Is the Spectrum Always Consistent with the Source?

[kumar5]

Hello,

In our day to day life, we see objects from distance in same shape and colour. Sunlight also reaches to us in somewhat same spectrum as it is emitted from sun.

As such, why spectrum, interfered by atmosphere, is not changed or distorted--normally?

Whether emitted, reflected or transmitted spectrum allways persist--somewhat alike sprit of a substance?

Best wishes.

 

[Danger]

It's changed all of the time, kumar. Every time that there's a change in the refractive index that the light is going through, the spectrum is somewhat altered. That, after all, is why the sky is blue.
It is also (immeasurably, perhaps), shifted according to whether you are moving toward or away from the sun.

 

[kumar5]

Still, how it remains grossly the same?

 

[Astronuc]

Sunlight also reaches to us in somewhat same spectrum as it is emitted from sun.

As such, why spectrum, interfered by atmosphere, is not changed or distorted--normally?

As Danger indicated, the spectrum is changing all the time - particularly with different amounts of dust and clouds in the air. The orientation of anyone place on the Earth with respect to incident light from the sun changes constantly due to rotation of the earth, and this in turn changes the depth of atmosphere through which sunlight is transmitted. That's why the sun appears redder at sunset - blue light scatters more than red light.

 

[kumar5]

Still there is some persitency in spectrum lines of sunlight.

Anyway, why we could see and recognize some object at distant place?

 

[Danger]

I see... you mean the gross frequency content of the light. That's because the sun is a constant source. The same elements are providing the photons all of the time (primarily hydrogen and helium). Every element has its own characteristic emission/absorption lines, which don't vary over time. Astronomy would be in a sad state if that weren't true, because it's how we determine the composition of other stars, dust clouds, etc.. Spectrographic analysis of material here on Earth would also be impossible otherwise.

 

[kumar5]

Yes, but atmosphere will also be a constant source for interfearances.

Moreover we can see any object similarily. How it can happen?

 

[DaveC426913]

Light rays are very, very straight and very, very fast. It takes a lot of messing with them to distort them.

The atmosphere bends light only a small bit. It is only noticeable over many miles of distance.

Let me ask you something: have you looked at buidlings, trees or landscape from, say twenty miles distance?
Are the colours the same intensity, or are they very faded?
Are they still across the spectrum, or are distant objects mostly bluish?
Is everything perfectly sharp, or is it fuzzy, indistinct and even a little wavy?
If you look across tha large body of water, are objects at the horizon perfectly shaped are are they grossly distorted?

 

[chroot]

I'd just like to point out that, while the atmosphere is mostly transparent to visible light, it is far from transparent to other wavelengths. Infrared, ultraviolet, X-rays, and other forms of electromagnetic radiation are all scattered or completely absorbed by our atmosphere.

In fact, you could even make the argument that we evolved to use visible light for our sense of vision because it happened to be the band of wavelengths that "survive" the best in our atmosphere without much scattering or absorption.

- Warren

 

[kumar5]

Light rays are very, very straight and very, very fast. It takes a lot of messing with them to distort them.

The atmosphere bends light only a small bit. It is only noticeable over many miles of distance.

Then say in common, these are not effected grossly by interfering atmosphere and my pesist??

Let me ask you something: have you looked at buidlings, trees or landscape from, say twenty miles distance?
Are the colours the same intensity, or are they very faded?
Are they still across the spectrum, or are distant objects mostly bluish?
Is everything perfectly sharp, or is it fuzzy, indistinct and even a little wavy?
If you look across tha large body of water, are objects at the horizon perfectly shaped are are they grossly distorted?

Yes but that may be due to capacity of our eves We still can see clearly by help of lenses.

 

[kumar5]

chroot,In suh view. can we cnsider visible/reflected spectum can persist for long--may be wondering?

 

[DaveC426913]

Light rays are very, very straight and very, very fast. It takes a lot of messing with them to distort them.

The atmosphere bends light only a small bit. It is only noticeable over many miles of distance.

Then say in common, these are not effected grossly by interfering atmosphere and my pesist??

I didn't quite catch that. Say again?

Let me ask you something: have you looked at buidlings, trees or landscape from, say twenty miles distance?
Are the colours the same intensity, or are they very faded?
Are they still across the spectrum, or are distant objects mostly bluish?
Is everything perfectly sharp, or is it fuzzy, indistinct and even a little wavy?
If you look across tha large body of water, are objects at the horizon perfectly shaped are are they grossly distorted?

