COLUMN ONE : A Gleam of Hope for an Old Star : The Hooker Telescope on Mt. Wilson once ranked as the world’s biggest. Now, scientists see a way to rescue the mothballed marvel, as part of astronomy’s high-tech revolution.
To step into the Hooker Telescope dome is to step back in time. Antique cabinets stand next to hand-riveted truss work. Black Bakelite telephones rest on ancient oak desks. Wooden lockers still bear nameplates for Edwin Hubble, Fritz Zwicky and other long-dead legends.
“This is the most famous facility in the history of astronomy,” said Robert Jastrow of the Mt. Wilson Institute. Indeed, many scientists talk about the observatory above Altadena as a sort of astronomical shrine, the place where Hubble reshaped human consciousness by confirming the existence of billions of other galaxies and the expansion of the universe.
Eight years ago, however, science wrote off this venerable instrument.
Some said the Hooker was an astronomical anachronism, a museum piece with mirrors made out of French wine bottle glass during the First World War. Light pollution from brightly lit Los Angeles, and the advent of bigger telescopes elsewhere rendered the Hooker obsolete, they said.
But now, the telescope--made three generations ago with parts handcrafted by hammer and chisel--is about to be rescued by one of the very things that had threatened to kill it: modern technology.
Using the latest electronic sensors and image-enhancers--including a flexible glass mirror that can tweak the twinkle out of starlight--a group of scientists and philanthropists led by Jastrow are working to salvage the mothballed Hooker Telescope and restore a bit of the status it enjoyed during the three decades when it was the world’s biggest telescope.
Jastrow is a former professor at Columbia University and Dartmouth College and founder of the National Aeronautics and Space Administration’s Goddard Institute for Space Flight. He has raised $250,000 in donations to rebuild the telescope’s mercury suspension and make other repairs. He is seeking another $250,000 for the electronic gear needed to make it useful into the 21st Century.
The bare-bones effort to resuscitate the 76-year-old, 100-inch-wide Hooker illustrates just how far computers and other electronic gizmos are transforming astronomy, a science that until now had changed little since Galileo and Newton first turned telescopes heavenward more than three centuries ago.
“New technology is having a profound impact on astronomy,” said physicist Charles H. Townes of the University of California. “It lets us see better, farther--and see it all faster--than ever before.”
Boston University astronomy professor Michael Mendillo said the profusion of new electronic devices, from supersensitive cameras to robotic telescopes that can take and evaluate hundreds of pictures automatically, are responsible for “a dramatic revolution” in the study of the universe.
These innovations affect virtually every step in the study of stars, from how starlight is collected to the way it is recorded and the way scientists analyze it--even how they think of it.
The picture of an astronomer spending all night peering into a telescope eyepiece or making a long photographic exposure is going the way of the slide rule. Now, astronomers are more likely to be found in front of computer screens, comparing digitized images that have been manipulated to eliminate the twinkling caused by atmospheric turbulence, then filtered or otherwise enhanced by computer before being recorded for permanent storage.
“Most big telescopes no longer even have eyepieces,” said Ian McLean, a UCLA professor of astronomy and physics.
Astronomers are no longer required to work at night or even to visit some telescopes. Observatories increasingly use computers to aim telescopes that digitally record images while astronomers sleep. These pictures, once digitized, can be transmitted over telephone lines.
This capability also is opening up the world’s great telescopes to high school students, who can tap into these images with a personal computer. One University of Tennessee program on Mt. Wilson shares images with students in its home state. A program offered by Lawrence Livermore National Laboratory in Northern California permits students to program a UC Berkeley telescope from their classrooms.
These new tools are not only changing how astronomers conduct their research, but what they can look for and even how they are trained.
“Astronomers today are really applied physicists,” said McLean, who has written a book on the electronics revolution, “Electronic and Computer-Aided Astronomy: From Eyes to Electronic Sensors.”
“We used to have to know optics and some basic observational skills, but now astronomy is a much different field,” said John N. Bahcall of the Institute for Advanced Study at Princeton University. “It is a much more experimental science now. It resembles physics or chemistry much more than it once did. . . . Now you can’t imagine anyone considering any data that is not first processed by computers.”
Astronomers around the world--from great observatories in Hawaii, Arizona and Chile to ambitious amateurs in their gardens--are eagerly experimenting with these innovations.
On Mt. Wilson, astronomers are counting on new electronic devices to help them overcome shortcomings and enhance the strengths of one of the world’s biggest and most famous telescopes.
