Cathy Jean Hix, age 11, of Red Boiling Springs, Tennessee, for her question:

How many earth miles are in one light year?

This measuring job took many many years and it is only as accurate as human beings can make it. It will be done again and again in the future and each time the figure will be perhaps a hair's breadth closer to the exact truth. It is, as we all know, the distance a beam of light travels in one earth year    which is 365 1/4 earth days. In round figures, the speed of light is 186,000 miles per second. When this number is multiplied by the number of seconds in one earth year, we get the number of miles in the light year.

This big number is close to six million million miles. We can be somewhat more exact and say that it is 5,880 thousand million miles    which is 5,880 followed by nine zeros. So far as we know, nothing in the universe travels faster than light. But radio and other forms of electromagnetic energy equal its speed. Certain subatomic particles are also thought to whiz through the universe at the fantastic speed of almost six million million earth miles per year.