Karen Lerner, age 10, of Allentown., Penn., or her question:

Is the light year time or distance?

Our traffic signs read 45 m.p.h. 65 m.p.h. or whatever is the safe speed at which to travel. This m.p.h. is miles per hour, meaning a certain speed in which a certain number of miles would be traveled in one hour. Miles per hour is a unit for measurement of both time and distance, The light year is a unit of time and distances only on a very very grand scale.

The traveler here is light, the fastest traveler known. It whips along at an .averagc speed of 186,000 miles a second. At this speed it could whip around the earth s equator more than seven times in a second. In one year it travels about six million million miles. This unit, the light year, is very useful for measuring distances in the sky, We figure the distance of the star nearest our sun to be about 43 light years, roughly 26 million: million miles. The light which we see from it today set out towards us about 43 years ago.