The Hooker’s most glaring weakness is its proximity to Los Angeles, a megalopolis of several hundred square miles of street lamps, signs, parks and other sources of light. These lights pollute the night sky and wash out all but a relatively few bright stars and planets.
Light pollution was one reason the Washington-based Carnegie Institution decided in 1985 to close the Hooker Telescope and phase out support of the Mt. Wilson Observatory in favor of an observatory on a remote mountain in Chile. Tight budgets and the telescope’s age also contributed to the decision.
Astronomers disagree about whether age alone is a problem.
Eric Becklin, an astronomy professor at UCLA, said the instrument “should be a museum” because its antiquated mechanics are not suited to modern research.
Elizabeth Griffin, a research fellow at Cambridge University, conceded that the facility is old-fashioned, but said: “What’s wrong with old-fashioned when it can do better than modern equipment?”
The question of whether a large reflecting telescope--one with a primary mirror at least 98 inches in diameter--can become hopelessly antiquated is a new issue. Only four of the world’s 23 large telescopes were built before 1970; the Hooker is the only one predating World War II. Another 13 are being built, reflecting a boom in optical and infrared astronomy that has been encouraged by electronics.
“Not only is (the Hooker) viable,” said USC astronomy professor Edward J. Rhodes Jr., “but there are some projects particularly suited to what it can do.” Among them, he said, is the new field of helioseismology, which analyzes vibrations in stellar gas to deduce the inner workings of stars.
Griffin, Rhodes and others said the Hooker’s best features are not the admittedly antique sets of gears and pulleys that control its movements. Its real value is in the thin layer of aluminum on its huge mirror--and the promise of boosting its natural light-gathering power with such new tools as solid-state light sensors called charge-coupled devices (CCDs).
A much more sophisticated and sensitive version of the key component of home video cameras, CCDs are 40 times more sensitive to light than the photographic emulsions that scientists have used since the 1800s. The best CCDs can see stars that are 100,000 times fainter than the night sky. CCDs also are easier to use, faster and more accurate than photomultiplier tubes and other crude electronic detectors that scientists have experimented with since the 1950s.
Because CCDs deliver data digitally--as a series of electronic pulses instead of gray tones in a photograph--they make it much easier for computers to swiftly sift very faint or distant objects out of background light, Bahcall said. And because they detect light quickly, he added, CCDs let astronomers cover more of the sky in less time.
“Without getting rid of the light (from Los Angeles), we can suddenly go beyond it,” said Sallie Baliunas, deputy director of the Mt. Wilson Institute and a solar astronomer at the Harvard-Smithsonian Center for Astrophysics.
“The impact of CCDs has just been astounding,” said Boston University’s Mendillo. “Every observational astronomer in the world wants to take their data with CCDs . . . because you can manipulate data in so many interesting and creative ways.”
“It has completely revolutionized optical astronomy, but perhaps an even greater revolution in infrared astronomy is riding on its coattails,” said McLean, who runs the Infrared Imaging Detector Lab at UCLA.
Infrared astronomers once settled for reconstructing images by recording infrared light one point at a time, a process McLean called “tedious, time-consuming and prone to errors.” Now, he said, these scientists can use CCD-like direct readout chips to snap whole infrared images comparable in quality to ordinary photographs.
The sensitivity of these electronic sensors has permitted some remarkable research. Bahcall said it takes a minute to estimate the speed at which another galaxy is receding from the Milky Way; before CCDs, such estimates required 20 hours each. Mendillo said he was able to detect and describe the moon’s ethereal sodium atmosphere because a CCD let him digitally subtract background light; previously, ground-based telescopes had not detected a lunar atmosphere at all.
Scientists agree that the Hooker Telescope should reap similar benefits.
“The robustness of the results could be much better than they were before,” Bahcall said. “It is the difference between impressionist painting . . . and photography.”
Jastrow and Baliunas expect equally impressive benefits from an even newer electronic tool, adaptive optics, because it could enhance Mt. Wilson’s storied “seeing” conditions.
Mt. Wilson offers North America’s sharpest sky views because the atmosphere over it is very still. Potential sources of turbulence, such as heat and smog, are trapped at the surface by an atmospheric inversion layer before they can rise and jumble starlight. Thus, objects bright enough to be seen despite light pollution from the city are seen in exceptional detail.
Adaptive optics could improve conditions by correcting for the effect of high-level winds and the turbulence they cause.
