Astronomers calculate speed of distant stars and galaxies using which of the following phenomena:

Explanation

The Doppler effect is a phenomenon where the observed frequency of a wave changes depending on the relative motion between the source of the wave and the observer. This effect is commonly used in astronomy to determine the motion of celestial objects, such as stars and galaxies.In the context of astronomy, the most common application of the Doppler effect is the redshift or blueshift of light. When a celestial object is moving away from an observer, its light is shifted towards longer wavelengths (redshift), and when it is moving towards the observer, the light is shifted towards shorter wavelengths (blueshift).Astronomers can measure these shifts in the spectrum of light emitted by stars or galaxies to determine their radial velocity (motion along the line of sight). This information is crucial for understanding the dynamics of galaxies, the expansion of the universe, and other aspects of celestial motion and structure. The redshift of light from distant galaxies played a key role in the discovery of the expansion of the universe.