Philip Calvin, age 9, of Charlotte, N.C., for his question:

What exactly is a light year?

Sometimes a bright star looks so close that you think you could climb a tall ladder and touch it. Others look farther away. Actually, the closest star is far, far away and the distance between it and the other stars is enormous. Here on the earth, we use miles to measure distances from here to there. But a million miles is almost no distance at all in the enormous sky. This is why the light year was invented. It measures a distance that equals almost six million million miles.

The speedometer on a car tells how many miles per hour we are going. When it says 25, it means that we are speeding along at 25 miles an hour. A light year tells how far light travels in one year. The speed of light is always the same so in one year it always travels the same distance. The nearest star to our sun is about 4 1/2 light years away    which is almost 27 million million miles.