We are currently studying general relativity in school and also had a brief look at gravitational lensing. My teacher gave us the angle of deflection between the apparent location of a star and its actual location (as seen on picture) to be
theta = 1.75" R/d where R is the radius of the object and d is the distance at which the light beam passes the massive object.
Our teacher was not very clear on where this is applicable and showed no derivation.
The equation does not contain mass or density as a variable which irritates me. Does this mean that the formula only works for a specific stellar object (e.g. Is it tailored to the sun's lensing or does it work for a different object as well?)
Could it also be that R and d are different variables than what I have mentioned?