Description: The Doppler effect is the change in detected wavelength (or frequency) of sound or light waves caused by the relative motion of the source toward or away from the observer. This effect allows astronomers to study the motion of any body (stars, galaxies, gas, etc.) that emits waves (e.g. electromagnetic radiation). For example, in the case of radiation emitted from a star with spectral lines at specific wavelengths, the wavelengths of all the spectral lines will be shifted. For speeds significantly less than the speed of light, the Doppler shift in frequency (or wavelength) is proportional to the relative velocity of the source in the line of sight of the observer divided by the speed of light.

Related Terms:

• Electromagnetic Radiation
• Frequency
• Wavelength
• Blueshift
• Redshift

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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