Why Does the Sky Look Blue? Rayleigh Scattering

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    Rayleigh Scattering
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Discussion Overview

The discussion revolves around the phenomenon of Rayleigh scattering and its role in explaining why the sky appears blue during the day and red during sunsets. Participants explore the interactions of light with atmospheric particles, the energy of different wavelengths, and the mechanisms of scattering versus absorption.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that the sky appears blue because blue light has more energy and is scattered more effectively than red light, which is scattered less and thus appears to be filtered out during sunsets.
  • It is suggested that the angle of sunlight entering the atmosphere changes during sunset, contributing to the red appearance of the sky.
  • One participant notes that the perception of the sky's color is also influenced by the sensitivity of human eyes to different wavelengths, particularly blue over violet.
  • There is a clarification that the prism effect is different from scattering, as it involves different refractive indices for different wavelengths rather than scattering phenomena.
  • Participants discuss the distinction between scattering and absorption, emphasizing that scattering does not involve absorption and re-emission but is an instantaneous interaction with a polarizable medium.
  • Questions are raised about the role of momentum in scattering and how photons deviate from their paths when interacting with nitrogen molecules in the atmosphere.

Areas of Agreement / Disagreement

Participants generally agree on the basic principles of Rayleigh scattering and its effects on the color of the sky, but there are nuances in understanding the mechanisms involved, particularly regarding scattering versus absorption and the role of momentum. The discussion remains unresolved on some technical aspects.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the interactions of light with atmospheric particles, the definitions of scattering and absorption, and the specific conditions under which these phenomena occur.

cragar
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is the sky blue because , blue light has more energy so it gets scattered to our eye, and red light has less energy so it gets scattered away from our eye , and when the sun sets the angle the light enters our atmosphere changes , is this similar to white light entering a prism and that might be why sunsets are red . ,
and when the light goes trough the atmosphere are the photons absorbed by the nitrogen and then re-emitted , if not how do the photons interact with the nitrogen and what causes them to be scattered .
 
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cragar said:
is the sky blue because , blue light has more energy so it gets scattered to our eye, and red light has less energy so it gets scattered away from our eye , and when the sun sets the angle the light enters our atmosphere changes

Both red and blue light get scattered in the same directions, it's just that blue light scatters more than red, so we see the sky as being blue. Sunsets look red because the light from the sun has to pass through more atmosphere, and blue light has mostly been filtered out.

EDIT: I should add that the sky looks blue because of shorter wavelengths being scattered more than longer wavelengths AND the fact that our eyes are much more sensitive to blue than say, violet.

cragar said:
is this similar to white light entering a prism

No, the prism effect is because different wavelengths have different refractive indices, has nothing to do with scattering.

cragar said:
and when the light goes trough the atmosphere are the photons absorbed by the nitrogen and then re-emitted , if not how do the photons interact with the nitrogen and what causes them to be scattered .

Scattering is NOT absorption and re-emission. Absorption and re-emission involves transitions between real energy states that possesses a characteristic lifetime, wheras scattering is more-or-less instantaneous. Scattering occurs as a natural consequence of EM waves interacting with a polarizable medium.

Claude.
 
sweet thanks for the answer .
 
No worries!

Claude.
 
Claude , when you say sunsets look red because the blue light has mostly been filtered out ,do you mean by filtered that the blue light was absorbed.
 
Not absorbed, but instead, scattered. Some of the blue light that is "missing" from the sunset you are looking at, is seen as part of the blue sky by someone else in another location.
 
is blue light scattered more because it has more momentum , When the blue photon enters the atmosphere , you said it scatters because it is interacting with a polarizable medium , what cause the photon to deviate from its path , are the electrons in the nitrogen affecting the electric and magnetic component of the photon ?
 

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