# Deflection of light by the Sun

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?

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.

• 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 3 '14 at 12:23
• @bobie: yes, that's the angular deflection of a ray that just grazes the surface. – John Rennie Aug 3 '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 4 '14 at 4:19
• @bobie: I've updated my answer to respond to your comment – John Rennie Aug 4 '14 at 5:06
• @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 5 '14 at 11:12