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Can you give details of a recent experiment of deflection of light by the Sun?

What is the distance from the surface of the Sun and what is the exact value of the angle of deflection?

Qmechanic
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bobie
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1 Answers1

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Have a look at the Wikipedia article on Tests of General Relativity. The most recent measurement quoted there was by a group from the University of Texas. You can find a copy of the paper here.

They measured a deflection of $1.66$ arcseconds $\pm 10\%$, compared to the prediction from General Relativity of $1.75$ arcseconds.

Respond to comment:

The angular deflection of the light at a distance $r$ from an object of mass $M$ is approximately given by:

$$ \theta = \frac{4GM}{c^2r} $$

Put in the mass and radius of the Sun and you'll find $\theta = 8.48 \times 10^{-6}$ radians. Convert this to degrees and multiply by $3,600$ to convert to arcseconds and you'll recover the figure of $1.75$ arcseconds I quoted above.

John Rennie
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  • Is there specified the distance from the Sun? I couldn't find it. Should I assume it was just grazing the surface , at 7c from the centre? – bobie Aug 03 '14 at 12:23
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    @bobie: yes, that's the angular deflection of a ray that just grazes the surface. – John Rennie Aug 03 '14 at 14:10
  • Aren't there any data relative to rays passing at a certain distance from the Sun? Do we know how the angle of deflection varies with distance? – bobie Aug 04 '14 at 04:19
  • @bobie: I've updated my answer to respond to your comment – John Rennie Aug 04 '14 at 05:06
  • That formula is theory, I was looking for different experiments at different distance. Probably when distance is greater tan R the angle of deflection is too small to be measured?...btw,.... isn't 4GM/c^2r the angle or rather tangent 'theta'? – bobie Aug 05 '14 at 04:29
  • @bobie: I don't don't know of experiments to measure $\theta$ as a function of distance. The 10% error in the paper I cited suggests you could make the measurements for $2r_{sun}$ or with some effort $3r_{sun}$. Beyond that would be hard. – John Rennie Aug 05 '14 at 11:11
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    @bobie: the equation I gave is an approximate equation that works when $\theta$ is small. At these small angles the difference between $\theta$ and $\tan\theta$ is negligable. – John Rennie Aug 05 '14 at 11:12