stuck chasing the sun's color ever since. I thought the article discussed the blue sky, too. If so, his work would have preceeded Smith's.

Dr Nigel
2006-Jul-31, 08:35 PM
We do see "violet" light, but it activates only our blue-sensitive cones (and not as strongly as does blue light). Sky-blue light also activates our green-sensitive cones very slightly. What we see as sky-blue contains a little bit of green (but only in the way we perceive it).

You know how the sky has different shades of blue? Well, a part of that is determined by differences in the spectrum of light that actually enters our eye. Where the sky is an intense, deep blue, that is mostly the shorter-wavelength stuff. Where it looks a bit less intense (and not just the "washing-out" effect caused by looking through more atmosphere, as the sky overhead can appear different shades of blue at different times of day and on different days), there are some slightly longer "blue" wavelengths involved as well.

This has been known for decades, so I do not quite see what this new discovery is meant to be.

Anyway, I thought there were two effects at work - one scattering (absorption / re-emission at different intensities for different wavelengths) and one refractive.

George
2006-Jul-31, 08:48 PM
We do see "violet" light, but it activates only our blue-sensitive cones (and not as strongly as does blue light). Sky-blue light also activates our green-sensitive cones very slightly. What we see as sky-blue contains a little bit of green (but only in the way we perceive it).
Yes, perhaps it's time for a graph of our responses (http://www.ndt-ed.org/educationResources/CommunityCollege/PenetrantTest/Introduction/lightresponse.htm) of our three types of cones. [The blue end coloring looks correctly aligned to wavelength to me, but not the red end.]

[Added: notice how insensitive our cones are to violet.]


You know how the sky has different shades of blue? Well, a part of that is determined by differences in the spectrum of light that actually enters our eye. Where the sky is an intense, deep blue, that is mostly the shorter-wavelength stuff. Where it looks a bit less intense (and not just the "washing-out" effect caused by looking through more atmosphere, as the sky overhead can appear different shades of blue at different times of day and on different days), there are some slightly longer "blue" wavelengths involved as well.
I do not quite follow this. Are you saying a little more green exists overhead at certain times of the day to cause blue to lighten, regardless of other effects? That makes some sense near noon time, I suppose.


Anyway, I thought there were two effects at work - one scattering (absorption / re-emission at different intensities for different wavelengths) and one refractive. How do you see refraction contributing?

grant hutchison
2006-Aug-01, 11:22 AM
There was nothing new under the sun I found in the article with the exception of the metamer suggestion of adding violet to blue to obtain blue (that seems a little odd, but I may have misunderstood it).Indeed. The whole story has been around for a long time, and is covered as such in many standard textbooks. Craig Bohren (http://homepages.wmich.edu/~korista/atmospheric_optics.pdf) gives a succinct summary (Section 2:3 in the linked article, including mention of metamerism). John Naylor addresses the eye's sensitivity as it affects the blueness of the sky in Out of the Blue, as does Marcel Minnaert in Light and Color in the Outdoors: and those are just the first three reference sources I lifted off the shelf.

Indeed, Phil seems to have done more background research than Glenn Smith, since in his section on the blue sky (Chapter 4) he explains why the sky doesn't appear violet, and mentions that: "... your eye is more sensitive to blue light than it is to violet."

I can only guess that Smith restricted his browsing to basic physics texts, which were trying to teach about scattering, rather than specifically about the blue sky.

Grant Hutchison

George
2006-Aug-01, 01:06 PM
You must show us a picture of your library someday. :)

Arnold Bussick's (http://www.i2o.uva.nl/BGB/KIN/essay_bussink.pdf) paper was written about a year earlier than Smith's covering the eye's response contribution and light scattering, even Einstein's Critical Opalescence approach was briefly introduced.

The hype of being first, of course, might not be Smith's fault.

Blue Fire
2006-Aug-01, 02:20 PM
Indeed. The whole story has been around for a long time, and is covered as such in many standard textbooks. . . .

Indeed, Phil seems to have done more background research than Glenn Smith, since in his section on the blue sky (Chapter 4) he explains why the sky doesn't appear violet, and mentions that: "... your eye is more sensitive to blue light than it is to violet."

Grant Hutchison
Okay, guys, Thanks for all your responses and information re my original post here! Much appreciated. I was not aware Phil had indeed covered this in his book. I haven't read it. I made the incorrect assumption (hunh, imagine that!) that since the issue of metamers and how the eye percieves different wavelengths of light wasn't mentioned in his article in the Misconceptions page of this site, that perhaps he hadn't been comprehensive enough.

