The red shift is also called red shift , is and blue shift Relative physical phenomenon refers to Spectral line Moved a distance relative to the direction of the observer toward the red end. 
Red shift Doppler redshift : The relative motion between the object and the observer can cause redshift, and the corresponding redshift is called Doppler redshift, which is caused by the Doppler effect. Gravitational redshift According to the general theory of relativity, light will also redshift when it is emitted from the gravitational field. This redshift is called gravity redshift.
Cosmological redshift At the beginning of the 20th century, Edwin Hubble, an American astronomer, found that the spectral lines of most galaxies in the universe have redshifts. This kind of redshift is caused by the expansion of the universe and the extremely high retrogression speed of the galaxy relative to the observer, which is called the cosmological redshift. And then Hubble's law is obtained. In the 1960s, a class of celestial bodies with extremely high redshift was discovered—— a quasar And became a very active research field in modern astronomy. 
