If a star is moving away from Earth, what happens to the light waves it emits?
Answer
The light waves are stretched, resulting in an increased wavelength.
When a star is receding from an observer, the light waves it emits are physically stretched out due to the relative motion away from the observer. This stretching increases the wavelength of the observed light. In the context of the visible spectrum, this results in a redshift, meaning the spectral features shift toward the longer, lower-energy red end of the spectrum. This stretching effect is the opposite of what occurs during approach, where the waves are compressed.
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Light and Motion: the Doppler Effect - YouTube
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