Deborah Kubiak, age 9, of Portage, Indiana, for her question:

Why can't the astronauts hear sounds on the moon?

Sounds can travel through air, through solid steel and under water. But they cannot go through empty space. The everyday sounds we hear can travel through the air because the air molecules help to jog them on their way. They travel faster through water because the helpful water molecules are closer together than gaseous air molecules. And sounds travel even faster through the crowded molecules of solid steel. The moon has no air, no gaseous molecules to jog sounds on their way.

This is why ordinary sounds on the moon get nowhere at all. You could holler or bang a drum    but nobody would hear you. But this problem did not bother the astronauts. They came prepared with supplies of their own air to breathe. They also had radio sets. And radio waves are very different from ordinary sound waves. They travel much, much faster and they can travel through empty space. The astronauts used radios to talk with each other and also to talk with the people on earth, almost 240,000 miles away.