Live and learn! Thanks again to all! Hopefully I will continue to live some more and learn some more,... and not make those annoying assumptions as often - I don't figure I can eliminate them altogether. :)

George
2006-Aug-01, 04:46 PM
Live and learn! Thanks again to all! Hopefully I will continue to live some more and learn some more,... and not make those annoying assumptions as often - I don't figure I can eliminate them altogether. :)
I think you'll find we all enjoyed it. So, thanks. The media(?) claim that the article was a first is "bad astronomy" and that is what we go after, of course. :) We've had some interesting colorful conversations regarding this topic; I'm sure we'll have more.

Gillianren
2006-Aug-01, 07:40 PM
Okay, guys, Thanks for all your responses and information re my original post here! Much appreciated. I was not aware Phil had indeed covered this in his book. I haven't read it. I made the incorrect assumption (hunh, imagine that!) that since the issue of metamers and how the eye percieves different wavelengths of light wasn't mentioned in his article in the Misconceptions page of this site, that perhaps he hadn't been comprehensive enough.

Well, now, you have to read the book to make up for it, don't you think? It's only polite!

George
2006-Aug-01, 09:18 PM
Metaphorical gold is another subject. ;)

jkmccrann
2006-Dec-02, 05:28 PM
Interesting discussion here, but the first thing that comes to my mind is - we may well see the sky as blue, but how about our animal neighbours we share this place with?

How do they see the sky? Insects for instance, is it a blue expanse they glimpse, or some sort of yellow wonder? Or is it in various shades of gray?

It would be interesting to know how other animals perceive the most common sight on the planet.

George
2006-Dec-02, 10:09 PM
You can Google for quite a variety of information regarding animal vision.

Surprisingly, birds, for one, have four types of color cones compared to our three. Also surprisingly, for what little I've seen, these color cones have sensitivies independent of each other. In other words, each wavelength of light can only be detected by one of their cones, not more than one. This gives them much better input for their color processing. My guess is they see many colorful objects slightly different but probably with greater vividness.

Deer, at least whitetail, have only two color cones, but they have larger eyes with other special features to enhance vision. One color cone may even allow vision in the near UV range. After learning this, I think of how funny it is that deer hunters think they are able to climb in deer blinds unnoticed by the deer because they, the hunters, think the sky is dark, but to the deer, the sky is relatively bright. :)

hhEb09'1
2006-Dec-04, 04:26 PM
After learning this, I think of how funny it is that deer hunters think they are able to climb in deer blinds unnoticed by the deer because they, the hunters, think the sky is dark, but to the deer, the sky is relatively bright. I didn't know that was what deer hunters thought, I thought they climbed up to the blinds because deer didn't notice them up there. :)

George
2006-Dec-04, 05:16 PM
That is true but they assume that since it is dark when they climb up, then the deer can't see them. I am a hunter and always assumed we risked injury, freezing, and snake bites for that purpose. :rolleyes:

IIRC, deer can not see orange or light of greater wavelength, so although hunters now wear orange primarily because they don't want to get shot by other hunters, I think many hunters also think the deer can't see them. Yet, any object the eye can not see will look black, so a deer will see hunters as if they were wearing black, which could stand out like a sore thumb.

hhEb09'1
2006-Dec-04, 05:33 PM
I think many hunters also think the deer can't see them. I've never heard this theory before. All the hunters I've ever talked to, always assumed that the deer was almost certain to be able to see them. :)

George
2006-Dec-04, 05:39 PM
You know too many realists. :) Me and the boys, on the other hand, strive to see ourselves as being much more clever than we really are. :)

maryccc
2007-Jan-03, 06:17 PM
So why is the sky blue?

George
2007-Jan-03, 09:03 PM
The sun strongly produces photons that react to our eyes. The higher energy ones are on the blue and violet end and the photons with less energy are on the red end of the color spectrum (violet, blue, green, yellow, orange, then red).

Our atmosphere, especially nitrogen and oxygen which is the bulk of the composition of the atmosphere, will scatter these photons in a special way. The blue photons will scatter about 6 times more than the red photons. Thus, blue light (photons) will reach your eyes much more often (6x more often) than the red ones.

This is called Rayleigh Scattering and the amount of scattering between any two frequencies of light varies as the fourth power of their ratio. Blue is around 450 nanometers in wavelength and the far red end is around 700 nm or so.

That is the short answer. For a little deeper look...

