Most galaxies are moving away from us, and their receding speed (redshift) is proportional to the distance of the galaxies  The coefficient of this ratio is now called the Hubble constant, which represents the current rate of expansion of the universe  One of the core tasks of observational cosmology is to measure the relationship between distance and redshift  It describes the history of the expansion of the universe, answers basic questions about the age, geometry and composition of the universe, and even tests many new physical predictions
In astronomical observation, the redshift of distant celestial bodies can be obtained accurately, but the accurate measurement of distance has always been the biggest problem for astronomers
A breakthrough in measuring distance.