wbeaty wrote:Nope. You've got the very misconception that this comic is designed to fight.
Not really. There are, however, numerous misconceptions in your response. I'll try to address them one by one.
wbeaty wrote:Ask yourself what material up there is colored blue?
Just because we see a color somewhere, doesn't mean that there is any material colored that way. Our eyes perceive light, not material.
If I blow fog into a room with a fog machine and shine red light on it, the room will appear to be filled with a red haze. The answer to the question "what material is in the room that is colored red" is of course "none". The fog itself certainly isn't red; it's colorless white. To say that the fog "is red", just because we happened to shine red light on it, would completely devoid that statement of any significance - such as a distinction from a genuinely red fog (i.e. one that would appear red under a white light).
wbeaty wrote:Sunlight shines on air, reflected blue light hits our eyes: air is a blue material.
First of all, what hits our eyes when we look at the sky isn't reflected light - it's scattered light.
Second, and more importantly: when light - even white - shines on air, it's not automatically the case that blue light hits our eyes. Often, red, yellow, or other-colored light hits our eyes. In the most generic case of diffuse white lighting - one that we generally use as a standard for evaluating color - we would simply see white light. There is no basis for calling the air blue - any more than calling it red, yellow or white.
wbeaty wrote:Air is a colored material, but it's not a pigmented material.
Air is indeed not a pigmented material, but it is also not a colored material. Not any more than you can say a CD is made of colored material, just because you can see colors on it when you light it in a particular way. Under diffuse white light, air doesn't have any color (and neither does a CD, discounting the sometimes fancifully dyed plastic).
wbeaty wrote:Believing that air is colorless, where the blue color must have some other origin, that's the same basic mistake as believing that bluejay feathers are colorless, or that Morpho butterflies are colorless, or aerogel or opals are colorless.
All of those other examples you cited do appear colored under a diffuse white light. But not air. Air is not blue under a diffuse white light. It's colorless.
wbeaty wrote:Correct question/response would be: Q: Teacher, why is the sky blue? A: because the air itself is blue (but a very dilute blue, a miles-thick layer is needed in order to see the color.)
No. Even if you take a miles-thick layer of air, it still won't appear blue. Not unless you light in a particular way to make it glow blue. (Or red.)
You can verify this next time you are under a completely overcast sky (which gives out diffuse white light). The air won't appear blue, no matter how far away you look. Distant mountains won't be blue-hued; they will simply fade into a gray mist. You will see the true color of air: none.
wbeaty wrote:A: because of Rayleigh Scattering (also called Tyndall effect,) and the color of the air can change depending on the angle of light shining on it. If light shines on air from the side, it's blue. If light shines on air from behind, it's orange or red.
This should have rung a bell - clearly, if the air appears red
when we shine light on it in a particular way, there is no basis for calling it blue, as opposed to red. What reason is there for calling it blue, and not red? Because we like shining from the side more than we like shining from behind?
If I shine light on my CD in one angle, it will appear to glow blue. If in another angle, it will appear to glow red. With another angle, green. Therefore, my CD is green? No.
wbeaty wrote:it's the air-layer which is blue.
Except that it isn't blue. Not unless it's lighted in a particular way. If it's not lighted in a particular way, it's not blue.
wbeaty wrote:The real trouble is that a mile-thick layer of air is far too thin to detect the color. Try a thicker 20mi layer instead.
Yes. You try that, next time your sky is completely overcast with a thick layer of clouds. Look at some landmark 20 miles away (visibility is often surprisingly good under an overcast sky), and report back to us with what color you saw. Was it blue? Was it red? Any color at all?
wbeaty wrote:Sometimes the blue of the air above us is actually the blue light that's been removed from the "sunset rays,"
Finally I can agree with something - the blue of the sky above is actually the blue light taken from sunshine (but only when the atmosphere is lighted in a particular way). It's not the color of the air in any meaningful sense.
(Just like the colors we can sometimes see on a CD are taken from the source of illumination - but neither of them is the color of the metal layer.)
wbeaty wrote:air is behaving like the special ink seen on USA dollar bills: the ink has a color, but tilt the money, or move your head, and it has a different color.
I agree with this, too. So which color is this special ink - is it green, or is it golden red? It should be apparent that you can't say either. And yet, you've made that fallacy with air - you assigned it the color blue, even though it can just as well appear red. What basis is there for picking blue over red? None.
If we want to find out a color of a material regardless of lighting conditions, we can view it under diffuse white light. Under diffuse white light (shining uniformly from all sides), the ink on a bill (not a US bill, but another similar bill I have at my disposal) appears dirty brown (regardless of angle). Air, under diffuse white light, appears colorless. - This is the best we can come as to the inherent color of the material.