The Perfect Machine (76 page)

Sandage used the two-hundred to show that the most distant “stars” Baade had observed were actually H II (ionized hydrogen) clouds. That finding again doubled the scale of the universe. Later, on plates taken with the two-hundred-inch telescope, Sandage discovered a new class of stellar object. He called them “quasi-stellar radio sources,” a name that was later shortened to “quasars.” For a long time no one could explain these strange objects, until Maarten Schmidt, using spectra taken on the two-hundred, concluded that the light from the quasars was shifted so far toward the red end of the spectrum that they had to be moving at inconceivable speeds. Quasars were the most distant and most luminous objects ever recorded. The telescope, it seemed, was reaching to the very edge of the universe.

The race to find objects with ever greater red shifts was on. Reporters clamored for more exciting reports, and the Caltech publicity office was ever ready to satisfy the requests with a new breakthrough. “Those are the days when you’d come down from Palomar,” Sandage recalled, “and everyone would expect you to come down with a pot of gold. Sometimes, almost always, it worked: new quasars, the biggest red shift, variability, are they galaxies or are they nearby?” The two-hundred had gone beyond even the most optimistic of hopes.

Even when larger telescopes came along, and when research on radio telescopes, neutrino detectors, and satellite-borne instruments compete for space in the journals and headlines in the science sections,
those heady days of reaching for the edge anointed the two-hundred-inch telescope as the machine that opened the universe.

Astronomers usually show up at the dome around dusk. When the telescope first went into service, observers came down early to sensitize photographic plates in special hypering solutions. For some observation programs the astronomer would have to work in absolute darkness to cut the glass emulsions into small squares and bake them in an atmosphere of dry nitrogen to increase their sensitivity. An invisible speck of dust in the wrong place on the emulsion would ruin a night’s work. Before the run began, the observer would give the night assistant a handwritten or perhaps typed list of objects with their coordinates. The observing positions in the prime-focus cage and the swinging seat on the Cassegrain focus were connected by intercom to the night assistant’s console, but the astronomer, once loaded into his seat, was alone for hours. For the prime focus the observer would ride a small open elevator up the inside of the shutter opening. The elevator would stop at the level of the prime focus, and the observer would step out, across a ten-inch gap, into the cage.

Once, when the prime-focus elevator broke before a scheduled observing run, the night assistant loaded a young, willing Allan Sandage into the cage by lowering the tube to its lower limit and letting Sandage climb up on a rickety ladder, like a carnival stunt man loading himself into the muzzle of a cannon. As the telescope slewed up, he was a prisoner in the cage. For cold winter nights the observers wore war-surplus electrically heated flight suits. For hours they would sit, cramped in a small tube, in subzero temperatures, without light, food, drink, or access to the toilet. As the suits wore out, sometimes the heating wires would chafe and be exposed. Bladder control in an electrical “hot” suit was at a new premium.

Yet for all the rigors of a cold night in a cramped cage, observing at the prime focus is a magical experience. The observer can glance over the edge of the cage, or down from the prime-focus elevator, and see directly into the mirror. The achievement of seventeen years of work—the masterpiece that McCauley, Brown, Anderson, Hendrix, Bowen, and uncounted other men created—is revealed in all its glory. Stars,
millions
of stars, seem to float above the disk. The focus of the disk creates an illusion: It seems as though there is nothing between the observer and the heavens. The great mirror has reached out and grabbed a chunk of the universe.

Few observers today use the prime focus. The last regular exposure of a photographic plate at Palomar was on September 29, 1989, almost forty years after Hubble exposed the “official” first plate at the prime focus on November 12, 1949. Photographic plates are still occasionally used on the two-hundred for late-epoch proper-motion measurements, but in the search for more sensitive detection devices,
astronomers shifted to phototubes, photomultipliers, and solid-state light-sensitive devices for most imaging and spectra. The black-box devices of the newest imaging technology are phenomenally sensitive, but they have stolen the mystique of developing a plate in the darkrooms around the perimeter of the observatory and wondering what results would emerge from the developing and fixing baths. The move from the prime focus to the Cassegrain focus, and now to the heated observing room, has stolen the romance of lonely nights aloft
in
the telescope, with the heavens laid out beneath the astronomer in the great mirror. Astronomers eagerly trade romance to reach ever farther into the universe.

