Dictionary

The first two tests of general relativity were the comparison between prediction and observation for the perihelion advance of the planet Mercury and for the deflection of light near the Sun. In 1959, measurements of the gravitational redshift provided an additional test. All three effects in questions were predicted by Einstein, and these and subsequent measurements are known as the classical tests of general relativity. Measurements of the Shapiro time delay are sometimes called the “fourth test of general relativity”.

More information about the deflection of light can be found in the spotlight text The gravitational deflection of light, while the connection of this effect with one of the fundamental principles of general relativity is explored in The equivalence principle and the deflection of light.