A new generation of ``supertelescopes'' being designed for mountaintops around the world could usher in a Golden Age of astronomy by the early 1990s. At least seven mammoth optical telescopes -- four on drawing boards in the United States -- are now being planned, each of which will have more than twice the light-gathering capacity of today's biggest devices.
The instruments are expected to be able to peer deep enough into space to yield new clues about the origins of the universe. Because light from space takes time to reach Earth, the farther out astronomers probe, the farther back in history they see.
They may also help resolve a host of other cosmic conundrums: the birth of planets, the mysteries of quasars (starlike objects that emit light or radio waves), and the dynamics of infant galaxies.
``It would represent a truly Golden Age -- a renaissance for astronomy,'' Robert D. Gehrz, a professor of physics and astronomy at the University of Wyoming, says of the proposed projects.
Behind the spurt in jumbo telescopes are several radical new ideas on how to build them. Ever since the dedication of the 200-inch Hale telescope -- still the world's premier optical device -- atop California's Mt. Palomar in 1948, astronomers have thought they had reached the technical and financial limits of big-telescope construction.
The reason: the mirrors. They effectively determine the power of a telescope. The bigger the reflector is, the more light it can collect from objects in space. Yet a mirror much larger than Hale's wouldn't hold its shape, because of its weight.
Astronomers have been able to offset this problem somewhat with advances in light-detection systems. Electronic detectors now record more than 60 times the number of photons (massless subatomic particles that transmit light) collected by mirrors than those of 20 years ago. But advances in these systems are fast approaching their limits. Thus the need for bigger telescopes altogether.
One emerging idea is to use many pieces of glass fit together, like a mosaic, instead of casting a single continuous concave surface. A version of the approach, devised by astrophysicist Jerry Nelson and colleagues at the University of California, is to be used in the new Keck Observatory.
This 390-inch telescope is likely to be the first of the new extra-large instruments to come on line, thanks to a recent $70 million grant from the W. M. Keck Foundation. If completed by 1992, as envisioned, the Keck telescope would be the world's largest -- nearly twice as big as Palomar and capable of detecting a candle on the moon. Developed by the University of California and the California Institute of Technology (Caltech), it will sit atop koa-studded Mauna Kea, an extinct volcano in Hawaii.
The main mirror of the telescope will contain 36 hexagonal pieces, each 6 feet wide and 3 inches thick. A computerized positioning system will keep them moving in concert, with up to 100 adjustments possible each second, down to 1/1,000 the width of a human hair. Although not yet tested on a large scale, the ``segmented mirror'' scheme should yield other benefits as well. Because the mirrors can sit on lighter supports, the 10-meter telescope will probably weigh less than one-third of the Hale telescope. A shorter focal length -- and thus a stubbier barrel -- will mean that a smaller dome can house it. (Domes can account for one-half the cost of an observatory.)
Yet, as Caltech president Marvin Goldberger noted when funding was announced in January, the instrument should still have enough power to peer back in time ``12 billion years, nearly three-quarters of the period back to the birth of the universe.''
A different optics arrangement altogether is being envisioned for an even-bigger device, the National New Technology Telescope (NNTT), which would be federally funded and perhaps perched on the same volcano crest. It calls for a mirror arrangement similar to that used successfully in the much smaller multiple-mirror telescope outside of Tucson, Ariz. The idea is to mount mirrors like guns on a ship: With the NNTT, four 295-inch reflectors would sit on a common mount. They could be used individually or their images combined optically to serve as one jumbo eye.
Perhaps more unusual than the arrangement, however, is the novel design of the mirrors themselves. They would not be monolithic glass slabs but thin sheets supported by a hollow honeycomb.
The method for fabricating the mirrors was devised by Roger Angel at the University of Arizona. One technique he uses is to put molten Pyrex into huge vats in a rapidly spinning oven so the liquid will climb the sides and form a natural parabola. Thus, less grinding and polishing are needed -- a process that once took years.
So far the method has been tried only on small reflectors. But now the University of Arizona is building a massive rotating oven and special grinder beneath its football stadium to cast mirrors of up to eight meters in diameter. This facility would be used to make the optics for the NNTT -- if Congress votes to fund the project (no certainty).
These are not the only telescopic titans on astronomers' drawing boards. The University of Texas has been scouting funds for a similar-size telescope, which would use either an Angel honeycomb mirror or a design of its own that resembles a huge contact lens. Japanese astronomers are looking at Mauna Kea as a possible site for a 295-inch instrument. West European countries are considering plans for an array of four separate telescopes in Chile.
The Soviet Union, meanwhile, continues to harbor ideas for a 25-meter behemoth using more conventional design techniques.
How soon any of these giant instruments comes on line will hinge on funding and solutions to the usual technical problems that develop during scale-up. Astronomers argue that all are needed, despite plans for a new space telescope and other instruments soon. They note that different telescopes perform different tasks, and they point to the sheer number of cosmic riddles demanding attention. Drawings: Stronger spyglasses on the sky Innovative designs in mirrors will open up new windows on the universe, allowing astronomers to peer at objects billions of light years away. The new-generation telescopes, although vastly more powerful than today's biggest instruments, will fit in smaller domes as a result of unusual design techniques. One of the new telescopes is expected to be able to detect the light of a candle from the distance of the moon. Hale Observatory: Completed in 1948 200-inch single mirror. Although 37 years old, this instrument in Mt. Palomar, Calif., is still the world's premier optical telescope. Its monolithic concave mirror was considered the biggest that could be practically built using conventional construction techniques. Keck Observatory: Planned completion date: 1992 390-inch, segmented-mirror-type system. Location: Mauna Kea, Hawaii National New Technology: Telescope (NNTT) Planned completion date: early 1990s. 590-inch, multiple-mirror design. Possible site: Mauna Kea, Hawaii National New Technology: Telescope (NNTT). Planned completion date: early 1990s. 590-inch, multiple-mirror design. Possible site: Mauna Kea, Hawaii The proposed Keck telescope will feature a primary mirror made up of 36 hexagonal segments, each independently adjustable to act in concert like a near-perfect parabola. It will be mounted like a large naval gun and will rotate on its base. The NNTT will be made up of four 290-inch mirrors, each cast as a honeycomb similar to the six-foot lens shown below. Using such a hollow structure to support the mirror, designers will be able to avoid the cost and weight problems associated with making one solid slab of glass.