Expanding Universe
Year of Discovery: 1926
What Is It? The universe is expanding. The millions of galaxies move ever
outward, away from its center.
Who Discovered It? Edwin Hubble
Why Is This One of the 100 Greatest?
Hubble’s twin discoveries (that there are many galaxies in the universe—not just the
Milky Way—and that all of those galaxies are traveling outward, expanding the universe)
rank as the most important astronomical discoveries of the twentieth century. These discoveries radically changed science’s view of the cosmos and of our place in it. Hubble’s work
also represents the first accurate assessment of the movement of stars and galaxies.
The discovery that the universe is expanding and ever changing for the first time allowed scientists to ponder the universe’s past. This discovery led directly to the discovery
of the Big Bang and the origin of the universe as well as to a new concept of time and of the
future of the universe.
How Was It Discovered?
In 1923 Edwin Hubble was a tall, broad-shouldered, powerful astronomer of 33 who,
10 years earlier, had almost chosen a career as a professional boxer over astronomy. Hubble
had been hired in 1920 to complete and operate the Mt. Wilson Observatory’s mammoth
100-inch telescope in California—the largest telescope in the world.
In the early twentieth century, the universe was thought to contain one galaxy—the
Milky Way—plus scattered stars and nebulae drifting around its edges. Hubble decided to
use the giant 100-inch telescope to study several of these nebulae and picked Andromeda as
his first target—and he made the two most important astronomical discoveries of the
twentieth century.
This giant telescope’s power showed Hubble that Andromeda wasn’t a cloud of gas (as
had been thought). It was a dense cluster of millions of separate stars! It looked more like a
separate galaxy.
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