The astronomical term "nebulae," Hubble explained, had come down through the centuries. It was the name given to permanent, cloudy areas in the sky outside our solar system. Some astronomers thought nebulae were part of our Milky Way galaxy. Others thought they were island universes farther away in space. In his research paper, Hubble said the issue could be decided only by more powerful instruments. And those instruments had not yet been developed.
In nineteen seventeen, the United States was fighting in World War One in Europe. Edwin Hubble joined the American army and served in France.
Earlier, astronomer George Ellery Hale had offered Hubble a position at the Mount Wilson Observatory in Southern California. When Hubble returned to the United States after World War One, he accepted Hale's offer. Hubble was thirty years old. He was just beginning the work that would make him famous.
In his first observations from Mount Wilson, Hubble used a telescope with a mirror one hundred fifty-two centimeters across. He studied objects within our own galaxy. And he made an important discovery about nebulae.
Hubble said the light that appeared to come from nebulae really came from stars near the nebulae. The nebulae, he said, were clouds of atoms and dust. They were not hot enough -- like stars -- to give off light.
Soon after, Hubble began working with a larger and more powerful telescope at Mount Wilson. Its mirror was two hundred fifty centimeters across. It was the most powerful telescope in the world for twenty-five years. It had the power Hubble needed to make his major discoveries.
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