Gravitational red shift

A red shift in the light spectrum of a tiny star was detected, supporting Einstein's theory of general relativity. This observation showed that light loses energy and reddens when rising in a strong gravitational field.
 Walter Sydney Adams United States 1925 Gravitational red shift

A red shift in the light spectrum of a tiny star was detected, supporting Einstein's theory of general relativity. This observation showed that light loses energy and reddens when rising in a strong gravitational field.