Mount Wilson Observatory

Los Angeles, California

Mount Wilson Telescope Receives APS Historic Site Plaque

By David Voss

APS selected the world-famous 100-inch Hooker telescope at the Mount Wilson Observatory in the San Gabriel Mountains of Los Angeles, California, as one of its Historic Sites. At a ceremony in October, 2019 APS President David Gross presented a plaque marking the site as the place where astronomers Edwin Hubble, Milton Humason, and Walter Baade made world-changing discoveries about the cosmos.

The observatory was founded in 1904 by George Ellery Hale (then-director of the Yerkes Observatory at the University of Chicago) with funding and support from the Carnegie Institution for Science. In 1906, John Hooker, a Los Angeles industrialist and amateur scientist, gave Carnegie a grant of $45,000 to purchase a 100-inch glass mirror for a large reflecting telescope. The Hooker telescope was completed in 1917 and was the largest optical telescope until 1948 when the 200-inch Hale Telescope was built at Palomar Observatory.

The plaque recognizes a number of seminal discoveries made with the telescope. Hubble joined the Carnegie Institution staff in 1919 and, while working at Mount Wilson, he showed that objects like Andromeda were entire galaxies outside the Milky Way. He and his assistant Humason discovered a linear relationship between the distances of galaxies and how fast they are moving away from Earth, evidence for an expanding universe.

Another astronomer working at Mount Wilson, Walter Baade, studied the stars in the Andromeda galaxy and classified them into different groups based on their age and elemental constituents. This allowed him to make a more accurate estimate of the size and age of the universe.

Mount Wilson Observatory continues as a center of astronomy outreach and the Hooker telescope can be reserved for use by the public. The observatory continues to be owned by the Carnegie Institution and is operated by the Mount Wilson Institute. For more information visit the Mount Wilson Observatory website.

The APS Historic Sites Initiative was created by the APS Executive Board in October 2004 with the mission to raise public awareness of physics. To date, almost 50 sites around North America have been honored with this designation. For more information about the initiative, please visit the APS Historic Sites page.

Presentation at Mt. Wilson
Keida Mascaro

2019 APS President David Gross (R) presents the Historic Site plaque to Thomas Meneghini (L), Executive Director of the Mount Wilson Institute.

Hooker Telescope at Mt. Wilson
Craig Baker/Wikimedia Commons

Dome containing the 100-inch Hooker Telescope.