The Universe

Evolution of the Universe

How does the Doppler effect work for light?

When an object emitting light—or any kind of electromagnetic radiation, for that matter—moves toward someone, the wavelength of its emitted light is decreased. Conversely, when the object moves away, the wavelength of its emitted light is increased. For visible light, the bluer part of the spectrum has shorter wavelengths, and the redder part of the spectrum has longer wavelengths. Thus, the Doppler effect for light is called a “blueshift” if the light source is coming toward an observer, and a “redshift” if it is moving away. The faster the object moves, the greater the blueshift or redshift.


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