Caption: "The gravitational redshift of a light wave as it moves upwards against a gravitational field (caused by the yellow star below)." If you consider the light wave as moving downward, it has a negative gravitational redshift which is, of course, a gravitational blueshift.

Features:

1. Light beaming opposite/aligned to the direction of a gravitational field (which often beaming outward/inward from a gravitational well: i.e., a source of gravity) is redshifted/blueshifted and loses/gains energy.

2. The effect is called the gravitational redshift. As indicated in the preamble, a negative gravitational redshift is a gravitational blueshift.

3. The gravitational redshift is a related effect to the Doppler effect and the cosmological redshift. Some might call it a sort of Doppler effect, but NOT yours truly.

4. The gravitational redshift is an elementary prediction of general relativity made by Albert Einstein (1879--1955) in 1907 which was 8 before the full theory of general relativity was presented (see Wikipedia: Gravitational redshift).

5. The first valid astronomical verification of the gravitational redshift was in 1954 (see Wikipedia: Gravitational redshift: Astronomical observations).

6. The first terrestrial verifaction was in 1959 using gamma rays going downward by 22.5 m in a vertical shaft in a tower located at Harvard University. The Moessbauer effect (discovered 1958) was needed to obtain sufficient accuracy/precision. For the history, see Wikipedia: Pound-Rebka experiment. Point of interest, the lead experimenter Robert Pound (1919--2010) was born in Ridgeway, Ontario, Canada which is very close to yours truly's hometown Port Colborne, Ontario, Canada.