What spectral shift occurs when a galaxy moves away from the observer?
Answer
Redshift, where spectral lines shift toward the longer, redder end of the spectrum.
The phenomenon describing the change in observed wavelength of light due to relative motion between the source and the observer is the Doppler effect. When a light source, such as a distant galaxy, is moving away from the observer (receding), the light waves it emits are stretched. This stretching increases the wavelength of the observed light, causing the characteristic spectral lines—which correspond to specific elements like hydrogen or calcium—to shift toward the longer wavelength end of the electromagnetic spectrum. This shift towards the red end is universally termed a redshift, serving as the primary indicator of galactic recession velocities.
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