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Why are the atmosphere's main elements ( Nitrogen and Oxygen) transparent to visible light.
And what makes most gases have low absorption?
And what makes most gases have low absorption?
kenewbie said:<snip>
This is one of the reasons why your car gets so damn hot in the summer: Light comes though the windows and bounces from the interior. It looses some energy during that bounce, and becomes a heatwave. Same thing, different frequency. Only, heat does not pass unaltered through the glass, so it is trapped inside and bounces back and forth, heating your car.
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Andy Resnick said:This is not true- simply allowing the IR radiation to get into the car and be absorbed by the car interior is sufficient to explain the behavior. One not need presume that visible light be 'down-shifted' to IR radiation, nor that IR radiation be 'captured' within the car interior. Neither occurs.
Finally, a small quibble- heat and IR radiation are not the same things.
I though the idea here was that windows are transparent to visible light but somewhat opaque to IR.Andy Resnick said:This is not true- simply allowing the IR radiation to get into the car and be absorbed by the car interior is sufficient to explain the behavior.
DaveC426913 said:I though the idea here was that windows are transparent to visible light but somewhat opaque to IR.
Schirillo said:The question is really straight-forward. Light waves reflect off of objects that then stream into the eye by first traveling from the object through open space. How is it that we determine where the object is located? That is, why don't we "see" the stream of light waves as they travel in the open space (so that it appears like a colored volume rather than a distant opaque surface)? Instead we somehow decide that the stream of light originates at the surface of the object and then we eliminate our perception of that stream from the intervening space.
Schirillo said:But the question remains, how does the eye (or a machine) "know" that the light originates at the opaque surface (and not closer to the eye)? Machines don't have depth perception. They only "see" in two-dimensions, without imposing some amount of empty (transparent) space between their receptors and the surface.
Schirillo said:The question is not what actually exists (I know the light originates at the surface), it's what is perceived; just like the perception of transparency.
It does have to do with knowledge, since machines cannot perceive depth unless they emit a signal that bounces back off the surface (like bats using echolocation). There is no way to determine depth from just an incoming signal.
Schirillo said:It's not "silly". You can see objects in depth with just one eye (cover one eye and notice that virtually nothing changes), however machines need stereo (or some form of triangulation). The incoming signal DOES NOT include depth information, it only contains wavelengths of light, not an additional signal as to where those wavelengths originated.
sylas said:Pretty much everything you've said above is flatly wrong.
The idea that the incoming signal does not contain depth information is false. How do you think the eye figures it out? It figures it out because light signals have direction, which gives a different view in two eyes. This is depth information. You look at the angle from which a signal comes, in one eye and in the other (triangulation).
As I said before, there is quite a lot of work with robots that do depth perception using binocular vision, just like we do. They don't use magic; they just use the incoming signal.
You also get a much less effective depth vision with one eye, by changes in focus; which is pretty much the same thing but over the space of the retina rather than the space between two eyes. It is, of course, nonsense to say that covering an eye changes virtually nothing. It kills your depth perception, and that makes a huge difference, as anyone who has an eye out of action for any time swiftly discovers. You need stereo vision to get at the depth information available in light coming from some object.
Getting back to the point of the thread. The transparency of air is a physical aspect of light signals passing through air. The transparency of air is a property of light and air, not of the eye and mind.
Schirillo said:It's not "silly". You can see objects in depth with just one eye (cover one eye and notice that virtually nothing changes)
Schirillo said:None of these answers make sense. If we see though air (i.e., it appears transparent) because it's molecules are less dense than light waves of the visible spectrum, how do we "know" that the light comes from the surfaces of objects. That is, how do we attribute the light to the surface and not the air in front of the surface?
Schirillo said:It's not "silly". You can see objects in depth with just one eye (cover one eye and notice that virtually nothing changes), however machines need stereo (or some form of triangulation). The incoming signal DOES NOT include depth information, it only contains wavelengths of light, not an additional signal as to where those wavelengths originated.
DaveC426913 said:Schirillo has a point that can't be denied, though I'm not sure he's on the right track. There is is property of reflected light that hints at an object's distance: Focal length.
sylas said:That's an odd remark, since you have just denied the point he was making in what you quoted. You quoted the extract where he says "The incoming signal DOES NOT include depth information", and then go on to explain, correctly as others have done also, why his point is wrong.
Cheers -- sylas
DaveC426913 said:Well, I'm not sure if I'm saying he's wrong or right about this particular comment; I'm just backing him up in his original assertion that the light rays (at least, collectively) do contain information about depth.
The depth information is conferable from the angle of divergence of the light rays which, through the diamter of the pupil, the action of the lens and finally the image on the retina, is decodable.
DeShark said:I thought that air was quite transparent to almost all wavelengths. I think the reason (as already stated) is that the absorption band is discrete and not continuous and therefore the light passes through. As to why there is a discrete energy spectrum in small molecules (such as water, air, gas, etc) is to do with the separation of the discrete energy levels of individual atoms (a phenomena which arises from the solution of a central potential). In bringing together atoms (so that their potentials overlap), the band is split. With an infinite number (or just very very large) the band is split so much that it forms a continuum. So in solids, the spectrum becomes continuous and so it can absorb many different wavelengths and appears opaque. However, in gases and liquids, there are only a few atoms bound together so a discrete spectrum forms and most light passes through unhindered.
The evolution of our eyes to make the air transparent is not relevant as far as I can see. We use glass because it's transparent, not the other way round. Unless someone can prove me wrong?
The air is transparent because it is made up of mostly nitrogen and oxygen molecules, which are small and do not absorb visible light. This allows light to pass through the air without being scattered or absorbed, making it appear transparent to our eyes.
Most gases have low absorption because they are made up of small molecules that do not interact strongly with light. This means that they do not absorb or scatter light as it passes through, allowing it to travel through the gas without being significantly affected.
Yes, the composition of the air can affect its transparency. For example, if the air is polluted with particles or gases that do absorb or scatter light, it can appear less transparent. However, the main components of air (nitrogen and oxygen) will still contribute to its overall transparency.
No, the transparency of air can vary at different altitudes. As you go higher in the atmosphere, the air becomes thinner and contains fewer particles and gases that can absorb or scatter light. This means that the air at higher altitudes may appear more transparent than at lower altitudes.
The transparency of air plays a crucial role in our daily lives. It allows us to see clearly, as light can pass through the air without being distorted. It also allows plants to photosynthesize and produce oxygen, which is essential for our survival. Additionally, the transparency of air helps regulate the Earth's temperature by allowing sunlight to reach the surface and warm it, while also allowing heat to escape back into space.