The Perfect Machine (75 page)

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 star.

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.

Baade then brought William Baum, an expert in photometry, up to Palomar to measure the light-gathering and resolving power of the
telescope by setting up photometric sequences. Baum’s tests agreed with the earlier calibrations. The telescope
could
detect magnitude 22.4 stars in a thirty-minute exposure. Separately, from a study by one of his doctoral students, Baade confirmed the absolute magnitude of
RR Lyrae
stars. That Baade couldn’t detect these stars in the central region of Andromeda, after a careful survey, confirmed his division of the variables into two distinct populations. In Rome at the 1952 meeting of the International Astronomical Union, Baade announced his findings. Shapley’s light curves for variable stars were too simple. By identifying two distinct populations of variable stars, Baade had corrected Hubble’s scale, doubling the size of the universe. The first major discovery of the two-hundred-inch telescope was from what it couldn’t see. Imagine, astronomers said to themselves, what the telescope will discover from what it can see.

Astronomy is an incremental science. Although reporters puff each report from a meeting of the AAS or the IAU into what sounds like a definitive proof of the big bang, black holes, or dark matter—a night, or even an entire observing run on a telescope, rarely produces a revolutionary discovery. Each night adds data, fragmentary glimpses and measurements of the reaches of universe that astrophysicists and cosmologists can use to build, modify, or undermine features of a constantly evolving model.

Yet amidst that steady accumulation of knowledge, the achievements of the two-hundred-inch telescope stand out as a history of twentieth-century astronomy. It was on the two-hundred that Baade’s student Allan Sandage pursued his long search to refine the Hubble constant, the magic number that would define the age and size of the universe. It was on the two-hundred that Baade and others went beyond the geometry of space that Hubble had explored to identify distinct populations of stars and to explain the evolution of stars, the processes at work as stars were born and died. As the geometry and astrophysics came together, mostly from research done on the two-hundred-inch telescope, it became possible to age-date stars, to begin to understand the mysterious processes at work in the galaxies, and to discover large-scale structures in the universe.

With new instruments, tiny Schmidt cameras that Don Hendrix built with sapphire or diamond lenses, more sensitive photographic emulsions, phototubes and photomultipliers that could record light too faint for a photographic emulsion, corrective lenses with even broader fields than the Ross lens, finer spectrographic gratings, and tricky observational techniques that pushed the equipment to the limits—the reach of the telescope extended further than even the wildest optimists had dared to predict.

After Baade retired back to Germany, in 1958, Rudolph Minkowski took over some of the research Baade had pursued. Minkowski, a big
hulk of an astronomer, was famed for ineptness around machines that seemed the perfect inverse of Baade’s skill. Night assistants who drifted over to the two-hundred knew two sure ways to tell when Minkowski was on the telescope: the aroma of the smokey Lapsang souchong tea he brought to the dome with him, and the sounds—many not suitable for polite company—that came over the intercom from the prime-focus cage as Minkowski’s body protested at the cramped quarters. Baade claimed that the hayrake seat in the prime focus, too big for his diminutive frame, had been shaped from a plaster cast of Minkowski’s derriere.

Minkowski was persistent, and he got results. On his last run on the two-hundred-inch telescope, in the spring of 1960, he was determined to get a spectrum from an elusive and suspicious object, identified from the Cambridge compilation of radio sources as 3C 295. The object was so faint he couldn’t see it to center it on the slit of the spectrograph. He would have to guide the telescope, for a whole night of exposure, on a dark area of sky where previous direct photographs had identified the object. His final run on the telescope was scheduled for four nights. The first two nights were too cloudy to observe. Minkowski moped around the Monastery, watching his chances slip away. The next night the weather cleared, and he held a faint guide star in the crosshairs of his guiding eyepiece for an entire night. He and Allan Sandage had previously taken “trial plates” to determine that the tiny area of blackness that hid 3C 295 would be on the slit of the spectrograph if the guide star was in the crosshairs. Minkowski gambled, and on the fourth night continued the exposure—trusting Sinclair Smith’s wonderful control system to keep the telescope pointing to exactly the same spot. At midnight on the last night he rushed the slide down to the darkroom and developed it. The red shift he measured for 3C 295 was .46, meaning that the strange object was receding at 46 percent of the speed of light. It was the most distant and fastest-moving object yet discovered. Minkowski bounded into the Palomar library with a bottle of bourbon and three glasses, for himself, Sandage, and night assistant Robert Seares. Despite Byron Hill’s rules, he was going to celebrate. The “look back time” to 3C 295 was somewhere between one-third and one-half the age of the universe.

Not every experiment was a success. There were some legendary failures. Fritz Zwicky was allocated little time on the two-hundred-inch telescope. In one experiment he used the two-hundred-inch telescope and the “little” Schmidt telescope, a few hundred yards away, to study the effect of artificial meteors on the atmosphere. The experiment required Ben Traxler, Zwicky’s favorite night assistant, to stand in the open shutter of the telescope, firing his .30-.30 carbine into the air while both the two-hundred-inch and Schmidt telescopes tried to record the path of the bullet. When the report from the rifle echoed over the mountaintop, astronomers accused Zwicky of trying to punch
a hole in the atmosphere to improve the seeing. Experiments like that one weren’t repeated.

Hubble suffered a heart attack in 1949 and was ill by the time the telescope was ready. In a photograph taken in the prime focus, he looks wan and pale. A bell was rigged near his bed in the Monastery, and the night assistants went out of their way to accommodate him on his few observing runs. When he could no longer observe, he picked a surrogate observer to carry on his work, Allan Sandage. As an undergraduate at the University of Illinois, Sandage had read about the telescope in David Woodbury’s book and decided that he would go to California to study with Hubble, the most famous astronomer in the world, and somehow work on the most famous telescope in the world. As one of the first Ph.D. students in astrophysics at Caltech, Sandage learned from Walter Baade the skill of identifying a Cepheid star among the thousands of stars in an image of a distant galaxy and then using the remarkable abilities of a trained human eye to compare the brightness of the Cepheid with other stars so its light curve could be calibrated. Allan Sandage probably spent more hours of dark time on the two-hundred than any other observer during its early years, as he relentlessly pursued the goal of refining the Hubble constant that relates the red shifts of distant galaxies to their distance, and thus gives the size and age of the universe.