Six New "Eyes" On the Sky

An extraordinary telescope nears completion

Located atop a parched, rocky mountain some 40 miles south of Tucson, Ariz., the squat, rectangular building with the gaping hole in its sides and roof looks like a space-age barn. In fact, the strange structure is somewhat out of this world. Now in its final stage of testing, it is the prototype of a new generation of giant optical telescopes that could open fresh vistas on the heavens -- and, by astronomy's standards, at bargain-basement prices.

A joint project of the University of Arizona and the Smithsonian Astrophysical Observatory, the extraordinary telescope, unlike other reflectors, does not use a single primary eye on the sky. Instead, it has six main mirrors, ,JS each with a diameter of 1.8 meters (72 in.). Arrayed in a circle and directing their light on a common focus to produce a single image, they gather as much light as a traditional 4.5-meter (176-in.) instrument. Thus, the so-called Multiple-Mirror Telescope is exceeded only by Palomar's 5-meter (200-in.) mirror and the new Soviet 6-meter (240-in.) telescope.

Why six mirrors when one would do? Because it is far easier to cast, grind and mount several small mirrors than one huge one. At $8 million, MMT's cost was a fourth of a comparable conventional telescope's price.

The basic idea for multi-eyed monsters is not new. Even while they were building Palomar in the 1930s, astronomers realized that if they wanted still larger instruments they would need less expensive technologies. Yet many doubted that it would ever be possible to get several smaller mirrors to scan the heavens precisely in unison. Explains MMT's acting director, Neville Woolf: "The problem is comparable to getting six headstrong prima ballerinas to dance as if they were one."

In 1970, Arizona and Smithsonian astronomers joined forces on just such a telescope. Its locale: the summit of Arizona's 2,600-meter (8,500-ft.) Mount Hopkins.

There was great need for the instrument; with their field undergoing explosive growth, U.S. astronomers were already waiting a year or more for a few precious days' viewing time on one of the nation's handful of major telescopes. MMT's builders had another incentive: the Air Force had available a number of lightweight 1.8-meter blank mirrors, presumably discards from its spy-satellite program.

Five years in building, MMT incorporates many design innovations. All six mirrors, plus a small .8-meter (30-in.) guide telescope in the center of the cluster, are mounted on a single Y-shaped yoke that tilts and turns like a gun mount. Rather than a traditional dome, MMT's designers opted for a cheaper rectangular Y OF ARIZONA building that rotates with the telescope. A small moat keeps out dust and stray snakes, scorpions and rats. Yet MMT'S most unusual feature is its internal laser tracking system. It enables all six telescopes to follow the same object across the skies with an accuracy of . 1 second of arc, I roughly equivalent to keeping a quarter in the cross hairs of six separate gun sights at a distance of about 25 km (15 miles).

All six MMT mirrors have been exposed to what astronomers call "first light," and the new instrument should be operational by early next year. For astronomers, the heavens can hardly wait. Because of MMT'S high and dry desert perch, it should be highly effective in exploring the skies in the largely neglected infra-red portion of the spectrum. These longer wave lengths are especially useful for studying such cosmological mysteries as the birth of stars and the violence in the heart of distant galaxies and quasars that may well be caused by those baffling black holes.

This file is automatically generated by a robot program, so viewer discretion is required.