In the 1970s an experimenter at the Bell Labs working on a new memory device for computers discovered that the silicon chips he was using were sensitive to individual photons of light. More experiments disclosed that these CCDs, or charge-coupled devices, were phenomenally sensitive, recording up to 90 percent of the light that hit them, compared to the 3 percent that even the most sensitive photographic emulsion recorded. The detectors were tiny, a few hundred pixels in each direction, compared to the millions of grains on a photograph emulsion. But a grain of a photographic emulsion is black or white. Each pixel of a CCD can record hundreds or thousands of shades of gray, as the sensitive chip electronically integrates the photons falling on its surface. The military promptly developed CCDs as detectors for spy satellites. The astronomers had to wait, until an enterprising astronomer and tinkerer from Princeton and Caltech named Jim Gunn found sample chips at an electronics surplus shop that had bought up rejected CCDs that didn’t meet military specifications.

Today CCD detectors are available even for amateur telescopes and video cameras. The electronic chips have revolutionized telescope research. Faint objects that could once be detected only in the two-hundred-inch telescope are now within the range of a one-meter telescope with a sensitive CCD detector.

In the basement shops in Robinson Hall, where instruments are built and maintained for the two-hundred-inch telescope, the electronic wizards stretch the capabilities of these new detectors. They combine supersensitive new CCD detectors with tiny Schmidt cameras and dispersion gratings. Another instrument uses fiber optics that can be manipulated so that in a single exposure, a large CCD can record spectrograms of hundreds of galaxies simultaneously, accomplishing in a fraction of an evening work that would have taken Hubble and Humason years. The new imaging cameras and spectrographs are so sensitive that the reach of the Hale telescope has doubled and doubled again, letting astronomers reach out to ever-more-distant galaxies and quasars, until they bump up against what seems a wall of detection, as if the telescope had finally reached the edge of the universe.

The CCDs feed their signals directly to a computer. The newest
instruments collect so much data, so rapidly, that for the next generation of detectors the coaxial cables that connect the instrument cage on the telescope with the computers will have to be replaced with a fiber optic pipe to provide adequate bandwidth for the data. With no need for an observer to change photo plates or manually focus the images for the plates and spectra, and with the image from a video camera to guide the telescope, observations are now done from a warm, brightly lit room on the mezzanine of the observatory. The night assistant and the observers sit in swivel chairs, controlling the telescope and the detectors from computer keyboards. Bags of Oreos and ever-available coffee have replaced the treasured midnight breaks when observers came down from their perch on the telescope to warm themselves with hot coffee or tea and share their sausages and cheese with the night assistant. A tape library that ranges from the Grateful Dead and Led Zeppelin to Bach and Mozart has replaced the AM radio the night assistants could pipe through the intercom to the prime focus, that sometimes mistakenly got stuck on a southern station broadcasting fundamentalist sermons for hours at a time.

Yet for all the new detectors and other improvements to the telescope, and the substitution of the warm data room for the cold perch in the observer’s cage, much of the operation of the telescope hasn’t changed. The strictest rule at the observatory, from the days when Ben Traxler became the first night assistant on the two-hundred-inch telescope, is that observers cannot move the telescope. The great machine is too valuable to trust to an astronomer. The night assistants aren’t necessarily engineers. One started out as a barber before finding his way to Palomar; another was a librarian. What they share is a respect for the instrument entrusted to their care, fascination with life on a lonely, beautiful mountain, and the skills to maneuver five hundred tons of machine.

The old control panel for the night assistant, developed from Sinclair Smith’s plans, is still in place, and still works, although for most use now, the motion of the telescope is controlled by a computer. At his console in the data room, the night assistant has gauges to monitor wind speed and direction, humidity, and the temperature at various points on the observatory and the telescope. Instead of turning dials to the observer’s coordinates, the night assistant types them into a computer keyboard.

