My 7th grade science teacher said that one of the reasons that the sky was blue was because our atmosphere is 80% nitrogen, and nitrogen relects blue while absorbing most of the other colors in the visible wavelengths. (Color photos from space would’ve disproved this hypothesis, but we hadn’t seen any of those yet in 1967.)
He explained red sunsets/sunrises by saying that the angle of the sun’s rays were closer to the ground, and since there was more dust closer to the ground, the light was scattered even more.
I wish I would’ve thought to ask him why Hawaiian sunsets were red even though the Pacific ocean isn’t very dusty.
Where does one go to request a refund for the the taxes paid for education levies?
scr4 has already explained this most of the way, but let me address Jinx:
This is a great question, I don’t know for sure the answer my WAG is that the sun simply doesn’t have much violet light in its spectrum compared to blue due to the shape of the black body curve. Another WAG would be that the mix of light being scattered ‘averages out’ to blue - i.e. your eye is taking the average of scattered rays.
That’s exactly wrong - the sky should appear blue from space too. It is the blue that is scattering, not “the blue scatters towards us and the red scatters away from us”. So, if you look at a chunk of atmosphere from any direction it will appear blue.
No, scr4 is actually giving you layman’s terms for deep physical truths you can learn about in 3rd year college physics, which I assure you is not rote memorization. I remember sitting in that class and saying “Wow! Now I really understand why the sky is blue!” If I remembered any of the math I might be able to help answer the violet question as well.
Let’s try it again. In space, there is no scattering, so you only see light coming from the sun and not from the sky. Therefore, the sky is black. Light is passing through space all around you, but you only see the light coming from the sun.
Let’s simplify the ideas greatly - the sun is shooting light ‘particles’, some red, some blue. The red particles shoot straight through the atmosphere, but the blue particles get bounced around some. It’s like separating wheat from chaff - the blue particles are ‘lighter’ and so get bounced around more, the red particles are heavier and go right through. So, if you look at the sun, red and blue (remember only some blue particles get bounced) particles are streaming straight into your eyeball. If you look at the sky, no red particles are coming towards your eye, but a few blue ones will be, so you see blue (and a lot less light than when you look at the sun.)
When the sun sets, the light passes through much much more air than at noon, so almost all of the blue particles have bounced around and gone away, and only the red particles are able to get straight to your eyeball.
I’ve never been able to decipher Ogre’s posts, so I’ll work with yours. All I know about visual perception is that we have receptors for red, green, and blue light. There may be some uneven distribution, i.e. green receptors are more numerous.
Sounds like a reasonable guess to me, but I don’t know that this is known for sure in these circles.
You are confusion evolution (development of eyesight in general over many many generations of organisms) to the behaviour of one individual organism. It makes sense that we would evolve to see yellow light and not say, gamma rays, but it is a completely different thing to say that our eyes get less sensitive over time to exposure from the sun.
One process is driven by natural selection, the other is reversible (just close your eyes) and probably also useful - it helps you see the non-green animal in the forest of green for example.
Sorry - I didn’t mean to throw in “black body curve” without explaining. A hot object radiates light in a distribution - more in the middle of its frequency, less at either end. A hotter object has a shifted, brighter distribution. So, the sun emits mostly yellow light, and a whole lot less blue and red light than yellow light, for example. A hotter star might emit mostly blue.
The curve is more gentle on the red side, so you get more red than violet out of the sun.
Wait a second, SCR4! I’m confused here! Peak in the green? Then, why is the sun a yellow star? (I’ve heard of Red Giants, but are there Green Giants in space, little sprout? ho-ho-ho!) …Sorry, I couldn’t resist adding that quip!
“They’re coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time… :)” - Napoleon IV
Oh, also, SCR4, I need you to explain:
By that logic, then why don’t we see in UV and IR ranges? …Just being the devil’s advocate, here, to understand your point of view.
“They’re coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time… :)” - Napoleon IV
Sorry, but one more question to confuse everyone! I’m not quite sure how to pose this, but here goes:
OK, if all this blue light is scattered, as explained, with the remaining colors coming straight through the atmosphere…
Then, wouldn’t we expect the blue rays to be superimposed onto the rays of the remaining colors prior to, or perhaps while, becoming incident upon my eye? So, taking this into ocnsideration, I must ask why should one then see the sky as any one distinct color?
