Alongside extragalactic astronomy, what field did Edwin Hubble help establish?

Alongside extragalactic astronomy, Edwin Hubble helped establish observational cosmology. This field studies the universe as a whole through measurable evidence, including galaxy distances, redshifts, large-scale structure, and the history of cosmic expansion.

Hubble's work at Mount Wilson connected two crucial observations. Cepheid variables provided distance estimates for galaxies beyond the Milky Way, while earlier measurements by Vesto Slipher supplied many galaxy redshifts. In 1929, Hubble published evidence that more distant galaxies generally had larger recession velocities, a relationship later called Hubble's law. It became a major observational foundation for modern cosmology.

The result did not mean Hubble single-handedly invented the expanding-universe idea. Georges Lemaître had derived and published a distance–velocity relationship in 1927 from general relativity, before Hubble's 1929 paper. Hubble's importance was in assembling influential astronomical observations that helped establish the universe's enormous scale and apparent expansion as central cosmological questions.