How does the velocity of air molecules affect EM waves?

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Main Question or Discussion Point

I would like to know how exactly or if the velocity of air molecules affect the light i.e electromagnetic waves passing through it. Ignoring the effect of pressure and/or temperature differences in the air which might also affect the light (due to changes in refractive index).
 

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  • #2
.Scott
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If by "air molecules", you mean O2, N2, CO2 and gaseous H2O, not very much.
Assuming we are talking about the Earth's atmosphere:
Unless we are talking about relativistic velocities, absorption will not be change with velocity.
If any of those materials were able to reflect the EM, the EM would never make it through them. So all you have left is the refractive effects.

Although, it would be good to know which EM you are talking about.
 
  • #3
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If by "air molecules", you mean O2, N2, CO2 and gaseous H2O, not very much.
Assuming we are talking about the Earth's atmosphere:
Unless we are talking about relativistic velocities, absorption will not be change with velocity.
If any of those materials were able to reflect the EM, the EM would never make it through them. So all you have left is the refractive effects.
Although, it would be good to know which EM you are talking about.
I actually want to know the effect of wind on twinkling of stars, mostly in the visible spectrum. It's not just about absorption, how about diffraction etc ?
 
  • #4
.Scott
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It's mostly about refractive effects.
Diffraction would require some blocking or reflecting of the star light. O2, N2, CO2, and gaseous H2O (at STP) won't do that.
 
  • #5
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http://coolcosmos.ipac.caltech.edu/ask/210-Why-do-the-stars-twinkle-
The stars twinkle in the night sky because of the effects of our atmosphere. When starlight enters our atmosphere it is affected by winds in the atmosphere and by areas with different temperatures and densities.
Perhaps I should change the title of this thread to "How does the wind contribute to twinkling of stars ?"
 
  • #6
sophiecentaur
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I actually want to know the effect of wind on twinkling of stars, mostly in the visible spectrum. It's not just about absorption, how about diffraction etc ?
That effect is due to refractive index which is affected by density. But I guess you can say that warm air expands and is less dense so there is an implied relationship, in practice, between temperature and particle velocity because of the gas laws. Temperature relates to average molecular speed.
 
  • #7
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It's mostly about refractive effects.
Diffraction would require some blocking or reflecting of the star light. O2, N2, CO2, and gaseous H2O (at STP) won't do that.
What if we consider high frequency EM waves like gamma and X rays will they undergo significant diffraction due to these molecules ?
 
  • #8
.Scott
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What if we consider high frequency EM waves like gamma and X rays will they undergo significant diffraction due to these molecules ?
They get more than just diffracted. The following graphic shows atmospheric absorption across the EM spectrum.
Visible: Yes. Ultraviolet: A little. X-ray: No.
transmissionwindow2.gif
 

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