At the top of Mount Hamilton, near San Jose, Calif., Lick Observatory looks out over the dense sprawl of the San Francisco Bay Area. On a clear day from the 4,200-foot summit, you can see San Francisco to the north, as well as the entrance to Yosemite Valley, 120 miles east, as the crow flies. At night you can see even farther — millions of light-years into space.
When it was completed in 1888, Lick (named for its sponsor, James Lick) boasted the best telescopes and best year-round conditions of any observatory in the world. Its white domes were beacons for astronomers and visiting dignitaries, as well as hundreds of curious locals who made the long journey up the mountain each weekend.
Now, Lick Observatory is one of only a few remaining historic observatories still open to the public in the United States. Contemporary funding prioritizes ever-larger telescopes in dark, dry, high-altitude sites, like Chile’s Atacama Desert, or space-borne telescopes, such as the Hubble Space Telescope or the James Webb Space Telescope. Theirs are the extraordinary discoveries that regularly make the news. But historic observatories still have wonders to share with visitors and astronomers alike.
Lick Observatory and Lowell Observatory in Flagstaff, Ariz., which opened in 1894, both remain active in astronomical research. Other historic observatories now focus primarily on public outreach and education, including Yerkes Observatory (1897) in Williams Bay, Wis., and Mount Wilson Observatory (1904), outside Pasadena, Calif. At each of these sites, you can step into the history of the cosmos — experiencing the deep time of the stars, as well as more recent histories of discovery.
Looking through 19th-century glass at the Lick, you can see where E. E. Barnard spotted a new moon of Jupiter and James Keeler found a gap in Saturn’s rings. At Mount Wilson, Edwin Hubble, building on work done by Henrietta Swan Leavitt at Harvard, made an observation that proved there were other galaxies in the universe beyond the Milky Way. At Yerkes, you can peer through the 40-inch refracting telescope that surpassed Lick’s in size in 1897 and was used by a cadre of path-breaking women working in astronomy.
As the artist Aspen Mays and I prepared to visit Mount Hamilton this fall, she reminded me of yet another layer of time we would be traversing on our trek up the mountain: the white domes that now stand as accidental monuments to anthropogenic change. In the valley below the Lick, most people can barely see the stars at night because of light pollution. Although the skies above Lick were exceedingly dark through the 1940s, postwar growth led the observatory to start researching new locations in the mid-1960s. As the astronomer Merle Walker explained when the results were published in 1970: “The quality of the observing conditions at Mount Hamilton has begun to deteriorate due to the increase in lights and smog.”
The metropolitan-adjacent locations of Mount Hamilton and other historic observatories now seem acutely incongruous. With sky glow clearly visible from these once-dark sites, they are potent reminders of just how much has changed since their construction. But visiting them now can also inspire us to reverse those changes, both at the historic sites and in the places where we live.
The narrow, winding road to the Mount Hamilton summit is scrawled through golden hills and overhung by oaks. Halfway up the mountain, the fog-like marine layer pulls away in tatters, revealing steep cliffs on the outside edge of the road and piles of dusty rock in the tight turns. The smell of pine and the calls of acorn woodpeckers emerge with the sunlight, and a passel of wild boar pick their way through the grasses, the small ones nibbling as they go. For a few miles, the observatory is hidden by the sharp ascent of the mountain.
In Lick Observatory’s Historical Collections, images of astronomical objects are interspersed with scenes of daily life on the mountain. You may find a snapshot of fog swirling in the valley filed next to a photograph of the moon’s Sea of Tranquility, or a convivial picnic followed by a comet barreling through the black sky. Some of these astronomical photographs would redefine what we know of Earth’s place in the vast universe.
Yet, as the staff astronomer Elinor Gates told me, nothing compares to seeing these objects through the eyepiece of a telescope on the mountain. “You might look at a galaxy and it’s 25 million light-years away,” she said with visible enthusiasm. “It’s taken 25 million years for that light to get from that galaxy, come through the telescope to the eyepiece, to your eyeball. It’s a different experience than just looking at a pretty picture on a computer screen or in a book.” Here, she said, “You can actually start to experience the depth of time.”
Standing at the base of the Great Lick Refractor, I am stunned by its scale. Its tube reaches 57 feet toward the steep pitch of the dome, a 99-ton galvanized steel behemoth capable of rotating 360 degrees to accommodate the telescope’s opening. The walls are paneled with fragrant local redwood. Even the floor is exceptional — not only for its elegant circular parquet, but because the whole thing is an elevator, which once lifted astronomers up to the level of the eyepiece no matter where the telescope was pointed. And all of this material bounced and creaked up the mountain behind mules more than a century ago.