All the above assumes that the number of photons entering the atmosphere from the sun are all equal in number for each color. This is not the case. Surprisingly, the peak of the sun's output is in the blue portion of the spectrum, not the yellow or other color. The intensity of the blue light production from the sun (@ 450nm) is almost 50% greater than the amount of red light (@ 700nm) produced. So this gives blue light an even greater advantage.

That would be close to the end of the story for the blue sky if it weren't for the fact that the 50% value I just gave is for total energy and not number of photons. Since blue photons carry more energy than red ones, then, for example, if there was an equal amount of energy for both colors, there will be more red ones than blue ones. Is it confusing yet? The equation is E=hf [f is the frequency].

As it turns out, and I think I am correct, the 50% gain mentioned by the blue photons is lost because of this fact and the net result is back to about 6 blue photons to every red photon that your eye will see coming from the portion of the sky that is away from the sun.

There are several other threads which can help if you search or would like me to point you to them.

ArgoNavis
2007-Jan-03, 09:09 PM
So why is the sky blue?

Rayleigh scattering - the atmosphere is composed of particles that are just the right size to scatter blue light out of the coloured spectum of the Sun, leaving the Sun with a yellow tinge.

and of course, the white light of the Sun is composed of a spectrum of visible colours from red-orange-yellow-green-blue-indigo-violet.

Kristophe
2007-Jan-04, 11:02 PM
Interesting discussion here, but the first thing that comes to my mind is - we may well see the sky as blue, but how about our animal neighbours we share this place with?

How do they see the sky? Insects for instance, is it a blue expanse they glimpse, or some sort of yellow wonder? Or is it in various shades of gray?

It would be interesting to know how other animals perceive the most common sight on the planet.

They'll all see it as either blue, or as a shade of grey, depending on how their eyes are made up. Blue is just a waveband of light. How their brain interprets those wavelengths in a visual picture, though, probably isn't knowable. I don't think we can know even how other humans interpret the colours.

George
2007-Jan-04, 11:57 PM
maryccc, please notice Kristophe's avatar. It is a section of the northern hemisphere of Saturn and is probably close to true color. It is blue because the atmosphere there is nearly free of clouds which allows for sunlight to scatter.

ArgoNavis
2007-Jan-05, 02:32 AM
maryccc, please notice Kristophe's avatar. It is a section of the northern hemisphere of Saturn and is probably close to true color. It is blue because the atmosphere there is nearly free of clouds which allows for sunlight to scatter.

That avatar image looks more like the rings of Saturn rather than the disk.

and Saturn looks orange/yellow through a telescope, same with voyager images. Something to do with the ammonia in the atmosphere i thought.

I suspect that avatar is a false colour image of the rings.

maryccc
2007-Jan-05, 02:45 AM
I'm not totally sure I understand. I can see why now my dad said I don't know when I asked him years ago the same question. So is it scattering of light that make the colors? And the atomosphere determines the colors? Why is Jupiter Orange?

George
2007-Jan-05, 03:59 AM
That avatar image looks more like the rings of Saturn rather than the disk.
It does look that way but those are the shadows of the rings cast upon Saturn.

APOD (http://antwrp.gsfc.nasa.gov/apod/ap050211.html) gives a better view and a description.

I don't think there is any explanation why the northern hemisphere has such little cloud structure, but it does produce a nice shade of blue. Hmmmm... maybe planetchromolgoy should be an integral study with the sun's color. ;)

ArgoNavis
2007-Jan-05, 09:09 AM
I'm not totally sure I understand. I can see why now my dad said I don't know when I asked him years ago the same question. So is it scattering of light that make the colors? And the atomosphere determines the colors? Why is Jupiter Orange?


Jupiters colours are explained rather concisely here:

http://antwrp.gsfc.nasa.gov/apod/ap960803.html

ArgoNavis
2007-Jan-05, 09:16 AM
So is it scattering of light that make the colors? And the atomosphere determines the colors?

The colours are already there are components of visible light, the molecules in the atmosphere scatters the blue light mostly to create the blue appearance of the sky.

http://home.att.net/~RTRUSCIO/SPECTRUM.htm

George
2007-Jan-05, 05:47 PM
Jupiters colours are explained rather concisely here:
http://antwrp.gsfc.nasa.gov/apod/ap960803.html
Nice. Neptune is interesting because no one, apparently, knows why it is a deeper blue than Uranus. The only explaination so far seems to be due to a chromophore within the atmosphere of Neptune. [I haven't researched it much, however.]

