deflection of light, relativistic
One of the basic predictions of general relativity is that light is influenced by gravity. For instance, light passing a massive body is slightly deflected. This is the basis for what is called gravitational lensing.
General information about this topic can be found in the spotlight text The gravitational deflection of light, while its connection with one of the fundamental principles of general relativity is examined in The equivalence principle and the deflection of light.