The working astronomers and astrophysicists weren’t the only ones waiting impatiently for the telescope. News stories about the telescope had inspired a generation of aspiring scientists. Graduate students in astronomy came to Caltech, with its fledgling astrophysics department, in the hope of working on the biggest telescope in the world. Steven Weinberg, now a Nobel laureate in physics at the University of Texas, was in high school when he read that the “big telescope at Mt. Palomar was going to start operating soon…. I thought that as soon as they went from a 100-inch to a 200-inch telescope, then suddenly all the problems would be solved, and that would be really exciting. We would know whether the universe expands forever or collapses.”
Across the top of the mountain, the forty-eight-inch Schmidt telescope was already in operation. Hendrix had taken the first official photograph, of M31 (Andromeda), on September 24, 1948. The quality was good enough for the plate to later be included in Hubble’s Atlas of Galaxies. On the night of July 19, 1949, Albert Wilson and Robert Harrington exposed the first two plates of a sky survey, sponsored by the National Geographic Society and Palomar Observatory and designed to photograph the entire observable sky from Palomar with both red-and blue-sensitive plates. The Schmidt camera would record stars and galaxies of even fainter magnitudes than those Hubble had urged when he thought the Schmidt telescope was for his own proposed program of galaxy counts, a research program that had been slighted in the observation plans for the two-hundred-inch telescope.
The survey was exacting. The emulsions from Eastman Kodak, on thin fourteen-inch square glass plates, had to be bent in the darkroom on a curved mandrel; many broke in the test. Each plate would take in a six-degree square chunk of the heavens. To get the focus right each night, the observer had first to expose a test plate with different focus settings, rush it downstairs to the darkroom by dumbwaiter, then examine the images under a microscope to determine the exact focus for the next plate. Eight or ten exposures would constitute a night’s work. An airplane flying overhead during an exposure would ruin the plate. The plates were developed immediately; the microscopic examination of each plate for previously undiscovered asteroids, comets, and supernovas, might take weeks. Fritz Zwicky was accused of rushing over to the big Schmidt dome early in the morning to check the plates from the night before so he could be the first to follow up on any discoveries. The complete survey would take years. Collections of copies of the plates or printed photographic editions of the Palomar Sky Survey became a basic research tool for astronomers everywhere.
By the fall of 1949, Bowen’s test results on the two-hundred-inch mirror were getting better. The Mount Wilson and Caltech astronomers had studied enough optics to read the test photographs, and they began to protest the prolonged final figuring. Hendrix and Johnson told Bowen they needed one more week with their thumbs and the Barnesite. When that was over, they wanted one more, and then another after that—a few more chances to reach perfection. Bowen was a physicist by training, closer to the astronomers than to the opticians, but he had been entrusted with a unique challenge. Like so many other men before him, he was caught up in the spell of the original grant language—to build a telescope “as perfect as possible.”
He sided with Hendrix and Johnson. There was only one two-hundred-inch telescope. Bowen wasn’t going to let it go until it was ready.
He kept testing. The design of the mirror cell allowed air to circulate freely around the outer edge of the mirror. After a substantial temperature change in the observatory, he discovered, the edge cooled quicker than the rest of the mirror, distorting the surface. Bowen had fans installed in the cell to circulate the air inside, and added aluminum foil insulation enclosed in heavy craft paper. Running the fans for an hour or two when there had been a major change in the temperature seemed to solve the problem.
By the end of September, Hendrix and Johnson were down to single-stroke polishing, a bare touch of the thumb with Barnesite and water. The additional figuring of the mirror had taken five months. Less than seven hours of that time had been spent actually polishing. The rest of the time was testing, removing, and reinstalling the mirror; reduction of the test results; and the long intervals between strokes of the opticians’ thumbs. Hendrix and Johnson would have been content to continue another two years, but Bowen, under increasing pressure from the astronomers eager to use the telescope, began talking of “final” tests. The zonal problems had disappeared, and in most orientations of the telescope, the tests with the Hartman screen were almost perfect. The one remaining problem was a trace of astigmatism in certain elevations of the telescope. Hendrix estimated that it could take months to polish out the astigmatism and that polishing might not work, because the problem could be in the support mechanisms.