Amber Robot
2007-Jan-05, 06:36 PM
Jupiters colours are explained rather concisely here:

http://antwrp.gsfc.nasa.gov/apod/ap960803.html

From that link:


Some suggest that more colorful hydrogen compounds well up from warmer regions in the atmosphere, tinting the cloud tops. Alternatively, compounds of trace elements like sulfur may color the clouds.

I would agree that it is concise, but it doesn't really say what causes the colors.

George
2007-Jan-05, 08:43 PM
I would agree that it is concise, but it doesn't really say what causes the colors.
Well.......
Color is simply a perception generated within the brain. The parameters which cause the brain to present color as you see it are often quantified in three categories: hue, saturation, and brightness. The signal the brain receives is caused by the reaction of three types of color cones within your eye. These are typically called the red, green, and blue cones. You have about 6 million of these things in each eye.

These cones will respond differently for different colors of light that impacts them. For example, the more blue light that enters the eye, the more active are the blue cones, etc. Thus, the more blue we perceive.

You can think of light as being a wave or a particle, or both. In this case, I like the particle approach. When energetic atoms emit photons, these photons will have a fixed amount of energy depending on how and where they were emitted. The higher energy photons react much more often with the blue cones, and the lower energy photons react much more often with the red cones. Photons which are higher or lower outside of the visible range do not react in a way that allows any color detection. The energy range for these photons is really quite small. The entire range of energy for photons is called the spectrum and the range where the eye can see them is called the visible spectrum.

It is reasoned that evolution has caused eyes of all species to take advantage of this visible range of light because that just happens to be the bulk of the light that comes from the sun.

The sun produces, essentially, photons of every energy level you can imagine within and near the visible spectrum. The intensities (photons per second, or flux) for each energy level of photon varies somewhat in the visible spectrum. [The peak output of the sun is in the blue (not yellow as some would say).] Yet, the sun produces so much intensity of photon flux at all energies within the visible spectrum that it excites our color cones to their maximum reaction rate. This causes us to see white. Since clouds reflect all the photons almost equally, guess what color the clouds are? This is essentially true of the Moon, too.

Sunlight, or other sources of light, will bounce or scatter off surfaces. Some surfaces absorb photons within a certain range of energy levels, yet they will reflect other energy levels. A red apple will absorb the blues and greens and reflect mostly the "red" photons. Thus an apple appears red. Water is more the opposite, it absorbs more of the reds and produces a blue ocean instead.

In summary, there are three important elements to color. The source of light (what colors are being emitted), the objects properties of reflectance, and the response characteristics of our eyes (or eyes/brain, sometimes called the retinex). They all contribute to the wonder of color.

Amber Robot
2007-Jan-05, 09:43 PM
Well.......

That's all fine and good, but ArgoNavis' post had a link that he implies explains why Jupiter's clouds have colors that orange, brown, etc. However, the link actually says that astronomers are hard pressed to explain the colors, as they should be colorless at the cool cloud temperatures, and only offers up two hypotheses. So, perhaps concise, but not definitive.

George
2007-Jan-06, 08:39 PM
Yes, that is obvious. Ironically, I was being rushed to leave and missed that obvious point, yet I did a lengthy, time consuming explanation instead. This isn't far from par for me.:wall:

grant hutchison
2007-Jan-06, 08:44 PM
Ironically, I was being rushed to leave and missed that obvious point, yet I did a lengthy, time consuming explanation instead. This isn't far from par for me.:wall:It's an old problem. Pascal, Twain, St Augustine and others are all credited with a quotation along the lines of: "I apologize for the length of this letter; I did not have time to write a shorter one."

Grant Hutchison

George
2007-Jan-06, 09:29 PM
Thanks for some egg cleanser. :) I had forgotten that quote from Twain, though it is cool to here these other greats used it, too.

It is surprising how many great quotes are quite old. I recently read of Kepler when he stated: "not to throw the baby out with the bath water".

mantiss
2007-Jan-14, 06:10 PM
The sky is blue because the Magratheans have not yet emerged from their deep freeze to offer us custom made luxury planets :p

serpo01
2007-Jan-18, 06:26 PM
Can you please explain what you mean by the "Magratheans" ? Who or what are these ?

cjl
2007-Jan-22, 04:21 AM
It's a reference to "The Hitchhiker's Guide to the Galaxy," in which there was a civilization called the Magratheans who build custom planets to order.

