Shapiro effect . It is an effect resulting from general relativity according to which the arrival time of a signal that propagates in space is affected by the presence of matter in its vicinity, named after the physicist Irwin Shapiro (not to be confused with the physical Stuart Louis Shapiro ). This effect is the double combination of the fact that the observed signal no longer propagates in a straight line — and therefore travels a longer path than it would be in the absence of mass in its vicinity — and that the passage of time is is affected by the presence of mass.
Is an elementary effect of general relativity, but instead that other effects of this -refracción type of light, precession of the perihelion , shift to red gravitacional- not predicted at the time of the discovery of general relativity, around 1915 , but about fifty years later, by Irwin Shapiro in 1964 . [one]
Temporary- gravitational dilation phase shifts is a delay in the arrival times of the photons passing near the sun . Thus, not only is the light path deflected by the solar gravitational field , but the photons are also slowed down.
This negligible effect was first calculated and observed by Shapiro in 1964 . His experience consisted of measuring the time to and from Earth to Mercury from radio photons emitted on our planet when its path was close to the solar surface. The shorter or longer time to cross this field is related to the relative distances of Earth and Mercury from the Sun.
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- 1 Measurement in the solar system
- 2 Measurement in binary pulsars
- 3 Notes and references
- 4 External links
Measurement in the solar system
The Shapiro effect can be measured in the solar system , especially by studying the arrival times of signals emitted by a probe resting on another planet . The first accurate verification of the measurement of the Shapiro effect was made by Viking probes that landed on Mars .  Previously, the Shapiro effect had been detected by studying the radar echo emitted from Earth and reflected on another planet  This first method was relatively imprecise because the received echo was extremely weak (10 -21 Wfor a 300 kW emitted signal) and because the surface of the planet on which the signal was reflected was relatively large. Conversely, the signals emitted from a probe on a planet were much more accurate, but at a considerably higher cost, since they required sending the spacecraft to a planet. 
Measurement in binary pulsars
It can also detect a binary pulsar where pulsatile extremely regular emission of the pulsar is modulated by the Shapiro effect as a result of the displacement of the pulsar around its companion. In this case, since the effect is directly proportional to the mass of the pulsar’s companion, it allows the mass of the pulsar to be determined under certain conditions. This relativistic effect, which allows determining the mass of one or both of the component stars, knowing the details of the orbit of a binary system , is part of the post-Keplerian parameters. The Shapiro effect in a binary pulsar was first detected in PSR B1913 + 16 , in 1984 , and a few years later on PSR B1534 + 12 in a much more convincing way.