It’s a long-standing tradition for the night assistant to make a ritual, several times each night, of going up to the balcony around the inside of the dome and then through the doorway to the balcony on the outside. From there, five stories off the ground, he (or she—even that has changed) can feel the humidity and view any threatening weather or run a hand along the brass handrail of the balcony. If the rail is wet with condensation, it is too damp to observe. It is then the night assistant’s responsibility to close the diaphragm over the mirror
until the air is drier or to shut the shutters of the dome if threatening weather appears.

Observers still go to the dome early in the evening, before dark, to calibrate equipment. Instead of hypering photographic emulsions, they refill the liquid nitrogen dewars (insulated flasks) on the CCD detectors, carrying a vacuum jug of super cold nitrogen up to the Cassegrain cage on the telescope. They get to the cage on a ladder that was modified from a war-surplus C-54 boarding platform. To make sure the ladder is out of the way when the telescope moves, it carries a plug that has to be secured in a wall outlet. Before the interlock system was installed, observers in the data room one night heard loud screeching during a run. When they finally came down to inspect, they discovered that the telescope had been dragging the heavy wheeled ladder with it as it slewed to different positions. There was no damage—a tribute to the robustness of the telescope—but no one likes to risk a priceless machine.

Before electronic instruments took over, the original Cassegrain cage, behind the mirror, had a swinging seat for the observer. An observation session, as the telescope slewed to new positions, felt like sitting in a gimballed drink holder on a boat.
^*
The gimballed chair was replaced in 1965 with a new cage, large enough to hold the huge new electronic detectors that had replaced photographic plates. The refrigerator-size instruments are packed with auxiliary lenses, CCDs, dispersion gratings, cooling dewars, and a mass of wiring and electronics. There was a time when astronomers studied optics and built their own instruments. Now, the “wizards” who build and maintain the instruments in the basement warren of offices in Robinson Hall practice magic that most astronomers don’t even try to understand. Fred Harris, who does much of the critical work on the CCDs, calls it a black art, part skill and experience, part luck. He eats a Mexican lunch “to steady [him]self” before he does critical work on a CCD, then does tricks with the sensitive chips that match Walter Baade or Milt Humason’s tricks with their photographic plates. Connections have to be soldered to connectors thousandths of an inch apart. Extreme vacuums and baths in oxygen are the equivalents of the plate-hypering an early generation used to increase the sensitivity of their photographic emulsions. Harris is the first to admit that he sometimes doesn’t know why the complex detectors choose or refuse to work. The early CCD detectors were mazes of wires and tubes for vacuum pumps, held together with miles of “Palomar glue,” duct and strapping tape. After years of refinements, the instruments are reliable. The ones not in use wait in
individual pens at the perimeter of the dome, labeled with names like “the four-shooter.”

Astronomers rarely discuss religion in the Monastery, but privately even veterans of years of observing runs on the big telescope talk of the awe-inspiring mystery of deep space observations, the inescapable feeling that every night on a big telescope is a unique voyage to an uncharted corner of the heavens. It is a magic moment when the night assistant flips switches on his console to start the telescope. From within the bowels of the observatory, a low rumble starts. There is no vibration, just the sound of the pumps for the oil bearings. The night assistant may say nothing more than, “The telescope’s ready,” but it is hard to shake off the feeling of starting on a vast voyage. Under the canopy of sky the huge dome and telescope feel tiny. It seems the height of audacity to think that this machine, five hundred tons of glass and steel, can reach out to the edge of the cosmos, that from a mountaintop on a planet circling around an ordinary star, one of billions in a not very special galaxy, we are about to reach into the secret depths of the universe.

When the telescope is ready, the night assistant types the coordinates of the first target of the evening into his console and follows with the command “Go.” As the telescope slews across the sky, images appear on the video display in front of the observer—stars, the fuzzy glow of a distant galaxy, the clear spiral of a near galaxy, the stellar gridlock of a cluster. Some observers talk of a new age of fully digital telescopes, when the observer won’t need to go to the observatory at all and can sit comfortably at a workstation at his home institution, typing commands and waiting for sample images to appear on his display. If the observer is halfway around the globe, even the time changes of nighttime observing disappear. The wee hours at Palomar are the working day in Europe or Asia.