One hundred years ago, on November 23, 1924, a groundbreaking discovery reshaped our understanding of the universe.
A small article in The New York Times revealed that Dr. Edwin Hubble had confirmed that the Milky Way was not the only galaxy in the cosmos.
This revelation opened the door to understanding the vastness of space and the countless galaxies that fill it.
For years, scientists debated whether the universe consisted only of the Milky Way or if other “island universes” existed. In 1920, a famous event called “the great debate” took place.
Astronomer Harlow Shapley argued that spiral-shaped nebulae (cloud-like formations of gas and stars) were part of the Milky Way, while Heber Curtis claimed they were separate galaxies.
In 1924, Hubble settled the debate. Using the powerful Hooker telescope at Mount Wilson Observatory near Los Angeles—the largest telescope of its time—he studied two spiral nebulae, now known as the Andromeda Galaxy and Messier 33.
By measuring the brightness of certain stars within them, Hubble proved they were far beyond the boundaries of the Milky Way. These objects were galaxies of their own.
Hubble’s discovery was possible because of earlier work by astronomer Henrietta Swan Leavitt.
In 1912, Leavitt found that certain stars, called Cepheid variables, pulse in brightness over time. The slower the pulse, the brighter the star.
This “period-luminosity relationship” allowed astronomers to calculate distances to these stars.
By identifying a Cepheid variable in Andromeda and applying Leavitt’s findings, Hubble determined that the galaxy was much farther away than the Milky Way’s boundaries.
His measurements were confirmed by tools like stellar parallax, which estimates distances to nearby stars based on their apparent movement in the sky.
Hubble’s discovery was a turning point in astronomy, but it was just the beginning.
Using data from other astronomers, like Vesto Slipher, who measured the speeds of galaxies, Hubble uncovered another key insight: the universe is expanding.
Slipher had found that most galaxies were moving away from Earth, as shown by a phenomenon called redshift. This shift in light waves is similar to how a siren’s pitch changes as it moves past you.
By combining distance measurements with galaxy speeds, Hubble observed that galaxies farther from Earth were moving away faster. This discovery laid the foundation for the Big Bang theory, which describes how the universe began from a single point and has been expanding ever since.
Hubble’s work revolutionized our understanding of the universe.
Today, we estimate there are trillions of galaxies. His name lives on through the Hubble Space Telescope, which continues to capture stunning images and provide insights into the cosmos.
This monumental discovery, made just a century ago, reminds us of how far we’ve come in exploring the mysteries of the universe—and how much there still is to learn.
Source: The Conversation.
