Doppler effect is the change in frequency of sound, light, or radio waves caused by the relative motion of the source of the waves and their observer. For example, the pitch (frequency) of a train whistle seems higher when the train approaches and lower after it passes and begins to move away. The actual pitch of the whistle remains constant. Astronomers study the speed of a star by measuring the apparent change in the frequency of its light waves caused by motion. Christian Doppler, an Austrian physicist, described the effect in 1842.
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Doppler effect
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Doppler effect
See also Radar (Continuous-wave radar); Redshift; Sound (The Doppler effect); Sun (Doppler shift).
