What phenomenon results when spectral lines shift toward the red end because a galaxy is moving away?
Answer
Redshift
Redshift occurs when the source of light, such as a distant galaxy, is moving away from the observer. This recession causes the light waves emitted by the source to be stretched as they travel across space toward the observer. This stretching increases the wavelength of the observed light, shifting the characteristic spectral lines toward the lower frequency, longer wavelength end of the spectrum, which corresponds to the color red. This is contrasted with blueshift, where movement toward the observer compresses the wavelengths toward the blue end. The measurement of this redshift, denoted as $z$, is directly proportional to the recessional velocity.
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