Dawn of a Big Telescope

Abstract

F ourteen thousand feet above sea level, the summit of Hawaii's Mauna Kea commands a panoramic view of ocean, sky and extinct volcanoes. High above treeline, where the air thins and even simple tasks can require special effort, the summit's barren, windswept landscape of brownish-red volcanic ash presents an otherworldly appearance. Astronomers liken the terrain to depicted by Voyager images of Mars. A fitting site, perhaps, for a new optical and infrared telescope the world's largest-that bucks traditional designs in an attempt to probe distant stars and galaxies inexpensively but accurately, collecting more than any of its predecessors. Like pieces of a highly polished jigsaw puzzle, 36 hexagonal mirror segments each measuring 1.8 meters between opposing vertices and fitting into a particular section of a honeycomb-shaped steel frame will form the 10-meter mirror of the W M. Keck telescope, now under construction on Mauna Kea and scheduled to begin full operation late next year. With the nine of Keck's mirror segments assembled and moving as a single unit thanks to a complex array of computer-controlled pistons, springs and sensors, researchers expect to release next week the telescope's first light images marking a milestone in the sometimes turbulent 13-year development of the instrument. Debate continues over the wisdom of using segmented mirrors as opposed to one of the new, relatively lightweight but still untested single-unit primary mirrors planned for six other large telescopes slated for completion later in the 1990s. Nonetheless, many astronomers agree Keck will help to usher in a new age of big astronomy cT think [Keck] is going to drag astronomers kicking and screaming into the modern era of electronically controlled telescopes, says veteran astrophysicist John N. Bahcall of Princeton University While not affiliated with the Keck project, Bahcall has a poster of the telescope on his office wall. I'm waiting breathlessly for the results, he adds. Bahcall expects the Keck telescope to help solve a number of cosmological mysteries that we couldn't address before because we didn't have a big enough telescope. He cites as one example Keck's expected ability to detect the absorption spectra of quasars now too faint to be seen accurately by the limited light-gathering area of existing telescopes. These spectra provide fingerprints of the types of material through which quasar passes on its way to Earth. Bahcall says Keck's 10-meter primary mirror will also help to trace the evolution of galaxies over billions of years, from the time they formed after the Big Bang. Using Keck to detect the spectra from faint, ancient galaxies, and comparing these spectra with those of a set of brighter, newer galaxies closer to Earth, may help reveal how closely the chemical composition of older objects resembles more recently evolved galaxies. Analyzing spectra may also provide astronomers with the true redshift of a galaxy or quasar, a key tool not only for determining the distance to objects outside the Milky Way, but also for calculating the expansion rate of the universe. Garth D. Illingworth, an astronomer at the University of California, Berkeley, and cochairman of the Keck Science Steering Committee, notes the telescope's enhanced infrared resolution should provide new details about star formation, and may also discover planets orbiting