Rand McCarthy, age 8, of Tucson, Ariz., for his question:

WHAT IS AN ATOM MADE OF?

A tiny atom is much too small for our eyes to see. Yet clever scientists found other ways to figure out what is inside it. They learned that the tiny atom is made of even tinier pieces called particles. Naturally they have names for these different particles. Some are called electrons, some are protons and some are neutrons. There also are many other atomic particles with even fancier names.

Scientists also discovered something even more amazing. These different particles are not just jumbled together inside the tiny atom.    

They are arranged very neatly in working order. Most of them are packed in a tight little fist called the nucleus, and it is in the middle of the atom. The particles called electrons swing around the nucleus, somewhat as the planets swing around the sun.