An Etymological Dictionary of Astronomy and Astrophysics

A → general relativity effect whereby an → electromagnetic signal passing near a massive object takes, due to the curved → space-time,
a slightly longer time to travel to a target than it would if the mass of the object were not present. The Shapiro time delay is one of the four classic solar system tests of general relativity. Radar reflections from → Mercury and → Mars are consistent with general relativity to an accuracy of about 5%. The Shapiro time delay is a significant contributor in → gravitational lens systems.

See also: Irwin I. Shapiro, an American astrophysicist; → time; → delay.