Shapiro Delay

A general relativistic effect where light takes slightly longer to travel through the local spacetime of a massive object. It was originally detected by bouncing radar signals off Venus and measuring the return time when the Sun was close to the line of sight in between Venus and the Earth. In pulsar timing, we measure the Shapiro delay from the pulses traveling close by the massive, compact companion. It is most easily measured for systems which are nearly edge-on as viewed by us.