Doppler Effect in Astronomy

The Doppler effect has become one of the most powerful tools astronomers use in the study of the universe.
Assuming that distant stars and galaxies are made up of the same matter as nearby stars, we can compare the spectral lines emitted by distant galaxies with the corresponding spectral lines radiated by elements here on earth. A general shift in the wavelengths to the blue or the red, indicates that the source of the waves is moving either toward or away from us. Using Equations (1) we can then quite accurately determine how fast this motion toward or away from us is.

Until the 1960s astronomers did not have much need for the relativistic Doppler shift equations. The non relativistic Equations (2) were generally adequate because we did not observe stars or galaxies moving relative to us at speeds greater than 10 to 20% the speed of light. But that changed dramatically with the discovery of quasars in 1963. Quasars are now thought to be brilliant galaxies in the early stages of formation. They can be seen from great distances and are observed to move away from us at speeds as great as 95% the speed of light. 

........(1)

.......(2)