Yes but that may be due to capacity of our eves We still can see clearly by help of lenses.

Nope. Try it. Look at the something very far away (10+ miles) through binoculars. It will be faded in colours, hazy blue-grey, very indistinct and possibly even wavy.

 

[3trQN]

I was watching a Bumble-Bee yesterday, while trying to get my head round calculus, in my conservatory. It was constantly trying to fly through the plexi-glass roof even though to me it was blatently not completley transparent. I thought to myself how it was odd that it didnt wise up and fly out the door it came in through, since they have the abillity to navigate so well why would they have trouble with the plastic?

Well i came to the conclusion that it was most likley due to their inabillity to distinguish between the frequencies of light that pentrate the plastic. Therfor although the plastic is slightly opaque to me, to the bee it was transparent and no different from the sky.

After all, i read somewhere that the bees eyes are more atuned to UV light and that the flowers have vivid colors in this light spectral range.

I also chuckled and thought that i am blind to so many frequencies of EM and how strange it would be if i could see them all all the time. Then i wonder if there is a circumstance where i am like the bee, banging on some plexi-glass somewhere.

Anyway, Just thought id share that as it seemed fitting.

 

[Danger]

Good theory, 3. It would explain why my windows always end up full of bugs. I never thought of that possibility. I wonder if tinted windows would have the same effect.

 

[kumar5]

I didn't quite catch that. Say again?

Originally Posted by DaveC426913
Light rays are very, very straight and very, very fast. It takes a lot of messing with them to distort them.

The atmosphere bends light only a small bit. It is only noticeable over many miles of distance.

This tells that atmosphere may effect lights a small bit.

Nope. Try it. Look at the something very far away (10+ miles) through binoculars. It will be faded in colours, hazy blue-grey, very indistinct and possibly even wavy.

It may be slghtyly dim but still spetra is maintained.

 

[Gokul43201]

Still, how it remains grossly the same?

It remains "grossly" the same because the medium of propagation of light is a low density gas. If our atmosphere were made of water, you'd really not be able to see things very well.

PS : Please keep your questions clear and specific.

 

[Claude Bile]

The OP may be enquiring as to why the spectral (absorption) lines, from say, the sun, don't shift in frequency as they pass through, say, our atmosphere.

If so, then the answer is due to the linear response of the atoms and molecules to an applied EM field. To get the generation of new frequencies you need a nonlinear response.

Does that answer your question kumar?

Claude.

 

[kumar5]

But all constituents of environment are nor similar and persisting?

Will it also happen similarily with emitted or reflected spectrums from Earth to space?

Gokul, sorry my first language was not english. However I shall try. Meantime pls accomadate.

 

[Astronuc]

Adding to what Danger mentioned, the sun is like a black body radiator with an approximate temperature of about 5800 K, and therefore the sun's light (and spectrum) are fairly constant. The Earth's atmosphere is fairly constant, except for clouds and perhaps dust blown into the air.

See these articles about the sun -
http://en.wikipedia.org/wiki/Sun
http://en.wikipedia.org/wiki/Structure_of_the_Sun#Photosphere

And about the visible spectrum -
http://en.wikipedia.org/wiki/Optical_spectrum

and particularly
http://en.wikipedia.org/wiki/Image:Atmospheric_electromagnetic_transmittance_or_opacity.jpg

The Earth's atmosphere 'scatters' light and during the course of a day, the atmospheric conditions will change, and the scattered light will have the same spectrum, but with different intensities of particular frequencies (wavelengths). It is the intensity of the lines that changes.

Adding to what Gokul mentioned, if one goes underwater, one sees a dramatic changed in the spectrum as one goes deeper. The blue and red light frequencies are absorbed quite readily and IIRC, the yellow frequencies are the most visible many meters underwater.

 

[DaveC426913]

It was constantly trying to fly through the plexi-glass roof even though to me it was blatently not completley transparent. I thought to myself how it was odd that it didnt wise up and fly out the door it came in through,

Because, literally, bees cannot "wise up".

While it seems like they have some very sophisticated mechanisms for locating food and home, like all insects, their complex mechanisms are really composed of layers of very simple mechanisms.

When in reduced light conditions, insects fly towards light. Period. They cannot stop this mechanism. If they manage to find their way into a place where the brightest light comes from one particular direction, they will fly toward it till doomsday. This is not a thinking process, it is more basic than that.

