An object emitting waves while remaining stationary to an observer. As the waves move toward the observer on the left, they undergo a blueshift. As the waves move away the observer on the left, they undergo a redshift.

The Doppler Effect refers to perceived changes in electromagnetic radiation emitted by objects moving through space. As a light source approaches, there is an increase in its measured frequency. This apparent increase is known as a blueshift. Conversely, as a wave emitting object moves away from an observer, the wavelengths have a longer interval between them, and are thus said to be redshifted. By applying the Doppler Effect to the observation of stars and their electromagnetic spectrum, astronomers are able to determine their distance and motion relative to Earth.