Edwin Hubble Announced Other Galaxies Exist
On this day · 30 December 1924
On the last days of 1924, one astronomer's measurements quietly expanded the known universe from a single galaxy to countless ones.
On December 30, 1924, the work of astronomer Edwin P. Hubble was presented to a meeting of the American Astronomical Society in Washington, revealing that our Milky Way is just one of many galaxies in the universe. For the first time, the cosmos was shown to be vastly larger than anyone had proven.
Using the 100-inch Hooker Telescope at Mount Wilson Observatory, Hubble had spotted faint pulsing stars called Cepheid variables inside the Andromeda Nebula. Because a Cepheid’s pulse rate reveals its true brightness, he could gauge its distance, finding Andromeda lay far beyond our own galaxy’s edge. The fuzzy “nebula” was a separate island universe of its own.
A single class of star turned a smudge of light into a galaxy hundreds of thousands of light-years away.
Hubble’s result settled the long-running “Great Debate” over whether spiral nebulae sat inside the Milky Way or stood apart. His finding reframed humanity’s place in a universe filled with galaxies and laid the groundwork for modern cosmology and the discovery of cosmic expansion.
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