It is highly unlikely that Edwin Hubble would have been able to prove that the Universe consisted of more than the Milky Way had it not been for Henrietta Swan Leavitt, one of many rank amateurs who was hired by the Director of Harvard College Observatory, Edward C. Pickering, to sort through, and classify mountains of glass photographic plates.
By poring over thousands of glass plates, Leavitt discovered a new class of variable star called Cepheids in the Megallanic Clouds, and correctly deduced their distances by recognizing a correlation between their periods and luminosities.
It is a matter of historical record that Hubble used her discovery in 1929 to prove that the Universe contained huge numbers of what he termed “Island Universes”.
Although Leavitt discovered more than 2 400 variable stars, and was widely regarded as having the “best mind at the observatory” at the time, she died in 1921, never realizing that she had discovered the key to understanding the real size, complexity, and majesty of the Universe as we observe and understand it today.
Learn more about Henrietta Swan Leavitt on PBS