Does Distant Starlight Become Coherent Upon Reaching Earth?

[brianhurren]

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?

 

[Simon Bridge]

How do you mean "coherent"?
http://en.wikipedia.org/wiki/Coherence_(physics )
... like a laser you mean?
Short answer: no.

 

[Chronos]

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.

 

[Simon Bridge]

... possibly just thinking of the light being parallel?
@brianhurren: any of this useful?

 

[Varadha]

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

 

[Simon Bridge]

Like this?
http://skullsinthestars.com/2008/09/03/optics-basics-coherence/
... OP has yet to logon since that post - but it's early days yet.

 

[HallsofIvy]

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.

 

[Varadha]

Saying that light rays are parallel does not mean they are coherent.

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

 

[davenn]

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