Does Distant Starlight Become Coherent Upon Reaching Earth?

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Discussion Overview

The discussion revolves around the coherence of light from distant stars, specifically questioning whether light from stars like Canopus becomes coherent by the time it reaches Earth. The conversation explores the implications of coherence in relation to creating astroholograms and the nature of starlight.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions if the light from distant stars becomes coherent upon reaching Earth and whether this coherence could enable the creation of astroholograms.
  • Another participant seeks clarification on the meaning of "coherent," suggesting it may refer to laser-like properties.
  • A participant proposes that the term "polarized" might be more appropriate than "coherent," noting that starlight can be mildly polarized due to scattering and magnetic fields.
  • Some participants discuss the idea that light rays from distant sources may be considered coherent if the angle between them is negligible, although this does not necessarily imply coherence in the strict sense.
  • There is a clarification that parallel light rays being in phase are indeed coherent, but this was not clearly stated in earlier contributions.

Areas of Agreement / Disagreement

Participants express differing views on the coherence of starlight, with no consensus reached on the definitions or implications of coherence in this context. The discussion remains unresolved regarding the nature of starlight and its properties.

Contextual Notes

Participants have not fully defined coherence or clarified the assumptions underlying their statements. The discussion includes varying interpretations of coherence, polarization, and the conditions under which light may be considered coherent.

brianhurren
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by the time light from a distant star reaches us, let's say from Canopus, does the light become coherent?

and if it is coherent, can you make an astrohologram?
 
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How do you mean "coherent"?
http://en.wikipedia.org/wiki/Coherence_(physics )
... like a laser you mean?
Short answer: no.
 
Last edited by a moderator:
Perhaps you meant polarized instead of coherent. That too is essentially untrue. You can test this yourself by viewing stars through a polarized lens, then rotate the lens 90 degrees and see if the stars changes in brightness. Star light can be mildly polarized due to scattering by dust particles over vast distances and also by strong magnetic fields on the star.
 
Last edited:
... possibly just thinking of the light being parallel?
@brianhurren: any of this useful?
 
If two observers are near, the light rays from such a distance source may be considered as coherent because, the angle between the light rays is too small and negligible. Theoretically, this assumption is valid
 
Varadha said:
If two observers are near, the light rays from such a distance source may be considered as coherent because, the angle between the light rays is too small and negligible. Theoretically, this assumption is valid
Saying that light rays are parallel does not mean they are coherent.
 
HallsofIvy said:
Saying that light rays are parallel does not mean they are coherent.

Oh. Sorry. I thought any parallel rays in phase are coherent
 
Varadha said:
Oh. Sorry. I thought any parallel rays in phase are coherent

yes they are, but that wasnt in your statement earlier, you didnt mention anything about them being in phase

Dave
 

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