Elizabeth Iocco, age ll, of Long Island City, N.Y.., for her question:

What is a radio telescope?

An ordinary telescope has lenses to gather light from distant stars. A radio telescope has antennas to gather radio waves from stars and other objects in the heavens. Both light and radio are forms of the electromagnetic energy that pours forth from the sun and its starry sisters. All such forms of energy travel at about l86,000 miles a second. But they pulse along on different frequencies,, and radio frequencies are at least a million times slower than the frequencies of light.

A radio telescope catches radio waves in a huge bowl of antennas and focuses them onto other antennas. Radio receivers pick than up as electrical impulses. The impulses are then changed into wavy lines and recorded on paper. To an expert, this ragged writing can describe a star that is too far away to be spotted by the probing lenses of an ordinary telescope.