Bigger & Brighter

Ever since Galileo taught them to scan the skies with a telescope, astronomers have studied the sun with particular interest. It is the earth's own star, and to earth-bound viewers it glitters with 10 billion times the brightness of any other celestial body. Everything significant that happens on the sun--the emergence of solar flares, for example--signals some effect on the earth's atmosphere.

But even as their sun telescopes have grown larger and more powerful, the sun studiers' problems have grown more complex. When the National Science Foundation set out to build the world's largest solar scope six years ago, a massive investigation had to be made merely to find where to place the monster. Astronomers roamed the U.S.; rockets were fired aloft to check on atmospheric conditions; scores of aerial maps were made before the NSF settled on 6,875-ft. Kitt Peak in Arizona. The peak's flat top, high in the clear air, is well above hot desert breezes, but not so high that ice will become a problem. And above it the atmosphere is relatively free of dust and clouds.

But how to build a giant telescope with a focal length of 300 ft.? Any such mammoth construction high on an exposed peak would surely be swayed by winds, would tremble with the earth's least vibration. The cumbersome structure could hardly serve for delicate solar observations. The astronomers solved that problem by digging down, not building up.

They bored a slanting shaft deep into their mountain (see diagram). Above the shaft they mounted a heliostat (a flat mirror). As the mirror turns to follow the sun across the sky, it reflects the sun's rays down the shaft where they are reflected back and focused by a concave mirror. Bounced back toward the top of the shaft, the light is intercepted at ground level by another mirror and angled into a vertical well. There the sun's image can be examined on a flat screen, photographed, or studied with a spectrograph.

With the aid of their spectrograph, the solar scientists will be able to analyze small segments of the sun's light, satisfy themselves as to just what elements are burning with such fierce brilliance. Hopefully, such analyses will give them new insights into the violent physical changes that take place in sunspots and perhaps even in the deep core of the sun itself.

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