Mount Wilson Observatory

Less than 100 years ago, many scientists thought that our Milky Way galaxy was the entire universe. Then, in the 1920s, astronomers at California's Mt. Wilson Observatory forever changed this view of the universe. Using the world's largest telescope, Edwin Hubble and his team discovered the first galaxies beyond our own. Then they found that other galaxies were moving away from us, the first solid evidence that the universe is expanding.

Location: Mount Wilson, San Gabriel Mountains, near Los Angeles, California
Founded: 1904 by George Ellery Hale
Claim to Fame: held the world's largest optical telescope for 40 years
Major Discoveries: sunspots, first galaxies, expansion of the universe
Cool Fact: The route to the top of Mt. Wilson was so steep and dusty, mules had to carry materials to build the observatory and its telescopes.

Image credits: main image, © AMNH.