Computerized Star

Through telescopes or high-powered binoculars, most of the solar system's planets appear as disks, some with distinguishable surface features. But stars other than the sun are so distant that even the closest one* looks like a mere pinpoint of light through the most powerful telescopes. Now astronomers at Arizona's Kitt Peak National Observatory have improved the stellar image. Using their new 158-in. reflector--the world's second largest telescope--in combination with a novel, computer-enhanced photographic technique, they have produced the first pictures of a star that show some surface detail.

The star is Betelgeuse, a so-called red giant so large that it could encompass the inner solar system almost all the way out to the orbit of Jupiter. On a clear night last March, Astronomers Roger Lynds, Jack Harvey and Peter Worden took some 40 photographs of Betelgeuse, exposing each of the plates to the star's light for less than one-hundredth of a second.

Fly's Eye. By astronomical standards, that is an extremely short exposure; in photographs taken through a large reflecting telescope, it produces a curious effect. Pockets of atmospheric turbulence along the telescope's line of sight tend to break up the incoming light. As a result, the telescope's big mirror is, in effect, divided into a number of smaller lenses, somewhat like multiple lenses in the eye of a fly. Thus the photographic plate records not one sharp stellar image but many--from 100 to 500 for each photograph. Only with prolonged exposure do the separate points merge into the single fuzzy spot familiar to astronomers.

But the Kitt Peak team decided to turn the "fly's eye" effect to its advantage. Keeping the exposures short froze the specks onto the plate before they were lost. Using that strategy gave the Kitt Peak astronomers much more information about the star than they could gather from a normal exposure. Each of the specks contains different information, like a peak or valley in the wavy sound track of a phonograph record; only when these bits of information are added together does the total information--in this case, a picture of a star--actually emerge. To analyze and combine the specks, the astronomers used a high-speed scanning beam that detected minute differences of light intensity as it swept each speck. The data from each of the 40 plates were then fed into a computer, which reassembled them into a single stellar image, like an artist piecing together a mosaic.

The computer-generated mosaic of Betelgeuse was only 2 1/2 in. in diameter, but detailed enough to show faint markings that the scientists think may be large hot spots in its atmosphere, perhaps gases erupting violently from the interior. Nothing on quite so dramatic a scale has been observed on the sun, which is in a more sedate stage of its evolution.

Many scientists consider such "speckle" photography to be one of the most important recent innovations in optical astronomy. When the technique has been refined, they believe, it will enable astronomers using earth-based telescopes to eliminate much of the obscuring effect of the atmosphere from their photographic plates.

Astronomers are already planning to use speckle photography to study the structure of other heavenly bodies. Some of their earliest targets will be quasars, which may well be the most distant objects ever seen by man, located at the very "edge" of the known universe. A more detailed view of these small, puzzling objects might help explain how they generate the prodigious amounts of energy that make their light visible as far away as earth.

* Proxima Centauri, which is 25 trillion miles away.

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