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Shapiro delay

(Shapiro time delay, gravitational time delay)
(EMR delay due to passing near massive object)

The Shapiro delay (or Shapiro time delay or gravitational time delay) is the delay of EMR passing close to a massive object, due to general relativity (GR) effects. The effect was confirmed in the 1960s in an experiment bouncing radar off Venus at a time when such a delay was calculated to be measurable due to the mass of the Sun. This was a GR confirmation, and also demonstrated it must be taken into account regarding precise measurements of EMR transients, such as in pulsar timing array (PTA) studies.

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