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How does the 'atmosphere' of the sun affect ligth from stars passing behind it.

  1. Dec 21, 2008 #1
    When the sun goes down over the horizon, we can still see the sun because the light of the sun is bent by our atmosphere. I would imagine that if one were outside of our atmosphere on the far side of earth away from the sun, yet in a path in line with that light they would also see the sun (even though the sun were technically blocked from their view in a straight geometric line), due to this lensing effect of our atmosphere. Although the sun has no 'atmosphere' exactly, there is still a lot of mass streaming out from it such as hydrogen and helium, and so therefore doesn't it have some optical bending properties? My question here is this: If the sun is to be considered having an 'atmosphere' in any sense that can bend light, how does this affect the results that 'proved' einstein's relativity experiment where light from stars passing behind the sun during an eclipse 'emerged' early from behind the sun? Do the results need to be adjusted for solar atmospheric effects of any such effect if there are any?
     
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  3. Dec 21, 2008 #2
    No, there is certaintly no atmosphere in the sun. I think you misunderstood Einsteins theory of realitivity. What cuases the starlight to bend is the sun's huge mass that bends space-time on which the starlight is traveling through. This cuases the light to bend relative to the sun's mass bending space-time. Read Einsteins general theory of relativity for further information on this specific topic to fully answer your question.
     
  4. Dec 21, 2008 #3
    ugh .. I am fully aware of the gravitational effect of the sun bending light ... but I guess you did not answer my question ... since there IS mass ... a gas such as hydrogen ... WHAT EFFECT IF ANY does it have on bending of light around the sun? CME's ? matter streaming out from coronal holes? Maybe you should check out nasa's site and then come back and tell me that there is no 'atmosphere' ... or at least one that would have absolutely NO effect on light passing the sun ... a transient atmosphere is none the less still an atmosphere ... is it not?

    http://www.spaceweather.com/
     
  5. Dec 21, 2008 #4
    The link you posted says that the density of the "atmosphere" of the sun is 1.3 protons/cm^3

    That is an incredibly thin atmosphere and I would assume any effect is has on light is negligible since it would interact with only a very tiny fraction of any incoming light. I would also assume it doesn't extend very far past the "surface" of the sun, because of the huge gravity the sun produces.
     
  6. Dec 21, 2008 #5

    Janus

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    Another factor to take into account is achromatic aberration. When light is bent by refraction caused by a medium, different frequencies of light refract a different amount. This would cause a rainbow fringe around the image of the star who's light is bent. Gravitational lensing however, bends all frequencies equally. So any bending caused by the light passing through the Sun's atmosphere would be noticeable by its achromatic aberration.
     
  7. Dec 22, 2008 #6
    The 'thinness' of the sun's atmosphere would depend on a lot of factors, such as how much turbulent activity there is on the sun kicking mass off the surface, also the sun has a much larger diameter and although this atmosphere is thin, there is a lot farther to travel through it.

    The 1.3 protons/cm^3 is the density of the solar wind headed to the earth from the sun and NOT the density of our sun's atmosphere. That was just the amount of mass in space headed to the earth in the solar wind (on that particular day).

    As for achromatic abberation, i think this might apply to solid materials as lenses. I watch the sun go down over the ocean and when the bottom of the sun appears to touch the horizon, the top of the sun in reality has already gone behind the horizon; and if i put sunlight through a prism i see the rainbow ... achromatic abberation ... however i don't see this happen at sundown so I guess achromatic abberation does not apply if you are 'in' the lens, and since i have not viewed the sun after it has passed through the atmosphere and back out I really don't know if it experiences achromatic abberation after passing through our atmosphere and then back out into space. Does anyone else know about this? But if this WERE the case, has anyone actually looked at the plates during solar eclipse proving einstein's theory and analyzed them to determine if there were any signs of achromatic abberation present?

    Don't get me wrong here. I do not suggest that the theory of relativity is wrong. I simply want to know if there are other factors in play in the proof that could slightly 'skew' the results. The physics of a star are complex, for example recent observations where mass falls back to the sun ...

    http://www.spaceweather.com/archive.php?month=09&day=29&year=2008&view=view

    Read the article about 'Great Prominence' and there you will find the following statement ... "No one understands why the top of the prominence cascades down as fast as it does; the 'magnetic diffusion coefficient' of the medium shouldn't allow it. At the same time, swirls and vortices indicate an exquisite degree of magnetic control so far impossible to duplicate in Earth laboratories. How does the sun do these things? It's a beautiful mystery."

