I was reading a book where Precession of Mercury's perihelion was described using general relativity. There I found the following equation:
$$ F \approx \frac{G M_m M_s}{r^2}\left(1+\frac{\alpha}{r^2}\right) $$ Where $\alpha$, he states to be expressed by speed of light, mass of sun, eccentricity of the orbit. This equation seems to be an extension of Newton's Gravitational Law but the author didn't specify how the equation came. Can anyone provide with the derivation of this equation or any reference?
