Relating to the change in frequency of waves (sound, light, radio) from a source moving relative to an observer.
Named after Austrian physicist Christian Doppler (1803-1853), who first described the effect in 1842. His surname derives from German 'Toppler,' meaning someone who lived by a hill or worked as a potter.
The Doppler effect explains why ambulance sirens change pitch as they pass by, but it also enables radar technology and helps astronomers measure the expansion of the universe. Doppler's original paper was about the colors of binary stars, not sound at all!
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