Edwin Hubble was an American astronomer and cosmologist
Science - Astronomy
Edwin Hubble (1889-1963) was an American astronomer and cosmologist whose research found that the universe was ever expanding.
On December 30th, 1922, much like Copernicus in his time, Hubble challenged the status quo by announcing the existence of other galaxies in our solar system, beyond the Milky Way.
He observed the Cepheid variable and determined that its distance from Earth was too great to be part of the Milky Way, thus ending the existing debate on the subject.
This new understanding of the universe drastically changed how we study and classify astronomy.