Red or Blue Shift: Moving Light Sources Forward/Backward

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Discussion Overview

The discussion centers on the application of red and blue shifts in the context of moving light sources and observers. Participants explore the conditions under which these shifts occur, particularly focusing on relative motion between the observer and the light source.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that red and blue shifts depend on the relative velocity between the source of light and the observer.
  • It is proposed that moving towards a light source results in a blue shift, while moving away results in a red shift.
  • One participant questions whether the shifts apply when moving the light source itself, suggesting that if there is no relative velocity, there would be no Doppler shift.
  • Another participant confirms that the Doppler shifts are relevant when moving towards or away from a light beam but not when moving the light source with them.
  • Specific examples are provided, such as the Andromeda Galaxy being blueshifted and the Sombrero Galaxy being redshifted, indicating real-world applications of these concepts.

Areas of Agreement / Disagreement

Participants generally agree that red and blue shifts are determined by relative motion, but there is some uncertainty regarding the implications of moving the light source itself. The discussion remains unresolved on the nuances of how these shifts apply in different scenarios.

Contextual Notes

Limitations include the dependence on definitions of relative velocity and the specific conditions under which Doppler shifts are observed. Some assumptions about the observer's frame of reference may also be implicit.

lnsanity
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I want to know if the red or blue shift apply if I am moving away or toward a light beam and if it still apply if I am moving the light beam source with me forward or backward.
 
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That is the entire reason for red/blue shifts of electromagnetic waves. When one is stationary with respect to the galaxy or source of light in question, and that light is moving radially toward us or away the waves will be stretched or contracted depending on it's motion. This doesn't mean that perceptually you will see "red" light or "blue" light, but when analyzing the spectrum you can determine where the lines ought to be and where they actually are, shifted towards the blue or red end of the spectrum. The same stands for the light in your hand although you wouldn't be able to tell the difference due to the slow velocity with which you're moving the light source.
 
lnsanity said:
I want to know if the red or blue shift apply if I am moving away or toward a light beam and if it still apply if I am moving the light beam source with me forward or backward.
The Doppler shifts depend only on the relative velocity between source and observer.
 
clem said:
The Doppler shifts depend only on the relative velocity between source and observer.

So that mean it apply when I am moving away or toward a light beam but does not apply when I am moving the light beam source with me forward or backward right ?
 
yes you´re right.
if the light source is moving towards you(or if you´re moving towards the light source if you will), the electromagnetic waves(visible light for instance) will be shifted towards blue.
if the light source is moving away from you, the electromagnetic waves will be shifted towards red.
 
lnsanity said:
So that mean it apply when I am moving away or toward a light beam but does not apply when I am moving the light beam source with me forward or backward right ?
If there is no relative velocity, there is no Doppler shift.
 
Andromeda Galaxy= moving towards us=blueshift
Sombrero Galaxy=moving away from us=redshift
 

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