The delay experienced by a radio pulse as it passes through curved spacetime around a massive object such as a star; it is also known as the gravitational time delay. In the Solar System, the effect can be detected when bouncing a radar pulse off a planet on the far side of the Sun; in this case the time delay can amount to several hundred microseconds. It arises because the pulse takes a longer path through space on its way to and from the planet than it would have done in the absence of the Sun. A Shapiro delay is also experienced when a pulse emitted by a pulsar in a binary system passes close to its companion star. The effect is an important test of general relativity and is named after the American astronomer Irwin Ira Shapiro (1929– ), who first detected it in 1964.
Subjects: Astronomy and Astrophysics.