Joanne Holetz, age 11, of Bethlehem,Pennsylvania, for her question:

How long is a light year?

The light year uses time to measure distance. This is no mystery, because we use the same trick when we talk about traveling at so many miles per hour. The only difference is that the light year does this in a very big way. The speed gauge it uses is the velocity of light    which is 186,000 miles per second. Sunbeams, moonbeams and light from the stars all whisk around the universe at a steady speed of about 669,600,000 miles per hour.

At this speed, it takes the sun's light about eight minutes to reach the earth. However, light from the stars takes years, even hundreds or thousands of years to reach us. The light year was invented to measure their distances across the vast reaches of space. It equals almost six million million earth miles    which is the distance a beam of light travels in one earth year. In round figures, the mileage is six trillion, or six plus a string of 12 zeros.