    The same or other forces at work around or on the sun could possibly account for other phenomena. What I am trying to point out here is that there may be many effects around a star that could to some degree or another affect passing light that are not yet fully understood.
     
    Last edited: Dec 22, 2008
  8. Dec 22, 2008 #7
    Ok ummm guys! Iam completely lost here. The sun has an atmosphere?!
     
  9. Dec 22, 2008 #8

    cristo

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  10. Dec 22, 2008 #9

    Janus

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    The reason you don't notice the achromatic aberration during sundown is due to the fact that the index of refraction for the atmosphere is only 1.00029 (compared to the 1.5 for the glass prism). It's there, its just not pronounced enough to notice with the naked eye.
     
  11. Dec 22, 2008 #10
    So what is the refraction of the sun's 'atmosphere' ?
     
  12. Dec 22, 2008 #11

    Vanadium 50

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    Add another fifteen or twenty zeros to Janus' number.
     
  13. Dec 22, 2008 #12
    Re: How does the 'atmosphere' of the sun affect light from stars passing behind it.

    Found this... " Light refraction by the Sun's atmosphere is calculated. As detected from the Earth, the refraction can deflect a light ray emitted from the Sun's limb by 13'' or a starlight ray grazing the solar limb by 26'' , an effect 15 times larger than the gravitational deflection."

    http://www.springerlink.com/content/etwum62yqqhx8e6d/
     
  14. Dec 22, 2008 #13

    Chronos

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    It think it would also be difficult to talk NASA into pointing the Hubble anywhere near the sun.
     
  15. Dec 23, 2008 #14
    Re: How does the 'atmosphere' of the sun affect light from stars passing behind it.

    Well, I don't know why we need to aim the Hubble at the sun ...

    But now my question is this ... considering the effect of the sun's atmosphere on light of a star passing past the sun and being bent toward earth, shouldn't the results of the proof of gravitational bending of light be adjusted and recalculated? It seems to me that the effect of mass bending space-time may be diminished considerably.
     
  16. Dec 23, 2008 #15

    Janus

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    Re: How does the 'atmosphere' of the sun affect light from stars passing behind it.

    The thing is that even during a total eclipse stars very near the Sun can not be seen because of the brightness of the chromosphere and corona. So to make observations of shifted positions of stars, you have to pick stars far enough from the Sun that their light does not pass through a significant thickness of the Sun's atmosphere to cause refraction.
     
  17. Dec 24, 2008 #16
    Does anyone have a link to the actual experimental data and proofs?
     
  18. Dec 24, 2008 #17

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  19. Dec 25, 2008 #18
    Re: How does the 'atmosphere' of the sun affect light from stars passing behind it.

    The stars WERE measured for deflection after their light passed THROUGH the sun's atmosphere.


    After the eclipse, Eddington himself carefully measured the positions of the stars that appeared near the Sun’s eclipsed image, on the photographic plates exposed at both Sobral and Principe. He then compared them with reference positions taken previously when the Hyades were visible in the night sky. The measurements had to be incredibly accurate, not only because the expected deflections were small. The images of the stars were also quite blurred, because of problems with the telescopes and because they were seen through the light of the Sun’s glowing atmosphere, the solar corona.

    The entire article is here:
    http://www.firstscience.com/home/ar...ein-s-theory-of-relativity-page-3-1_1214.html

    Well, as far as I see it, the sun does have an atmosphere, the effect of the solar atmosphere on light passing through it does bend the rays of light from stars behind the sun as it passes, this effect is 15 times more than gravitational effects and the proof did not take this effect into account, and I do not believe Eddington at that time would have had sufficient knowledge of the sun's atmosphere to know how far away from the sun a star should be so that solar atmospheric phenomena would not influence the results.
     
  20. Dec 25, 2008 #19

    Nereid

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    Clifford Will's The Confrontation between General Relativity and Experiment is, or should be, among the first places you go for things like this.

    And in section 3.4.1, among other "actual experimental data and proofs", we read (emphasis added):
     
  21. Dec 25, 2008 #20
    Good resource, thanks for the link.
     
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