Better Spyglass on the Stars

By Natalie Angier

The towering Mauna Kea, a 13,800-ft. extinct volcano in Hawaii, is a peculiar mix of the exotic. Gnarled koa trees twist up from its tropical slopes, where the endangered palila bird, a tiny yellow honey creeper, crushes rock-hard mamane seeds with its beak. But up on top, science has taken over. Because the exceptionally dry and stable atmosphere over Mauna Kea makes the site among the world's best spots for star gazing, six telescopes have been built on the volcano's crest, and two more are under construction.

Now an extraordinary newcomer will join that celestial company. The California Institute of Technology, working with the University of California, will build the world's biggest optical telescope on the volcano's crest; construction could begin as early as 1986. The mammoth instrument, made possible by a $70 million grant to Caltech by the W.M. Keck Foundation, will have an innovative mirror system nearly 400 in. in diameter, which is twice the width and has four times the light-gathering capacity of today's reigning optical telescope, the 200-in. Hale device at Mount Palomar, Calif. When astronomers begin using the new telescope in 1992, it will push back the visible limits of the universe by billions of light years. Says Howard Keck, president of the foundation: "I'm told it will permit one to see the light of a single candle from the distance of the moon."

The Keck telescope, as it will be called, is the first of a new generation of extra-large telescopes designed to overcome construction problems that have dogged sky gazers since before the Hale was dedicated in 1948. Photons (massless particles that transmit light) from an ancient galaxy may travel billions of light years through space before they speed down a telescope tube. But unless enough of them are collected, astronomers will not be able to see the galaxy's image. Gathering sufficient photons to register an image is accomplished by either taking long-exposure photographs or using a larger mirror system to collect the light. Many astronomical photographs already take hours to make, but even then not enough photons can be gathered for a clear view of very faint objects. Hence the need for bigger mirrors. Complains Palomar Observatory Director Gerry Neugebauer: "We're photon starved."

Yet conventional telescopes cannot be simply scaled up indefinitely. As the mirrors get bigger, they begin to sag under their own weight. Indeed, for years many astronomers believed that a 200-in. diameter was the practical limit for an optical telescope.

The advent of the computer has changed all that. Led by Astrophysicist Jerry Nelson, a team at the University of California designed an unorthodox mirror that will not be a continuous concave surface, like Hale's, but 36 hexagonal pieces of specially shaped glass, each 6 ft. across and 3 in. thick; the segments will be fit together and will move in concert to act as one giant parabolic mirror. That harmony is possible only with the aid of a computer- controlled sensing and positioning system, which will realign the components 100 times a second by as little as one one-thousandth the width of a human hair.

Other design innovations follow in trickle-down fashion. Because a segmented mirror requires a much lighter support than a conventional one, the Keck telescope will weigh only 158 tons, a third the weight of the Hale instrument. Yet it will be able to perform miracles like taking infrared photographs that are 50 to 100 times sharper than any ever before made on earth. Says Caltech Astronomer Maarten Schmidt, famed for his discovery that quasars are the most distant and energetic objects ever observed: "In all aspects, a big telescope can do things better and faster than a small telescope."

Keck is only one of many telescopic brobdingnagians now in various stages of development around the world. In Tucson, scientists at the National Optical Astronomy Observatories (N.O.A.O.) and the University of Arizona are working on still another novel optics scheme: four 295-in. mirrors placed on a common mount. Each mirror would be 2 ft. thick but largely hollow, shaped like a honeycomb. The four could either be used in tandem, creating the equivalent of a gigantic 590-in. mirror, or separately. Overseas, Japanese astronomers also have their eyes on Mauna Kea; they hope to build a 295-in. telescope on the volcano by the 1990s. The European Southern Observatory, headquartered in Munich, is considering an array of four 315-in. telescopes that could, like the N.O.A.O. instrument, act in concert.

Through Keck, the space telescope and other new devices, astronomers hope to get a closer look at a myriad of cosmic quandaries: quasars; pulsars, the spinning neutron stars that transmit precisely spaced radio pulses; and the dusty smudges around some stars, which could be the beginnings of planetary systems much like the sun's. And because light from space, traveling at 186,000 miles a second, takes time to reach the earth, the deeper into space astronomers can probe, the farther back into the past they can see. Says Schmidt: "By looking farther out in the universe, you are paging back in the history books, as it were, to Time Zero." Once they reach that ineffable edge, the scientists may better understand where the universe came from, and where it is going. Or they may end up more baffled than before. Says Nelson: "Probably the most exciting things we'll discover are the things we haven't thought of yet."

With reporting by Carol Foote/San Francisco