I saw on a nature channel once, the explanation about why moths flutter around night lights. The amount of light that impacts their wings affects the flapping mechanism of the wings. If there is more light on the left wing than on the right wing, this causes the right wing to "speed up" and the left wing to "slow down" (ultra-simplification), resulting in a turn towards the light. There is no brain processing and no decision-making going on here at all.

The roomba robot vacuum cleaner uses this level of logic. It doesn't think, it just has very simple mechanisms that will get it out of most jams.
"If your forward sensors contact something, back up, turn a little, resume."
95% of the time this kind of logic works great. 5% of the time it doesn't.

Bees did not evolve in a world containing enclosed spaces with transparent rooves.

The insects do have what may be one extra parameter to this mechanism: "add a random element to the length of turn or distance".
With this extra element, the bumble bee may, after the 100th try, accidentally stumble upon the nearby-yet-lesser-lit open door - and escape.

 

[3trQN]

Thanks for that, that did also cross my mind, and it seemed like the more simplistic model ( principle of parsinomy i should know better ), however it seemed that the clear glass of the side windows and the open door would be brighter ( less opaque ) than the plexi-glass roof.

Of course you are correct, from the point of view of the bee ( which was up in the rafters ) its possible that up was just the only option. I didnt realize how automated they were.

 

[kumar5]

The Earth's atmosphere 'scatters' light and during the course of a day, the atmospheric conditions will change, and the scattered light will have the same spectrum, but with different intensities of particular frequencies (wavelengths). It is the intensity of the lines that changes.

Thanks. It tells me that wavelengts don't changes in atmospheric conditions but their intensities only changes.

What happens to emitted or reflected spectrums from earth?

 

[Astronuc]

What happens to emitted or reflected spectrums from earth?

That probably depends on the frequencies. For example, infrared emission changes with temperature and composition. As the temperature and humidity of soil (earth) changes, so would the emission spectrum. Similar emission/reflection from green leaves will be different from red, orange, yellow or brown leaves. Deciduous leaves change with the seasons.

Also, snow reflects light which would be otherwise be absorbed by the ground, and that energy would be emitted in infrared wavelengths. The snow cover changes with the seasons at the northerly and southerly latitudes, and on many mountains.

 

[Danger]

It makes a difference, as well, if he means small e 'earth' as in 'dirt', or capital E 'Earth' as in the 'the planet'. The latter, of course, is primarily water and ice caps, which (as you pointed out) have a totally different albedo than the land portions.

 

[DaveC426913]

That probably depends on the frequencies. For example, infrared emission changes with temperature and composition. As the temperature and humidity of soil (earth) changes, so would the emission spectrum. Similar emission/reflection from green leaves will be different from red, orange, yellow or brown leaves. Deciduous leaves change with the seasons.

Also, snow reflects light which would be otherwise be absorbed by the ground, and that energy would be emitted in infrared wavelengths. The snow cover changes with the seasons at the northerly and southerly latitudes, and on many mountains.

Note that Astronuc's examples are *not* changes in the frequency of the light "in transit" (like Doppler shift is**), but are "light absorption by matter and then emission at a different frequency", which I don't think is what the OP was talking about.

**Actually, even Doppler shift is only an apparent shift in frequency.

I can think of only a single circumstance offhand where light changes frequency by itself: intergalactic redshifting.

 

[Danger]

I beg to differ, Dave. Granted, you are the real scientist, not me. Still, I get the distinct impression from the OP's posts (however incoherent some of them seem) that he is referring to refraction, which is totally about absorption and re-emission of photons. He has repeatedly mentioned the atmosphere, so deep-space transit is not at issue.

 

[DaveC426913]

I beg to differ, Dave. Granted, you are the real scientist, not me. Still, I get the distinct impression from the OP's posts (however incoherent some of them seem) that he is referring to refraction, which is totally about absorption and re-emission of photons. He has repeatedly mentioned the atmosphere, so deep-space transit is not at issue.

Well, technically I suppose. But I see a pretty big difference between light passing through the atmo and light hitting snow and being re-emitted as IR.


P.S. I'm perceived as a scientist? Cool. I would have you continue to believe this.

 

[Danger]

P.S. I'm perceived as a scientist? Cool. I would have you continue to believe this.

Well... ****, duh... you have that 'Science Advisor' badge, which I'm pretty sure didn't come out of a cerial box. (And even if it did, I admire your expertise.)