New scopes give clearer view of origin of cosmos
Opening of Subaru telescope on Hawaii is latest example ofinternational demand for giant mirrors and new technologies.
MAUNA KEA, HAWAII — On the slopes of Mauna Kea, 2-1/2 miles above the beaches of the Big Island, a group of Japanese astronomers crowd into dark room vaguely reminiscent of Oz. In the living-room-size chamber, computer monitors and TV screens line the walls, giving only a hint of what looms behind the scenes.
Nearby, a mirror broader than a two-lane highway and heavier than four Learjets is angled toward the sky, taking its first look at the heavens. With it, astronomers will look farther into space than humans ever have before, peering into the origins of the universe. Indeed, by looking at galaxies and cosmic building blocks 14 billion light years away, researchers have an opportunity to see the universe as it existed near the time of the "big bang."
"We are now able to look at the edges of the known universe and to look far beyond them," says Ian Shelton, an astronomer with the telescope, called the Subaru, which opened last week. "It's incredibly exciting."
A project of the National Astronomical Observatory of Japan, the Subaru - the Japanese name for the star cluster also known as the Pleiades - is Japan's entry into a new kind of space race. Around the globe, enormous telescopes using pioneering technology are being built at an unprecedented rate. From Arizona, where new mirrors are being structured like honeycombs, to Chile, where a 27-foot-wide mirror has been forged from a single piece of glass less than one foot thick, these telescopes herald a new golden age in earthbound astronomy.
"I have had questions that needed answering for 20 years that were out of reach of the smaller telescopes," says Catherine Pilachow-ski, an astronomer with the US National Optical Astronomy Observatories. "Now, I can finally get some answers." Any star in our galaxy "is within the reach of these new telescopes."
For a half century, the 16-foot-wide mirror on the Hale Telescope at Palomar Observatory in California set the standard for telescopes. But scientists knew that, theoretically, bigger telescopes would produce dramatically better images and gather much more light. A telescope with a 27-foot-wide mirror - such as the Subaru or the one in Chile - gathers almost three times as much light as the Hale.
"If you have a telescope that is twice as big, you can actually produce an image twice as sharp," says astronomer Neville Woolf of the University of Arizona in Tucson, a large-scope pioneer.
But the technical barriers were tremendous. Larger mirrors tend to be more adversely affected by temperature changes than are smaller ones, resulting in warped, fuzzy images. Astronomers did not know how to minimize distortion caused by Earth's atmosphere. And the computing power needed to control all facets of such large scopes was not readily available. "Astronomers had to know they could get good images with the very large telescopes before they would build them," says Dr. Woolf.
Over the past 20 years, however, these obstacles have been overcome. The development of super strong ceramic and glass materials highly resistant to temperature changes allowed for thinner reflective surfaces, making larger mirrors more feasible. Military research into satellite tracking produced innovative computer systems that minimize image distortion. And perhaps most important, computers technology to control the scopes has improved vastly.
"Underlying an awful lot of this has been the tremendous progress in computing," says Woolf. "We used to think that the process of guiding a telescope was someone looking through the eyepiece and then pushing a button. That's an incredibly poor use of a trained PhD."
Thus far, teams building large scopes have taken three approaches: segmented mirrors made out of dozens of separate but closely aligned hexagonal mirrors; single-piece mirrors (like the Subaru); and honeycomb spun-cast mirrors - which use hollow, single-piece mirrors.
To maintain curvature and compensate for the tug of gravity on these massive mirrors, computer-controlled sensing systems direct hundreds of actuator arms (pistons). These sensitive devices can manipulate the curvature of the relatively floppy mirrors to within degrees of accuracy far finer than the width of a human hair. As for the hollow honeycomb mirrors, they also allow astronomers to maintain the optimal mirror temperature by pumping air into the mirror itself.
Still, scientists are struggling to perfect these telescopes, which are far more difficult to use then their smaller brethren. And no one is certain how consistently good images from large telescopes will be over time. "With a larger instrument, you have to do more tricks to make it do something quite simple," says Chris Simpson, an astronomer with the Subaru Project.
Regardless, the new telescopes should increase the number of dramatic discoveries. Significantly, the Subaru scope includes some of the most advanced infrared technology available. It will enable the scope to detect light at the farthest reaches of the universe - which can only been seen in the infrared.
Another advance includes the Large Binocular Telescope under construction in Arizona. It will use twin 27-foot honeycomb mirrors mounted side-by-side to create an image equivalent in clarity to that of a 55-foot mirror scope.
The success of the Hubble Space Telescope also has astronomers plotting a next generation of space scopes. "Already, as we push into this very large telescope era, the costs of giant space telescopes and giant ground-based telescopes are starting to converge," says Woolf.