My WAG would be to say that the eye is tracing the light rays back to their point of origin, but if the superimposition is occurring as I suggest…wouldn’t it then be impossible for the eye to trace back a distinct blue ray from the muddle of colors in a superimposed mess?
(If I’ve lost you, I’ll see if I can state my question a different way.)
“They’re coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time… :)” - Napoleon IV
Thanks for the link, moriah. It appears that I was wrong on one important detail - the scattering is from molecules, not dust particles.
I don’t think there are clear-cut answers when it comes to the end results of evolution. As for UV though, most natural objects don’t reflect UV very well, and it isn’t terribly useful. A notable exception is flowers - many of them are very bright in UV, and many insects evolved UV vision to find them. Or rather, they evolved together to better help each other.
As for IR, one problem may be that the eye itself is at body temperature and emit some IR. It will be difficult to see through the glowing eyeball. This is less of a problem for cold-blooded animals, and I heard some species of snakes can “see” IR.
Another answer may be that ultra-violet and infra-red are by definition just outside the visible range, and that’s why we can’t see them…
Yellow or white light is a mixture of all colors of light. If you take a lot of green light and a bit less of red and blue light, it becomes a yellow light. It’s a very broad peak, you see.
It might help to look at the diagrams in the link moriah posted. I’ll give it a shot though. Let’s say you are admiring a sunset in Boston. The sun looks orange. Why? Because the blue light has scattered off the path before it gets to Boston. What happened to this scattered light? It’s raining down from the sky onto, say, Chicago. Which is why the sky in Chicago is blue. Of course the Boston sky is blue too. After dumping the blue portion onto Boston, the beam of sunlight continues to Nantuckett where it is admired as a red sunset.
In other words, scattered light hits your eyes from every direction - that’s why it makes up “the sky.” You can only see unscattered light when you look directly at the sun.
The explanation that I’ve heard for the reason that the visible spectrum is at about 400-700nm is that its the most useful range in which water is transparent. A real nice theory, considering that we evolved sight while in the ocean.
(Unfortunately, none of my color theory books say diddly about why the spectrum is where it is, so I can’t back this up.)
Boy, the smorgasbord of evolution theroies has an answer for everything! I bet the creatures who evolved from the sea have the best vision in the hindsight range, too!
“They’re coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time… :)” - Napoleon IV
FYI - the snakes in question are called pit vipers. They include rattlesnakes, water moccasins, and copperheads. They do not see IR with their regular eyes. They have small indentations in their face below their eyes. These indentations, or pits (and thus the name), detect IR. All of this is in a standard encyclopedia.
Those IR pits are an early form of eye. They are patches of skin sensitive to a certain wavelength of EM radiation, with a concave shape that functions to help detect the direction of the source. So the next time you get in a debate about evolution and someone throws out the argument about irreducible complexity and the eyeball, talk about pit vipers and their IR eyeballess sockets.
Yes, evolution and genes are too readily called for to explain everything from black athletes to why the chicken crossed the road.
However, in this case, there is a cogent argument. Water blocks out most of the em bandwidth except for what we know as visible light. Since the underwater is ultraviolet dark, there’d be no advantage for an ultraviolet sense. That’s why evolution can explain that sight covers the visible light range, because the visible light range is somewhat transparent in water, in which we evolved.
Peace.
Daddy, why is the sky blue? I mean, is blue light scattered because its wavelength is the same size as the ubiquitous nitrogen atom or because blue is susceptible to the frequency of the dipolar magnetism of the air molecules?
Actually, you would see in the UV if it were not for the fact that the lens of the eye is opaque at those wavelengths. The blue receptor does respond to UV light, although its peak sensitivity is in the blue.
UV light is one of the causes of cataracts. A cataract is usually fixed by replacing the lens with a plastic one. Usually this plastic one is transparent to UV, so those people can then see those wavelengths.
confused here! Peak in the green? Then, why is the sun a yellow star? (I’ve heard of Red Giants, but are there Green Giants in space, little sprout? ho-ho-ho!) …Sorry, I couldn’t resist adding that quip! 