Rickycardo
2007-Aug-25, 08:20 PM
I was reading this page when I came across this explaination for the blue sky:
http://amasci.com/miscon/miscon4.html#blu
What he says seems to make some sense, that air is blue in large amounts like water is blue in large amounts. But I lack the understanding in physics to know if he's a nut case or a genius.
Anyone else who knows more than I (that would be most everyone here) care to enlighten me to this explaination please?
Thanks

hhEb09'1
2007-Aug-26, 12:22 PM
Anyone else who knows more than I (that would be most everyone here) care to enlighten me to this explaination please?
I don't think I know more than you, but it seems like baloney to me:
The sky is blue because air is a powdery blue material, and when the sun shines on it, you can see this blue color. Each molecule of air behaves like a bluish-looking mote of dust. Stare upwards on a sunny day, and you're looking into a thick cloud of air. (There really is no "sky" up there. You're not looking at a blue surface. Instead you're just seeing the Earth's layer of blue air against the blackness of outer space. )He doesn't come right out and say that he disagrees with the idea of scattering--he seems about to assert that each individual molecule would produce the scatter and show a "powdery blue" but he doesn't really go that far.

Manchurian Taikonaut
2007-Aug-27, 12:52 AM
So an animal like an Eagle, which has much sharper vision than a human eye would these creatures see the sky as violet ?

George
2007-Aug-27, 01:13 AM
I don't think I know more than you, but it seems like baloney to me
I agree, and it is misleading. This statement of his alone does little to eschew obfuscation.


The sky is blue because air is a powdery blue material, and when the sun shines on it, you can see this blue color.
The color of objects that we normally see is due to the product of the spectral irradiance incident upon the object and the spectral reflectance properties of the object. A red lazer will reflect brightly off red objects and dimly off non-red objects.

It is different, however, when the particles that light is traveling through are smaller in diameter than the wavelength of light. Brucke first discovered this and Tyndall confirmed it with his great work. Air molecules, aerosols, dust, ash, smoke, some smog and other particles less than the wavelength of visible light cause Rayleigh scattering. This scattering gives great advantage to the blue end of the spectrum as the "blue" light will scatter about 9x more than the "red" light. Thus, we see more blue than any other color.

He is correct about seeing white if more atmospheres are involved since more scattering takes place and the blue light gets scattered away from us. Just how white it would be is likely horribly complex to determine. Mie scattering also enters the picture for light near the horizon.


So an animal like an Eagle, which has much sharper vision than a human eye would these creatures see the sky as violet? Maybe. Many birds have tremendous color vision since they not only have four color cones, to our three, but their cones do not overlap each other in response.

However, the Sun is not all that bright in violet. Also, violet will scatter more often than blue, so it will scatter away through less atmosphere.

Then there is the issue of what the brain decides to do with all the color information, that is unknown, I think, for birds.

Whirlpool
2007-Aug-28, 04:35 AM
Hmm..:think:

So ...why is the ocean color blue too?

Does it because it reflects the color of the sky?

George
2007-Aug-28, 01:04 PM
Hmm..:think:

So ...why is the ocean color blue too?

Does it because it reflects the color of the sky?
Water has the property of absorbing more red light than blue. Air does not absorb much visible light. Reflection of a blue sky will improve the blue appearance, but the main answer for blue water is absorption.

whysky
2007-Sep-11, 06:11 PM
Many people tend to overthink this question. The answer is much simpler and funnier than most people would guess.

http://www.why-is-the-sky-blue.tv/why-is-the-sky-blue.htm

Why is the grass green is another question that calls for a silly answer.

Tilt
2007-Sep-22, 06:18 PM
Tell me why the stars do shine,
Tell me why the ivy twines,
Tell me what makes skies so blue,
And I'll tell you why I love you.

Nuclear fusion causes stars to shine,
Tropisms induce the ivy to twine,
Tyndall-Rayleigh scatter makes the sky look blue,
Testicular hormones are why I love you


(with apologies to Asimov)

Tube
2007-Sep-23, 08:14 PM
As far as education goes, it's counterproductive to give an advanced answer to an introductory level question.

The sky is blue because air is blue.

Solids have color, liquids have color, and gasses have color.

George
2007-Sep-24, 03:57 AM
Is nitrogen or oxygen blue? Air was considered to be blue long ago, but not today.

hhEb09'1
2007-Sep-26, 06:30 AM
The sky is blue because air is blue.I think that is what Rickycardo's link was saying sometimes. That air has an intrinsic color blue. I don't think that that is actually the case.