How did Edwin Hubble show that the universe is expanding?

American astronomer Edwin Hubble demonstrated that the universe is expanding by establishing a linear relationship between the distance of galaxies and their redshift.12

Working with Milton Humason, Hubble combined his own distance measurements—derived from observing Cepheid variable stars—with spectral shift data, which had been pioneered by Vesto Slipher. In 1929, Hubble published findings showing that the more distant a galaxy is from Earth, the faster it appears to be receding, a phenomenon now known as Hubble’s law.2314

This relationship is expressed by the formula:
$$\text{velocity}=H_0\times \text{distance}$$
where $H_0$ is the Hubble constant. By interpreting these redshifts as a consequence of motion, astronomers concluded that the universe is not static but is undergoing a large-scale expansion. This discovery provided the first observational evidence for the expanding universe model, a concept that remains fundamental to modern cosmology.2541