Largest telescope in the world

The Calif. observatory that changed how we think about the universe

One man's quest to build the largest telescope in the world, again and again

By Erin Rode

On Jan. 1, 1925, astronomer Edwin Hubble completely changed the way we view the universe and our place in it. The discovery came from peering through what was then the world’s largest telescope, located on a remote mountaintop in Angeles National Forest. Not only was the view world-altering, but it was also life-changing for Hubble, who became one of the most well-known names in astronomy. Today, even the most casual of space observers are likely familiar with his name.

But Hubble’s major discovery is arguably (at least partially) due to the efforts of a slightly lesser-known astronomer: George Ellery Hale, a man determined to build the largest telescope in the world on a mountain summit high above, of all places, the then-burgeoning city of Los Angeles.

One man’s quest to build huge telescopes

Hale’s obsession with building bigger and bigger telescopes began on a trip to the Bay Area’s Lick Observatory in 1890, which housed a 36-inch refractor, at the time the largest telescope on Earth. Within a few years, Hale had raised the funds for a 40-inch telescope of his own, to be placed at the Yerkes Observatory in Wisconsin, where he was the director. 

In 1903, Hale visited Mount Wilson, a 5,715-foot summit in the San Gabriel Mountains above Pasadena, and was enamored with the possibility of a mountaintop observatory in California’s milder climate. “The isolation of the mountain top . . . made a strong appeal to [Hale’s] pioneering spirit and his joy in the discoveries of the ever-changing beauties in nature,” wrote one of the observatory’s first staff members around that time. 

Hale moved a solar telescope from the Yerkes Observatory west to Mount Wilson, and the Mount Wilson Solar Observatory (now known as the Mount Wilson Observatory) was formed in 1904. 

Hale quickly got to work building an even bigger telescope on Mount Wilson than he’d had back in Wisconsin, and in December 1908, a new 60-inch telescope was used for the first time, dwarfing the Lick Observatory he had first encountered nearly 20 years before. The 60-inch figure refers to the diameter of the circular disk of glass used to gather and reflect light from space; the more inches, the more that observers can clearly see and document. 

Hale was a prolific fundraiser, networking and advocating for more funding for astronomy with some of the wealthiest magnates of the era, including Andrew Carnegie, so it was only natural that before long, Hale had raised enough capital to fund a telescope even larger than 60 inches. In fact, Hale had already started building his next even bigger telescope before the 60-inch was in operation. 

Efforts to complete a new 100-inch telescope carried on for over a decade, amid many doubts that it would work and a stressful flurry of fundraising by Hale, who fell into poor health. Worried about Hale’s constant stress over the telescope, his wife once wrote, “I wish that glass was in the bottom of the ocean.”

Once placed inside its large white dome, the mirror was ready for its first viewing. A crowd of astronomers and others gathered to try to catch a glimpse of Jupiter through the telescope. Instead, the view through the eyepiece was warped, showing “six or seven partially overlapping images irregularly spaced and filling much of the eyepiece,” wrote Walter Adams, the observatory’s assistant director. But the problem was simple: Since the dome was left open during the day, the mirror got too hot, expanding the glass surface and warping the resulting image. Hale and Adams returned to the dome at 3 a.m. and got their first clear glimpse of the stars through the giant telescope. 

Settling the question of distant ‘island universes’

Mount Wilson’s huge, cutting-edge telescopes drew Edwin Hubble to the observatory in 1919, where he’d go on to make one of his biggest discoveries.

At the time, the astronomy community was focused on the question of “spiral nebulae,” which look like cloudy pinwheels of stars in the sky, and whether these spirals were part of our Milky Way galaxy or their own “island universes.”

Using the 100-inch telescope, Hubble looked for stars of varying brightness in one such area, the Andromeda Nebula, where he found one type of star that was helpful in determining distance. By finding dozens of these stars in different spiral nebulae, and by focusing on individual stars instead of only looking at the spirals as a whole, Hubble eventually determined that the nebulae were too far away to be within the Milky Way. 

In that discovery, the entire way we think about the universe shifted. There wasn’t one galaxy, dominated by the Milky Way and surrounded by more distant spiral nebulae, but many far-off galaxies in addition to the Milky Way. The realization vastly expanded our understanding of the size of the universe.  

Hubble’s findings “proved beyond question that nebulae were external galaxies comparable to our own. It opened the last frontier of astronomy, and gave, for the first time, the correct conceptual value of the universe. Galaxies are the units of matter that define the granular structure of the universe,” wrote Allan Sandage in the Hubble Atlas of Galaxies. 

“The whole proceeding illustrates admirably how the scientist works. He has an open mind. He is always ready to adopt the theory which facts seem best to support. He is ready to change his opinion when new facts justify it,” wrote one journalist in the Whittier News shortly after the discovery. 

Telescopes for the people

Today, the white domes of Mount Wilson’s telescopes are still viewable from the 210 freeway below on clear days, while the forested grounds on the summit are pretty quiet most days save for day-trippers, hikers and occasional afternoon concerts. Hints at the observatory’s importance are present throughout the meandering facilities, from a tiny sign that reads “EINSTEIN WAS HERE! January 29, 1931” tacked to the wall inside the 150-foot solar telescope to the locker with Hubble’s name on it below the 100-inch telescope. 

The observatory is now run largely by volunteers with the Mount Wilson Institute, with a mission of connecting the public to space at the observatory. This mission has included launching public events beneath the 100-inch telescope, hosting lectures, facilitating group rentals of the 60-inch and 100-inch telescopes, and hosting public ticket nights, when individuals can buy a ticket and look through the telescopes. The observatory still looms over Los Angeles, after just narrowly surviving the 2020 Bobcat Fire, which burned surrounding portions of Angeles National Forest and came within a few hundred feet of the famed telescopes. 

And while they’re no longer the world’s largest, the observatory’s telescopes still hold a superlative claim to fame that Hale might be proud of. According to the observatory, the telescopes now hold the title of the “largest telescopes in the world that are available for public use.”