John Barentine, an astronomer and consultant focused on dark skies research and conservation, believes that looking through a telescope can be transformative. “If I show somebody the moon through a telescope, they can, for the first time, envision it as a place,” he told me. “Now they’ve had a kind of direct experience with it.” But those rewards, he cautioned, are dependent on if and how we rein in light pollution on the ground.
There is a growing collection of scientific literature documenting the harmful effects of light pollution, which impacts far more than astronomical observation. Humans evolved under the sky. Our biology remains connected to its rhythms of darkness and light. Myriad other species also rely on the natural night sky for everything from navigation to hunting, growth and reproduction. In his book, “The Darkness Manifesto,” the zoologist Johan Eklöf describes in detail the negative effects of excess artificial light on plants and animals, including birds, bats, sea turtles and corals. Dr. Eklöf notes that half of the world’s insects are nocturnal; they are easily led astray by artificial lights at night, which create a “vacuum cleaner effect.” On a large scale, this can draw insects from more rural areas to brightly lit cities and lead to changes in the entire ecosystem.
Despite our awareness of its harm, light pollution is advancing at an alarming rate. A groundbreaking 2016 study, which used satellite data to evaluate artificial night sky brightness globally, determined that 80 percent of the world’s population lived under light-polluted skies. In a more recent study, data collected by citizen scientists have been used to determine that on average the night sky brightened by 9.6 percent per year between 2011 and 2022. In observable terms, the study’s authors explain, this means that if you could count 250 stars outside tonight, in just 18 years you’d see only 100 in the same location.
Dr. Barentine told me that the technical solutions for fighting light pollution are known and proven. “All we are missing,” he said, “is the will to put those in place.” These include implementing local lighting ordinances that limit outdoor lighting to where and when it is useful, and regulating the colors of outdoor lighting to longer wavelengths, like amber, so that scattering is less pervasive.
Flagstaff, home of Lowell Observatory, has been protecting the dark sky as a natural resource for more than half a century. Jeffrey Hall, Lowell’s executive director, told me that you can still see the Milky Way from downtown. The city’s first lighting ordinance, passed in 1958, prohibited the use of advertising searchlights. By the late 1980s, the ordinance was strengthened to require shielded outdoor lights that direct illumination downward, as well as “spectrum management,” which limits approved lighting to certain wavelengths.
Dr. Barentine suggested that light pollution is “the environmental challenge that we could definitively solve in our lifetimes.” And our success, he said, could benefit far more than just the field of astronomy. “We need a win as a species,” he said. “We need people to believe that we can take on significant problems and solve them.”
Those significant problems are all around us today. The charred skeletons of oak and manzanita sketch a haunting ring around Lick Observatory. In August of 2020, lightning ignited the drought-stricken hillsides. Residents were evacuated and several structures were lost, but fire crews managed to save the historic domes and equipment. When Aspen Mays and I visited this fall, smoke from wildfires burning along the California-Oregon border had drifted hundreds of miles south, drawing an acrid scrim over the Bay Area. As Aspen pointed out, when these observatories were built, their founders compiled years of meteorological research to confirm the sites’ future viability. No one expected the very climate to change.
At historic observatories we can see the enormous gains we’ve made in understanding our place in the universe, but they can also show us what we’ve lost — and what we will continue losing if we don’t do more now to limit our impact on the planet and the sky above it.
If you go …
Lick Observatory, in Mount Hamilton, Calif., is usually open year-round. Weekend activities at the site include exhibits in the main observatory building, free timed talks in the dome of the 36-inch Great Refractor and a gift shop. The visitor’s gallery of the Shane 120-inch reflector telescope is open daily. View the observatory on Google Maps.
Lowell Observatory, in Flagstaff, Ariz., is open year-round. Ticketed activities on offer include stargazing, exhibits and science demos, scheduled science talks and opportunities to meet working astronomers. View the observatory on Google Maps.
Mount Wilson Observatory, outside Pasadena, Calif., has daily hours. The observatory and grounds are open to the public; during spring and summer, public programs include lectures and concerts, as well as opportunities to observe through the historic telescopes. View the observatory on Google Maps.
Yerkes Observatory, in Williams Bay, Wis., is situated on elegant grounds designed by Frederick Law Olmsted, which are open to visitors year-round. Tours and programs at the Observatory feature architectural and astronomical history, as well as music performances and talks on science, contemporary art and literature inspired by the cosmos. Events and tours are ticketed, so be sure to book in advance. View the observatory on Google Maps.
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