Edwin Hubble's research into the Andromeda Nebula commenced in the early 1920s while he was utilizing the powerful 100-inch telescope at Mount Wilson Observatory in California. Through meticulous observations, Hubble identified Cepheid variable stars within the Andromeda Nebula, which allowed him to calculate its distance from Earth. Previously, the prevailing view among astronomers was that the nebulous objects in the sky were simply part of the Milky Way. However, Hubble's calculated distance revealed that Andromeda was over two million light-years away, thereby establishing it as a separate galaxy, an 'island universe' in its own right.

In November 1924, Hubble's revolutionary findings were published in The New York Times, capturing the attention of both the scientific community and the public. His conclusion not only redefined the Milky Way's boundaries but also elevated the status of other galaxies as unique systems, contributing to the eventual formulation of the modern understanding of an expanding universe. This marked a significant turning point in cosmology, prompting scholars to rethink previous models of the universe.

Hubble’s discovery laid the foundations for modern astrophysics, as scientists began to explore the vastness of space beyond the Milky Way. The concept of galaxies as independent systems, rather than mere components of a larger cluster, has had profound implications for the field of astronomy and science at large, leading to developments in theoretical physics and the understanding of the universe’s structure, culminating in the Big Bang theory and redshift observations that signify an expanding universe.