The system, developed by the Air Force to spot ballistic missiles in space, does this with a small, computer-controlled flexible mirror. A wave-front sensor measures the blurriness of a star’s light, then passes the information to a computer that decides how to “deform” the mirror to bring the image into focus. Because the atmosphere constantly changes, this must be repeated hundreds of times each second.
When the system works well, it allows astronomers to see details in bright stars they never saw before. It also concentrates light from very faint objects into a single spot, making them easier to see.
“With adaptive optics, you can resolve or ‘see’ an object much, much faster,” said Edward J. Kibblewhite, a University of Chicago astronomer and adaptive-optics pioneer.
Adaptive optics is new to astronomy. It was declassified only three years ago, and all of the handful of astronomical units operating--including a Massachusetts Institute of Technology model attached to the 60-inch telescope at Mt. Wilson--are jury-rigged experimental setups.
But astronomy professor Laird N. Thompson at the University of Illinois at Champaign-Urbana said that ground-based telescopes fitted with adaptive optics can detect infrared and visible light “as good as or better than the Hubble Space Telescope.”
Electronics are even improving telescopes in an old-fashioned way: by allowing engineers to build bigger “light buckets.”
For example, University of California and California Institute of Technology astronomers at the Keck I telescope in Hawaii are using a computer to steer an array of 36 hexagonal mirrors so that they capture and focus starlight as if they were a single mirror 386 inches in diameter.
Meanwhile, European astronomers at the New Technology Telescope in Chile rely on a computer to prevent that observatory’s ultra-thin, ultra-light, 137-inch-wide mirror from being distorted by gravity and temperature changes.
Others are starting to explore using electronics to combine visible and infrared light from two or more telescopes to make a single image with unprecedented detail. This approach, called interferometry, had been limited to radio telescopes.
Computers and other new electronic devices “will let us go fainter--to look at stars that are farther away or just dim stars that are not very luminous,” said Harold A. McAlister, an astronomy professor at Georgia State University. “This will take us to all sorts of places we haven’t been.”
BACKGROUND
Opened in 1917, the Hooker Telescope on Mt. Wilson was the largest in the world until 1948, when the 200-inch Hale Telescope opened on Mt. Palomar in San Diego County. It was the world’s sixth-largest telescope as recently as 1975 and now ranks 22nd. The Hooker Telescope was named for Los Angeles businessman J.D. Hooker, who in 1906 gave scientist George Ellery Hale $45,000 to buy the 100-inch-wide mirror that is the heart of its magnifying and light-gathering power. The Carnegie Institution in Washington, D.C., which built and ran the observatory for 81 years, mothballed the telescope in 1985, citing obsolescence and light pollution from Los Angeles.
Star Search
In the world of telescopes, bigger is not always better. Even the world’s largest telescopes cannot see fine detail any better than a hobbyist’s instrument because turbulent air bends light, fuzzing what is seen on the ground. This makes stars twinkle, but hampers research. New computer-controlled flexible mirrors, or “adaptive optics,” are being used to correct for this.
BEFORE
Atmospheric turbulence causes a star’s image to become blurry and hard to study. Usually the most astronomers could hope for was a fuzzy blob.
AFTER
How adaptive optics is being used to correct for atmospheric turbulence.
1) Astronomers measure turbulence with a “wave front detector” that senses slight changes in the direction light moves. This technology works best with bright objects, so they make this measurement by looking at a “guide star” near the area they want to explore.
2) A computer studies the bent light waves and determines how to straighten them by deforming a small flexible mirror.
3) Light waves from the target star are bounced off the deformed mirror, bringing the image into much sharper focus than previously possible. Since the atmosphere is in constant motion, the process must be repeated hundreds of times each second.
A FLEXIBLE MIRROR
The mirror is deformed by dozens of tiny push-pull pistons or quartz crystals that change their shape when subjected to an electric current.
ADAPTIVE OPTICS: A new field of vision
Background: Adaptive optics was developed by the Defense Department in the 1970s. The Air Force refined it for use as part of the Strategic Defense Initiative to detect incoming nuclear warheads.
What’s next: Lawrence Livermore National Laboratory researchers are experimenting with using laser beams to illuminate a natural sodium gas layer in the upper atmosphere, creating a false guide star. This would let astronomers use adaptive optics in parts of the sky that do not have bright stars nearby.
Sources: Lawrence Livermore National Laboratory, Mt. Wilson Institute
