Cheryl Carrigan, age 12, of Utica, New York, for her question:

Are there really no sounds on the moon?

Astronomers told us and told us that our golden moon is a desolate place of eternal silence. Then at last our astronauts set foot on its surface. And they talked to each other. Their very words were relayed back to the earth    and we heard these sounds from the moon with our own ears. Surely the experts who said that there are no sounds on the moon must have been mistaken. Or so you would think. Actually they were correct.

The everyday sounds around us travel through the air to reach our ears. They are started by vibrating objects and use this energy to jog molecules and travel through the air. Sound waves can travel only through mediums made of molecules     such as solids, liquids and gases. If a telephone bell is sealed inside a vacuum from (which the air is removed, you can make the hammer hit the metal as usual. But the bell is silent     because there are no air molecules to carry the vibrations.

Sounds cannot travel through a vacuum. And the surface of the moon is just about as vacant as the best vacuums we can create on the earth. There is no lunar atmosphere. Even if there once was one, the moon would have lost it ages ago. The earth's massive gravity hugs our atmosphere and gas molecules must reach a speed of almost seven miles per second to escape it. The smaller moon is much less massive and its surface gravity is only one sixth of the earth's. Objects traveling at 1 1/2 miles per second can escape its pull. Gas molecules use heat to gain speed. In the hot lunar sunshine, they would gain enough speed energy to escape the moon's weak gravity.

The moon is silent because it has no atmosphere to carry sounds. But this does not explain why the lunar astronauts could chat with each other and relay their words back to our earthly ears. This mysterious happening should remind us of our radio and TV, which are carried through space on silent, invisible beams. Light, radio and other forms of electromagnetic energy do not need to travel through gaseous, liquid or solid mediums. They can whip through vacuums and other space. And they do so at the fantastic speed of 186,000 miles per second.

We use radio beams as carrier waves, modified with built in signals. They fan out from a broadcasting station, in silence. Some are trapped by antennas and led to receiving sets. There the signals that were added to the silent, invisible radio waves are sifted out and translated back into audible sounds and pictures.

There are no audible sounds on the moon. But the astronauts came prepared with ingenious equipment to generate radio beams and modify them with signals. These carrier waves crossed space and reached earth in a few seconds. Here ingenious receiving stations were waiting to trap them and translate their signals into sights and sounds from the lunar surface.