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It was apparent to Borra that modern technology, in the form of a precise synchronous motor to turn his mirror and nearly frictionless, vibration-free air bearings to support it, could solve the mechanical problems. And he realized that despite the mirror's pointing limit, there would be a legitimate use for it. "If your study is cosmology, the origins and nature of the universe, it doesn't matter where you look," he says. "There are data to be found anywhere you aim a telescope."
Although pointing only straight up, the telescope at any given moment covers a region of sky twice the width of the full moon and, as the earth turns, scans a narrow but long band of the heavens. With many liquid telescopes set up at different latitudes, says Borra, astronomers could map the locations of the faintest, farthest galaxies, find out how they are distributed in space and thereby learn a great deal about the structure and evolution of the universe. Or they could take a brief exposure of a particular galaxy each night, store the image digitally, then add to it with exposures on following nights until enough data had accumulated to reveal previously unseen details.
When Borra began building a working model in 1982, another advantage of the concept soon became apparent. The 40-in. model cost him less than $7,500 (U.S.), and he has a grant of $22,500 from the Natural Sciences and Engineering Research Council of Canada for a 60-in. version now under construction. Says Borra: "I think that we could build a liquid mirror telescope as large as 30 meters [1,181 in.] for $7.5 million." By contrast, the 400-in., 36-segment mirror alone for the Keck Telescope, to be erected in Hawaii, is expected to cost $25 million.
Borra reports that other astronomers have taken notice of his venture: "They've said, 'It's an interesting concept—now show us." Although Roger Angel, head of the University of Arizona's Steward Observatory Mirror Laboratory, has not given up on larger glass mirrors (his team has designed an inexpensive 312-in. mirror with a unique honeycomb structure to keep it light), he calls the liquid-mercury project "very challenging. If it can be done at 30 meters, it be comes unique in its grasp of light. There are problems in astrophysics that would lend themselves to this kind of telescope."
Many challenges still await Borra. "It is simply more difficult to build things bigger," he says. "We would have to build bigger turntables and mount them on bigger bearings. We would have to use bigger motors to turn them, and we would encounter problems of weight." Surface ripples present another problem, but a thin coating of oil suppresses them. The layer of tarnish and dirt that slowly dulls the mercury's reflective surface is easily skimmed off. Says Borra: "We've proved the hardest thing: you can make an astronomical-quality mirror out of liquid mercury. These mirrors won't give us answers to the ultimate questions about the origins of the uni verse, but they should help us understand enough so that we can ask these questions."