ABSTRACT
The Doppler effect is a well-known phenomenon: the sound of a train whistle has a higher pitch when the train is traveling toward the listener than when moving away, though the emitting frequency remains the same. In 1842, the Austrian physicist Johann-Christian Doppler, studying the direction of movement of stars, mathematically described this frequency shift of recorded waves when a luminous or acoustic source, in relative motion, is compared with the stationary observer.
