The Doppler effect changes the observed frequency of a wave when source and observer move relative to one another. For light and a small radial recession speed , , where is wavelength. This is the basis of Doppler spectroscopy.
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The Doppler effect is a phenomenon observed when the source of a wave (such as sound or light) is moving relative to an observer. It describes the change in frequency (or wavelength) of the wave as perceived by the observer due to the relative motion. 1. **Sound Waves**: When a sound source moves towards an observer, the sound waves get compressed, resulting in a higher frequency (or pitch) of the sound.