Hubble Showed Other Galaxies Exist Beyond the Milky Way

For centuries, astronomers argued over the faint smudge of light called the Andromeda Nebula. Was it a cloud of gas inside our Milky Way, or a separate “island universe” far beyond it? In 1923, working with the 100-inch Hooker telescope at Mount Wilson Observatory, Edwin Hubble found the answer hiding in a single point of light.

Hubble spotted a Cepheid variable star, later named V1, pulsing in brightness like a slow heartbeat. Because Cepheids brighten and dim on a clock tied to their true luminosity, he could measure its distance. The star sat about 1 million light-years away, far outside the Milky Way’s known span.

Andromeda was not a cloud within our galaxy. It was a galaxy of its own.

On November 23, 1924, the New York Times became the first publication to report Hubble’s discovery. His formal paper followed weeks later. In a single stroke, the cosmos expanded from one galaxy to an ocean of them, reshaping humanity’s place in the universe.