Christian Doppler first proposed the effect in 1842. He presented the idea in a paper titled “Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels,” concerning the colored light of binary stars and other stars.
Doppler argued that the observed frequency of a wave should change when the source and observer move relative to each other. He imagined that this could explain differences in the apparent colors of binary stars, although his original explanation of stellar colors was not fully correct. The broader wave principle itself was sound and later became known as the Doppler effect.
The hypothesis was tested for sound in 1845 by Dutch scientist Christoph Buys Ballot, who used musicians on a moving train to demonstrate changes in perceived pitch. French physicist Hippolyte Fizeau independently applied the idea to electromagnetic waves in 1848. Some historical sources mention 1843 because of publication details, but 1842 is the standard year for Doppler’s original proposal.