No one had the stomach for another round of rebuilding the support systems. Bowen calculated the forces needed to correct the astigmatism. It came out a few ounces of pull at selected points on the back of the disk. As an experiment he purchased four cheap fisherman’s scales at a hardware store. When he got behind the mirror, he hesitated; his calculations had been exact, but he temporarily forgot whether he wanted to push or pull the mirror. Ben Traxler, watching, chided him: “Was it a plus sign or a minus?” Finally Bowen hooked the scales onto the weights of the axial supports at the quadrants of the mirror, northwest, southwest, northeast, and southeast. On the next set of tests the astigmatism disappeared. Bowen left the scales in place.
In October 1949 he told Hendrix to put a new coating of aluminum on the mirror. It was time to turn the telescope over to the astronomers.
35
Palomar Nights
The old road from Pasadena to Palomar ran past the campus of Pomona College in Claremont, through tree-shaded villages, orange groves, clusters of palm trees, and irrigated valleys, before reaching the desert mountain. The Pasadena astronomers had a running challenge for the fastest time for the 134 miles to the observatory; Jesse Greenstein, a master of back roads, claimed the record. The races didn’t end until freeways and spreading development replaced the old California of orange groves and palms.
Today, only the climb to the peak from the bottom of the mountain is unchanged from the days when huge tractor-trailers hauled sections of the mounting and the great mirror up the mountain. The road traverses a rainbow spectrum, from the desert oranges and browns of the Native American villages at the base of the mountain, with their ramshackle fences, wandering cattle, and the tired machinery of hard-scrabble farming; to the fine greens and tans and splashy wildflowers of the high meadows; and still higher, the dense, dark green of the evergreen forest.
The first glimpse of a telescope dome, from a curve in the road, is a surprise. The domes were originally painted with silver aluminum paint. Today they are covered with a brilliant magnesium paint that reflects the sun’s heat, in an effort to improve the local seeing and the temperature stability of the optics. The dazzling white, glistening in the distance, is like a glimpse of the domes of Jerusalem by a pilgrim. Even for an astronomer jaded by hundreds of nights on big telescopes, that first sight is electrifying.
There’s a long way to go from that first glimpse to the top of Palomar Mountain. The peak is a shallow glen between two long north-south ridges. Outcroppings of granite stand proud in the scrub brush, meadows, and big-cone spruce forest. On a good day the Pacific Ocean is a smear of blue to the southwest, thirty-five miles away.
There are almost always visitors in the daytime. The weekend of Labor Day 1948, when the telescope was still in trials, three thousand tourists showed up. There’s a small museum, with a mockup of the structure of the mirror and exhibits explaining and illustrating the work of the two-hundred-inch. From the museum a pathway leads to the main entrance of the two-hundred-inch dome, which opens into a glass-enclosed visitors’ gallery. The old concrete dummy mirror is along the walk, just past the dome, but few notice it. In the afternoon tourists watch the astronomers and technicians readying instruments on the telescope. By dus
k the gates are closed and the tourists go home. The mountain then belongs to the astronomers.
Observing time on the two-hundred-inch telescope is one of the world’s rare commodities. The Allocation Committee, successor to the small group of astronomers and physicists who met at Hale’s solar laboratory after the war to decide who would use the telescope, reviews a constant stream of applications. The guiding policy for the two-hundred-inch telescope has been to favor projects which could only be undertaken on the large telescope, and which promise a good chance of success. The tea leaves of their decisions are scrutinized with endless care. Some research topics and directions are fashionable. Some observers have a talent for pursuing the hot issues. With time on large telescopes severely limited, there is a bias toward positive results. A few observers get a lion’s share of the valuable “dark time,” when the moon is not up.
