A century ago, Edwin Hubble played a pivotal role in resolving astronomy’s ‘Great Debate’ regarding the nature of the universe and our cosmic neighborhood. This debate revolved around whether the Milky Way constituted the entirety of the universe or if there were other galaxies like our own lying beyond its bounds. The discussion was between the so-called “island universe” hypothesis, which posited that nebulae seen through telescopes were separate galaxies, and the opposing view, which suggested these “spiral nebulae” were merely part of the Milky Way.
The breakthrough came through Hubble’s meticulous observations at the Mount Wilson Observatory, where he utilized the then-revolutionary Hooker Telescope. His observations of Cepheid variable stars in the “Andromeda Nebula” provided the evidence needed to measure its distance accurately. Hubble’s findings showed that the Andromeda Nebula was far too distant to be within the Milky Way, proving it to be an entirely separate galaxy. This discovery fundamentally altered our understanding of the universe, establishing that the Milky Way is just one of countless galaxies within a vast cosmos. This monumental shift laid the groundwork for modern extragalactic astronomy and broadened the scope of the known universe.