It’s hard to overstate the impact of Edwin Hubble’s discovery 100 years ago: that the Milky Way is just one of countless galaxies scattered across the universe. This realization fundamentally reshaped our understanding of the cosmos. Here's a closer look at this historic moment:
### **A Century Ago: The Revolution Begins**
In the early 1920s, many astronomers believed that the universe was synonymous with the Milky Way. The term "nebula" was used to describe what we now know are other galaxies, and many thought these "nebulae" were simply distant parts of our own galaxy.
Hubble’s breakthrough came in **1924** when he identified **Cepheid variable stars** in the **Andromeda Nebula** (now the Andromeda Galaxy). By measuring the stars' brightness and period of variation, Hubble calculated their distance and demonstrated that Andromeda was far too distant to be part of the Milky Way. This proved that our galaxy is just one of many in the vast universe.
### **Hubble’s Methodology**
Hubble's discovery relied on the accurate measurement of distances to far-off objects, which was a major breakthrough in astronomy. Before his work, no one had been able to accurately measure the distances to galaxies outside the Milky Way. His observations used Cepheid variables as "standard candles," a technique still fundamental in cosmology today.
### **The Expanding Universe**
This discovery set the stage for another of Hubble’s groundbreaking insights—the realization that the universe is **expanding**. By analyzing the redshifts of galaxies, Hubble demonstrated that galaxies move away from each other at speeds proportional to their distance. This observation, published in 1929, eventually led to the formulation of the **Big Bang Theory**.
### **The Impact and Legacy**
Hubble’s revelation not only expanded our view of the universe but also shifted the framework of modern cosmology. The idea that the universe consists of billions of galaxies, each potentially with its own stars and planetary systems, radically transformed humanity’s place in the cosmos.
Today, we continue to explore the universe through tools like the **Hubble Space Telescope**, which builds on Hubble's discoveries. It has opened windows into the early universe, the formation of galaxies, and the mysterious dark matter and dark energy that shape the cosmos.
For more information, you can check out EarthSky’s tribute to Edwin Hubble and his legacy.
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