On September 13, 1922, a groundbreaking discovery was made by American astronomer Edwin Hubble. While observing the night sky at the Mount Wilson Observatory in California, Hubble spotted a Cepheid variable star in the Andromeda Nebula (now known as the Andromeda Galaxy).

Cepheid variable stars are a special type of star that pulsates in brightness at a regular interval. The period of their pulsation is directly related to their intrinsic luminosity, making them excellent "standard candles" for measuring cosmic distances.

Using the 100-inch Hooker Telescope, the most powerful telescope at the time, Hubble meticulously studied the Cepheid variable he had found. After careful calculations, he determined that the Andromeda Nebula was not a gaseous cloud within our own Milky Way Galaxy, as previously believed, but rather a separate galaxy far beyond the confines of our own.

This revelation sent shockwaves through the astronomical community. Hubble's discovery provided the first conclusive evidence that the universe extended far beyond the Milky Way, and that countless other galaxies existed in the vast expanse of space.

Hubble's finding marked a turning point in our understanding of the cosmos. It opened the door to the concept of an expanding universe and laid the foundation for the Big Bang theory. Today, the Hubble Space Telescope, named in honor of Edwin Hubble, continues to unravel the mysteries of the universe, building upon the groundbreaking work of its namesake.

So, the next time you gaze up at the night sky and spot the faint, fuzzy patch of the Andromeda Galaxy, remember the remarkable discovery made by Edwin Hubble on this day in 1922 – a discovery that forever changed our perception of the universe and our place within it.