Time on big telescopes is too valuable to waste. Before World War II, Walter Adams kept the big telescopes at Mount Wilson operating every night of the year that weather permitted, including Christmas Eve, Christmas, and New Year’s Eve. It was only during the war that he agreed that there would be no observing on Christmas Eve or Christmas Night, so the night assistants could be with their families. Observing is scheduled for every night of the year at Palomar except the occasional “engineering runs” that are reserved for maintenance work on the telescope, such as the periodic washing and realuminizing of the mirror or the installation of new instruments.
Like much of science astronomy today often calls for collective efforts. Teams of two or more astronomers and astrophysicists will work together on an observing run, sometimes joined by physicists, radio astronomers, computer experts, spectroscopists, and others. A shuttle several times a week brings astronomers, technicians, and graduate students from Pasadena to Palomar. Observers arrive from institutions across the country or across the world. The rental cars from San Diego, Los Angeles, or Orange County Airports appear in the afternoon, in time for a night of work. Chronic jetlag, aggravated by long nights and the shift from day-to night work, is an occupational hazard of astronomy.
Supper in the Monastery is served before dark. There is a tradition of good, hearty food at the observatory—energy and warmth for the long nights—even though winter suppers can end up at an uncivilized hour to accommodate observers who want an early start. Observers with spare moments relax in the Monastery lounge, where the bookshelves are filled with mysteries, old issues of the yearbooks of Mount Wilson and Palomar Observatories, and recent scientific journals. Caltech is a school with a long tradition of practical jokes, and the joking sometimes extends to the observatory, where journal articles or books by rival astronomers will mysteriously appear open on tables in the Monastery.
Pool on cloudy nights is another longtime tradition. At Mount Wilson skill at pool was valued almost as highly as the famed observational skills of Walter Baade and Milton Humason. The favorite game was “cowboy,” and the Saturday-morning games between John Anderson and Frank Ross, at the Santa Barbara Street labs, drew heavy betting. When Palomar opened for regular use, Olin Wilson asked for a pool table on the mountain. Ike Bowen reluctantly authorized the purchase of a used table, as long as it cost less than one hundred dollars. A collection from astronomers and staff bought cues and balls, and Wilson got one of the night assistants to help him recover the table with new felt.
Palomar is no longer the isolated peak Hussey surveyed in 1903. At dusk darkness comes suddenly to the mountain, but today the overhead canopy of stars is dimmed by the looms of light of Los Angeles to the northwest and San Diego to the southwest. The light pollution would bring chills to George Hale, who thought this remote mountain safe forever. San Diego years ago agreed to use low-pressure sodium illumination for outdoor public lighting; the distinct yellow light can be filtered from images and spectra. In 1993, supposedly as a crime-prevention measure, the San Diego City Council reversed the decision and authorized the use of high-pressure sodium lights. The light from Los Angeles is unbridled and has steadily diminished the effectiveness of the telescopes even as far away as Palomar.
But even with the troublesome light pollution of the distant cities, the heavens from Palomar are magic. No exterior lights burn at the observatory, so eyes can adjust quickly to the night sky. On a night with good seeing, the canopy overhead is ablaze with pinpoints of light. Familiar constellations are sometimes hard to find in the blanket of stars. The Milky Way can be so dense it is difficult to discern individual stars. The seeing at Palomar has never matched the best of the seeing at Mount Wilson, but the observatory has made a long effort to reduce locally generated atmospheric turbulence with new paint on the domes, insulation of the dome floor, and by removing or insulating internal sources of heat in offices, electrical equipment, oil tanks, pumps, and motors. Astronomers rate the seeing each night in arc seconds of resolution, the lower the better. The seeing the night before—on a good night it is below an arc second—is a sure subject of discussion at breakfast in the Monastery.
The shutters of the big dome are usually opened in late afternoon, to allow the telescope to adjust to the outside temperature. In early tests the dome insulation held the interior temperature to within 0.1° over twenty-four hours, but every night is different, and every procedure that can improve the local seeing helps. The open shutters on the dome at dusk are a beckoning invitation as the astronomers drive or walk from the Monastery to the telescope.
