The Great Dome

Before the early film impresarios set up shop here for the constant sunshine - a full decade, in fact, before Carl Laemmle’s 230-acre chicken ranch became Universal City - someone had already noticed the light in Los Angeles. That someone was George Ellery Hale, an astronomer from back East who had developed a way to photograph the sun. Hale studied the sun daily, so he needed good light. And in 1904 he built a big version of his spectroheliograph atop Mount Wilson, about 10 miles northeast of Los Angeles, to take advantage of the calm air and the 300 cloudless days the area gets each year. The site grew, with four more telescopes added over the next decade and a half, the last of which was the Hooker 100-inch - then the largest in the world, and the instrument with which Edwin Hubble discovered (or proved, depending on whom you talk to) that the universe was expanding.

Photograph by Leor Levine

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More About

• Edwin Hubble
• Mount Wilson
• Don Nicholson
• Sciences
• Science and Technology

I moved to Pasadena in 1981 when my father took a job at the Jet Propulsion Laboratory, and Mount Wilson has been with me ever since. It’s the tallest summit in our little stretch of Sierra Madres, and you can see it from the entire city. Since I was 14, it’s been framed right in the center of my bedroom window (I’m looking at it right now). My father is a physicist - to the aging crack about smarts that went, “What are you, some kind of rocket scientist?” he always responded, “Yes indeed!” - and he gave my brother and me an early start with the sciences. Next to our charts of the solar system, we had mural-sized posters of eclipses, Io’s angry volcanoes and Europa’s mottled tundra, with its zigzagging furrows. I was up on quasars, brown dwarves, pulsars, the date of Voyager II’s expected Saturn flyby. And I knew that Hubble made one of the most important cosmological discoveries, one that fundamentally changed our idea of the universe - even Einstein’s idea of the universe - right up there on Mount Wilson. There’s a canyon below the mountain, and right at the edge, hidden by a barricade of oleander, is a little platform where I liked to take girls in high school, not only because it was secluded but also because we could talk about the string of lights up on the mountain and how they gave us the universe that we know. Those lights blinked slowly over my first kiss.

Despite all this, I had never been to Mount Wilson until recently. Like most people, I assumed that the observatory no longer operated — that light pollution had rendered the telescopes ineffective decades ago. I am admonished about this on my first visit by Don Nicholson, the associate director of the Mount Wilson Institute, who explains that the Hooker and the other telescopes have been in daily use since they were built (except for an eight-year stretch when the Hooker was offline for lack of funding). A full staff continues to use the daylight to watch the sun; and the night sky, which filters through some of the world’s calmest air, affords what astronomers call good “seeing” - down to half an arc-second on some nights, a resolution that, as the convivial octogenarian Nicholson says, “makes other astronomers drool.” And lately, Mount Wilson has been home to some pioneering technologies that make the observatory as relevant as ever. Despite the smog and the encroaching city, Los Angeles still gives us a great sky.

The Mount Wilson grounds occupy about 40 forested acres atop a 5,700-foot peak that overlooks much of Southern California, from Mount San Jacinto to the Malibu hills. Its spot on the ridge is tight, almost precarious. From some points the crest becomes so narrow you’ll look south and find Catalina floating in the mist and then turn around to see the Angeles National Forest stretching off toward the Mojave Desert. From these places, the view due east is divided equally between a solid urban grid and empty wilderness.

The solar observatories on Mount Wilson are imposing towers, although the giant structures we see from the city are the nearby broadcast facilities. Together, the various spires and domes feel sci-fi: They give the impression, especially at night, of some kind of far-off research colony. People do live there, and for them there is a cluster of buildings that provides housing, a galley for cooking, and a library.

Dwarfing them all is the dome of the Hooker 100-inch telescope, which is settled on a north-facing, downward-sloping promontory that puts it out of sight of city lights. It looks like what we imagine observatories to be because it set the standard: a massive white metal cap, raised on a pedestal, with a wide arc of a door that opens to reveal the cage and optics that make the heavens visible.

The Hooker was finished in 1917, after three years of construction, and it’s built like a dreadnought - solid steel top to bottom, a massive complex of structure, supports and bulkhead doors. “They didn’t have finite element analysis back then,” Nicholson says as we enter the open floor of the observatory. “So they overengineered. They just worked it out on the back of an envelope and doubled the numbers.” The telescope weighs 50 tons and the dome twice that, and both are moving parts: While the scope swivels, the full range of the sky is reached by turning the entire dome. The reflecting element at the bottom of the scope is 9,000 pounds of wine-bottle glass from the Saint Gobain bottle works in France. It remains the largest solid plate mirror ever cast. All of this was hauled up the tortuous Mount Wilson Toll Road by burro and a few specially designed Mack trucks, which, as you’d expect of trucks built in 1917, often got stuck and required assistance from the donkeys and their drivers.