Twinkling Mysteries

To most laymen, the atmosphere on a clear day or night looks beautifully transparent. The astronomers, aware of this illusion, know that even the clearest atmosphere is opaque to many kinds of radiation. Visible light pushes through it without much loss. So do ultraviolet and infrared if their wave lengths are not very different from ordinary visible light. Most other radiation coming from outside the atmosphere is absorbed before it reaches the ground. The chief exception is radio waves, which penetrate not only the atmosphere but also thick clouds.

British astronomers, often frustrated by the persistent clouds over their murky island, have taken advantage of this "radio window" and are busily developing the brand-new science of radio astronomy. Their "telescopes" are powerful radio receivers with antennas designed to respond to signals from one direction only. With the directional receivers, they sweep the sky, looking for natural broadcasting stations in space.

There is plenty to look for. The sun sends out radio "noise," but not very much of it, considering its size and nearness (93 million miles). Far more interesting are a number of mysterious "point sources" scattered around the sky. More than 30 have been found so far. They do not correspond to any object that shines with visible light. They appear to be very distant and perhaps as big as stars. They must be peculiar stars, however, for apparently they send out 100 million times as much radio energy as the sun.

Like stars, the point sources twinkle--in the radio sense. Two identical receivers a short distance apart do not pick them up with equal brilliance. The "twinkle" is supposed to be due to electron clouds in space that deflect the radio waves.

No one knows for certain yet what the mysterious objects are made of or exactly how they send out their energy. But Britain's radio astronomers, delighted with their fogproof window on the universe, are rapidly improving their instruments and trying to find out.

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