Mount Wilson, spectacularly perched over the Los Angeles basin high above Pasadena, has a rich astronomical history.
In the 1880s, scientists noticed that most of the time the San Gabriel Mountains, and Mount Wilson, had the astronomically desirable qualities of a clear sky and stable night air.
In 1889 USC President Marian Bovard ordered the glass for a 40-inch refracting telescope to be paid for with a $50,000 gift from a local banker. Bovard hoped that USC would soon operate the world’s largest telescope and share a site on Mount Wilson where Harvard would also establish an observatory.
Harvard astronomers installed a 13-inch refracting telescope on the mountain only to suffer through the winter of 1889-90, one of the severest on record. At the same time, the Southern California economy foundered and the gift to pay for USC’s telescope did not materialize.
The glass for the telescope, however, had already been ground. George Ellery Hale, a young, unknown Chicago astronomer, heard about the glass and persuaded the University of Chicago and streetcar magnate Charles Yerkes to back him. The telescope ended up at Lake Geneva, Wis., where Hale be came the first director of the Yerkes Observatory.
Mount Wilson soon captivated Hale. He ended up building the world’s largest telescope three more times and two of them, the 60-inch and 100-inch reflectors, are still in use on Mount Wilson.
In 1908, Hale built the 60-foot tower that USC operates today, and in the first year of its operation discovered the sun’s magnetic field. In the early 1960s, Robert Leighton, a Cal tech physicist, used the facility to show that the sun vibrates with a predominant period of five minutes. The sun’s surface appears roiling and disorganized, like boiling water, but Leighton determined that waves periodically pulsed out to a peak and then collapsed back into the interior.
“These were the two key discoveries made at the 60-foot tower,” said Ed Rhodes, professor of physics and astronomy who is in charge of the facility today. “In the late ’70s, I learned that the tower was only being used for about 40 minutes a day and was able to secure it for this project” (studying solar oscillation patterns).
The tower is actually a large coelostat, which is a device with flat mirrors that reflect sunlight through a stationary lens to form images. Before Hale, coelo stats were much smaller and usually rigged temporarily for studying solar eclipses.
Hale, who wanted to study the sun, was frustrated that only relatively small instruments could be attached to the moveable ends of telescopes. He wanted to use large spectrographs to spread the spectrum of sunlight wider so he could make a more detailed study.
“There’s a 30-foot working spectrograph underneath this tower,” said Rhodes. “When it was built, this was the world’s premier tool for solar research. We still find that much of the old original equipment works better than the newer stuff.”
While there are almost 300 clear days per year in which Rhodes can study the sun, the top of Mount Wilson – slightly more than a mile above sea level – can still be subject to the rain, snow and cold that drove Harvard away.
“When I first came here in 1968 we sometimes wore heated flight suits,” Rhodes said. “Milton Humason [an astronomer with no formal training who started at Mount Wilson as a janitor] was famous for the fur coats he wore.”
The 60-foot tower was not state-of-the-art for long. Almost immediately after discovering the sun’s magnetic field, Hale began work on an adjacent 150-foot tower that is today operated by UCLA. In 1931, Albert Einstein visited the 150-foot tower where the solar astronomers were involved in an unsuccessful attempt to gather evidence to support his theory of general relativity.
“They were trying to measure the red shift caused by the gravitational field of the sun,” said Rhodes. The theory, since proven, holds that a light beam from a distant star would bend as it passed through the strong gravitational field of the sun. “There are so many other motions in the sun that the sun turned out not to be the best star test to use.” In fact, the gravitational red shift was not observed until 1954 using the light from a white dwarf star.
Using Mount Wilson’s 100-inch telescope, Caltech astronomer Edwin Hubble showed that the universe is expanding, a discovery that Stephen Hawking described in his recent USC lecture as the greatest scientific achievement of the 20th century.
In the beginning, astronomical equipment was hauled up Mount Wilson by mules. Today, you can visit the Mount Wilson Observatory by following the Angeles Crest Highway north of La Canada Flintridge for 14 miles to Red Box Road. Turn right and go another 5 miles to the observatory gate. The observatory has walking tours on weekends, picnic facilities and a visitor’s center. More information is available at http://www.mtwilson.edu/