Deflection angle of a ray grazing the sun

[spidey]

I saw in a website that Einstein found the deflection angle of a ray grazing the sun through this relation
alpha=4GM/c2r=1.74 arc sec
but when i used this relation by giving values i didnt get this value 1.74...wats wrong..can anyone solve this ...

 

[spidey]

I got the answer 1.74...i multipled the answer by 206264 to convert it into arcsecs..
can anyone tell me how to derive this alpha...alpha=4GM/c2r

 

[shalayka]

'A First Course in General Relativity' by Bernard Schutz explains a lot of the solar system tests.

These might help:
http://www.mathpages.com/rr/s6-03/6-03.htm
http://www.theory.caltech.edu/people/patricia/obsertop.html
http://www.lacosmo.com/DeflectionOfLight/index.html