Radio Eye

Astronomers are not building many ordinary optical telescopes these days, but electronic telescopes for catching radio waves from space are under construction in many countries. One of their advantages: they need not be built on clear-aired deserts or mountaintops. They can see the sky through the thickest clouds or even the smoky glare of Pittsburgh or Los Angeles.

Last week, in cloudy New England, Harvard University dedicated a new radio telescope at the Agassiz Station of the Harvard Observatory, 25 miles west of Cambridge. The telescope's 60-ft. "dish" antenna is steerable (it points anywhere) and is specially designed to pick up 21-cm. radio waves from the great clouds of hydrogen that clutter the universe.

The 21-cm. waves were first observed at Harvard five years ago by Drs. Harold I. Ewen and Edward M. Purcell, and they have proved wonderfully useful in showing up features of the universe invisible to telescopes using light. The hydrogen clouds are everywhere, streaming along the spiral arms of the galaxy, clustered thickly in the Milky Way. An average cloud may be 25 light years (150 trillion miles) in diameter and weigh 100 times as much as the sun.

If the hydrogen clouds are moving, as they generally are, the radio waves that come from them are slightly longer or shorter than the standard 21 cm. This difference allows radio astronomers to measure the speed of the clouds. It also allows them to "see through" a cloud that is hiding more interesting clouds. All they have to do is to set their detecting apparatus to ignore the waves from the obscuring cloud and tune in the waves from the clouds behind it. Harvard's new telescope will be particularly adapted to this selecting process. It will also have sharper vision than the 24-ft. "dish" that has been doing Harvard's radio astronomy. If the moon were a source of 21-cm. waves, the 24-ft. telescope could not distinguish it from two other moons ranged in a line beside it. All three would share the same blur.

The improved resolution of the 60-ft. telescope would let it see the three moons separately. When it starts to map the sky, the hydrogen clouds, which are now known only as broad blurs, will show much more detail. More knowledge of the hydrogen clouds will give astronomers a better understanding of the primeval gas that is the basic stuff of the universe.

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