By Brandon Gage
It was October 6, 1923. Perched atop Mt. Wilson in Pasadena, California, Edwin Hubble peered through the 8-meter telescope that at the time was the most advanced in the world. What he found changed our understanding of the Universe and our place in it.
For ages, fuzzy blobs called “nebulae” had perplexed astronomers. They were clearly not stars, but they peppered the night sky in a number of constellations. One such nebula was in the constellation Andromeda.
Hubble aimed his telescope at an otherwise unremarkable patch of sky, and what he saw astonished him. That tiny, blurry blob turned out to be a swirling disc of a trillion stars, gas, and dust. Hubble quickly realized it could be an entire galaxy - which at the time, was a revolutionary idea. Up until that day, the Milky Way was the whole Universe.
Hubble knew he was onto something. The Andromeda cloud was huge, and therefore, must be incredibly distant. Using light from a supernova that he spotted on the edge of Andromeda, Hubble was able to estimate its distance. His guess was 800,000 light years (he underestimated, however, as Andromeda is really two million light years away). From this, Hubble was able to conclude that Andromeda - and therefore every other one of the nebulae that had puzzled scientists - were whole galaxies separate from our own.
Literally overnight, humanity’s view of the Universe was shattered. The Milky Way became just one of trillions of galaxies - island Universes - each containing hundreds of billions of stars.
But Hubble wasn’t finished. He noticed that some of the light from distant galaxies was slightly reddish, which meant they were moving away from us. Over many months, Hubble was able to measure this effect, called red shift, and discovered that the Universe is expanding.
This turned cosmology on its head. The top scientific minds at the time, including Albert Einstein, believed the Universe was eternal, and on large scales, unchanging. Hubble’s discovery led to the inevitable conclusion that the Universe had a beginning, and therefore, a finite age.
Within the next decade, theories about the birth of the Universe emerged. The leading contender was named “Big Bang.” 13.77 billion years ago, all time, space, and matter exploded into existence from an infinitesimally small and dense point. How and why this happened remains a mystery, but we know it occurred because of the residual heat - the Cosmic Microwave Background - which is spread across the cosmos.
Hubble’s name would later adorn the most famous telescope ever built, which orbits the Earth 350 miles above our heads. His legacy - arguably as the greatest observational astronomer in history - has fueled insights into our Universe that have defied comprehension.