When light from a distant, receding galaxy is observed, how do its wavelengths change, and what is this phenomenon called?

Answer

Wavelengths are stretched toward the red end; Redshift.

As a light source moves away from an observer, the wavelengths of its emitted light are stretched, causing them to shift toward the longer, redder end of the electromagnetic spectrum.

When light from a distant, receding galaxy is observed, how do its wavelengths change, and what is this phenomenon called?

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