Shapiro time delay

What you are seeing: a light signal traveling from an emitter to a receiver passes near a massive body (the Sun at the origin). In flat space the signal would travel in a straight line parallel to the $x$-axis at impact parameter $b$. In General Relativity the signal experiences a time delay $\delta t = 2M \ln(4 r_E r_R / b^2)$ relative to the flat-space expectation, where $r_E$ and $r_R$ are the emitter and receiver distances from the Sun.

The delay is logarithmic in $b$, growing rapidly as the signal grazes the body. For light grazing the Sun, the round-trip Cassini delay was about $250$ microseconds; Bertotti, Iess and Tortora measured it to high precision in 2003 to test the PPN parameter gamma.