The walk is best. From a distance it is easy to mistake the dome of the two-hundred-inch telescope for the full moon rising over the crest of the mountains. The dome stands proud on a meadow, elegant in its simplicity, anchored by the simple banded base of Russell Porter’s design. There are no frills. It is big enough to enclose a twelve-story building, but the proportions are visually comfortable. Even with a glimpse of the telescope visible through the shutter, it is hard to believe that the building is the housing for a scientific instrument and not a temple or monument.
Astronomers enter not through the porticoed entrance used by tourists, but at a simpler door into the lower level. The ground floor is a cluttered industrial workshop—tables and cabinets of tools, fork lifts, tanks of liquid nitrogen to cool electronic devices, barrels of Flying Horse Telescope Oil for the pressure bearings (when Mobil announced that they were discontinuing the product in favor of a synthetic oil, Palomar cached a big supply). The footings of the telescope stand out amidst the tanks and equipment—massive, simple girders, rising from four points. The joints are welded and bolted, a belt-and-suspenders precaution. The footings were later modified to add a safety brace, lest the telescope literally jump off its footings in an earthquake, but as the geologists predicted, the granite mountain has been spared major earthquakes. Around the edges of the lower level are storerooms and former darkrooms that have been converted for storage. Up a flight of steel stairs is the main floor of the observatory.
Even astronomers who have worked at other big telescopes are awed by the two-hundred. The arch of the huge interior space seems immense yet pleasing. The final dome dimensions—the width is equal to the height—were chosen to match the f-ratio of the telescope, but the balanced proportions recall the harmonious architectural magic of spaces designed for their effect, like the interior of Saint Paul’s in London or the Pantheon in Rome. In the dim light of early evening, with a slice of the sky in the open shutters of the dome, the building feels like a cathedral.
Everyone has seen photographs of the two-hundred-inch telescope, but the scale of the machine, the sheer size of the massive horseshoe and the side tubes that lead down from the horseshoe to form the yoke, is more than the photographs convey, even the photographs that show tiny human figures next to the telescope. The apparent simplicity is striking. There are no frills, not a single ornament. The gray mounting is stark and smooth, without rivets or seams. It seems impossible that this huge machine, weighing twice as much as the Statue of Liberty, could move with the incredible precision to point at a s
tar.
Observing on the two-hundred-inch telescope is a humbling experience. The machine carries a history, the legacy of achievement. This was the instrument that led the great twentieth-century voyage into cosmology.
It began when Walter Baade used the two-hundred-inch telescope to double the size of the universe.
As soon as the telescope was ready for astronomers, Baade turned it toward his favorite target, the Andromeda galaxy, hoping to end a long-standing dispute. Hubble had used Shapley’s calibration of the period-luminosity relation for Cepheid variables to fix the distance of Andromeda at 750,000 light-years. If his distance scale was correct, the (RR Lyrae) variable stars of period less than one day in the central region of Andromeda should have had a photographic magnitude of 22, well within the range of the two-hundred-inch telescope with a thirty-minute exposure. In one of his few kind words for the two-hundred-inch telescope, Shapley predicted that it would resolve the RR Lyrae stars in Andromeda and thus give a final validation to positions he had held since the great debate of 1921. Baade, who had studied Andromeda for years, including his miraculous wartime resolution of stars in the nucleus with the Mount Wilson telescope, was convinced that simple extrapolation of the light scales of Cepheid variables was wrong, because it failed to distinguish between two different populations of stars. The test was whether the RR Lyrae variables in Andromeda could be detected at the predicted magnitude.
Baade was a master of the new machine as he had been of the old. His reputation as an observer was so formidable that other astronomers claimed that Bruce Rule would give the mirror supports of the telescope a special tuneup before Baade had a run on the telescope. In his earliest runs Baade turned the telescope toward Andromeda. “The very first exposures on M 31 taken with the 200-inch telescope,” Baade recalled, “showed at once that something was wrong.” Earlier tests had showed that the two-hundred-inch telescope would detect stars with a photographic magnitude of 22.4 in a thirty-minute exposure, but as he predicted, Baade could not detect the variables. Shapley responded with a last lick at the new telescope: Maybe, he said, the telescope wasn’t good enough to detect the stars.
The Perfect Machine Page 57
