Final answer:
A galaxy moving away from us has a redshifted spectrum due to the Doppler effect, where light waves stretch, increasing their wavelength.
A galaxy moving towards us would have a blueshifted spectrum. These shifts provide valuable information about galaxy movement and the universe's expansion.
Step-by-step explanation:
If a galaxy is moving away from us, its spectrum is not blueshifted, but rather redshifted. This phenomenon, known as the Doppler effect, occurs because the light waves stretch out as the galaxy moves away, increasing their wavelengths, which corresponds with the red end of the visible light spectrum.
Conversely, if a galaxy were moving toward us, its spectrum would be blueshifted because the light waves would be compressed, leading to shorter wavelengths that fall closer to the blue end of the spectrum.
This principle helps astronomers determine the movement of galaxies and understand the expansive nature of the universe.
In a practical sense, each galaxy's spectrum is a composite of its stars, some moving toward and others moving away from us. This can result in a range of Doppler shifts within the galaxy, known as line broadening. This information about line broadening and motion can be used to calculate important properties like the galaxy's mass.
Furthermore, in cosmology, the redshift of a galaxy's spectrum is also interpreted as evidence of the expansion of space itself, rather than just the motion of the galaxies through space. This expansion of space causes the wavelengths of light to stretch, leading to the observed redshifts.