Doppler Effect, Astronomical Applications
A redshift is caused by the Doppler effect, which is the change in wavelength and frequency of either light or sound as the source and observer are moving either closer together or farther apart. In astronomy a redshift indicates that the source is moving away, and a blueshift indicates that the source is moving closer to us. Doppler shifts have many important applications in astronomy. They help us to deduce the masses of stars and of galaxies. The redshifts for the most distant objects in the universe tell us that the universe is expanding.