One of the most groundbreaking discoveries in modern astronomy came 100 years ago when Edwin Hubble, an American astronomer, made a revelation that changed our understanding of the universe forever. Before his work, it was widely believed that the Milky Way was the only galaxy in existence, with all stars and celestial objects contained within it. However, Hubble’s observations in the early 20th century provided concrete evidence that the universe is far more vast and complex than anyone had previously imagined.

In 1924, using the powerful Hooker Telescope at the Mount Wilson Observatory in California, Hubble observed the Andromeda Nebula (now known as the Andromeda Galaxy). By analyzing the light emitted from the nebula, he discovered that it contained stars that were moving away from Earth at great speeds. This was a clear indication that the Andromeda Nebula was not part of the Milky Way, but a separate galaxy altogether.

Hubble’s work on the Andromeda Galaxy was crucial, but it was his discovery of the "redshift" in the light from distant galaxies that truly revolutionized astronomy. By observing the spectral lines of galaxies, Hubble found that most galaxies were moving away from the Milky Way, which led him to propose that the universe was expanding. This discovery laid the foundation for what would later become known as Hubble’s Law, stating that the farther a galaxy is from Earth, the faster it is receding from us.

Hubble’s findings not only confirmed the existence of countless other galaxies but also forever altered the course of cosmology. His contributions to science opened the door to modern astrophysics, and his work remains fundamental in our understanding of the universe today.