Whose astronomical observations finally proved the Milky Way was just one of many galaxies in the universe?

The Milky Way is the galaxy that contains our solar system. The descriptive "milky" is derived from the appearance from Earth of the galaxy- a band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term "Milky Way" is a translation of the Latin 'via lactea' originating from the Greek 'galaxias kyklos' translated 'milky circle'.

From Earth, the Milky Way appears as a band across the night sky because of its disk-shaped structure when viewed from within. Galileo Galilei first proved the band of light to be individual stars with his telescope in 1610. Until the early 1920's, most astronomers thought that the Milky Way contained all the stars in the universe.

Following the 1920 great debate between astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies. It is now known that the Milky Way is only one of an estimated 200 billion or more galaxies.