The Perfect Machine (74 page)

Hendrix started with a twelve-inch polishing tool on his machine and gradually worked his way down to tools the size of a half-dollar. As the edge was brought down, Bowen and Hendrix began to identify small zones of the mirror that needed correction. The zones were too
small to use the polishing machine, so Hendrix and Johnson would use handheld cork tools to remove five- or six-millionths of an inch of material. The observatory wasn’t a “clean room” like the optics lab, but for the sake of the opticians’ concentration and cleanliness, no one else was allowed on the observatory floor while Hendrix and Johnson worked.

Sometimes the weather or the seeing wasn’t good enough for testing the mirror, and everyone would have to wait for days for another round of tests. When the remaining defects were too small for the cork tools, Hendrix and Johnson would polish the mirror with their thumbs. They would dip a watercolor brush in a slurry of water and polishing compound—a mixture called Barnesite—paint the zone with the brush, then polish with a few strokes of a naked thumb. The thumb was a good instrument; it didn’t slip. Each stroke would remove one- or two-millionths of an inch of glass. After a few strokes, sometimes only one or two, they had to stop, because the heat of their thumbs and the pressure of the polishing would have heated and expanded the mirror. The whole polishing that day might have taken two or three minutes. The disk then had to be remounted on the telescope, an operation that took most of a day. The crews got practiced at removing and re-attaching fourteen and a half tons of mirror and mirror cell.

The final figuring of a telescope mirror is a battle between perfection and reality. The opticians begin talking fractions of a wavelength of light, distances that have little meaning when they are translated into inches or even millimeters. The opticians’ eyes glisten as they dream of achieving what no other optical surface has achieved, a surface so smooth that if the two-hundred-inch mirror were the size of the continental United States, it would have no bumps on its surface higher than a few inches.

Several times a week Bowen would give the lunch group at his favorite sandwich shop his latest report on the status of the mirror. The astronomers were champing at the bit: There are never enough big telescopes, never enough hours of observation time. While the opticians polished, the research projects—especially projects that could
only
be completed on the two-hundred-inch telescope—piled up. The astronomers wanted,
needed,
the telescope. Atmospheric effects and defects in the photographic emulsions, they argued, would mask any further improvements in the mirror.

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 dusk 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.