Teresa Cavander, age 12, of Dunbar, West Virginia, for her question:

How long must light travel from the nearest star?

Strictly speaking, of course, our sun is as starry as any star in the heavens. But as a rule we do not count it when we think of star distances. If we did, we would say that it is merely light minutes away. Each sunbeam takes about eight minutes to travel the 93 million miles from the surface of the sun  to the earth.

Let's discount our starry sun and think of the stars that shine after it sets. On a clear night, some of them look almost close enough for a tall person to reach up and touch. But of course they are vast distances away. And what we see is their light which has traveled across vast reaches of space. The average speed of light is 186,000 miles per second, which means that starlight travels more than 6,669 million miles each and every hour. Clocking distance and travel time is no surprise to us. We do it with a car speedometer that reports how many miles we are traveling per hour.

However, this speed in terms of miles per hour is much too puny to figure the distance of the stars. Astronomers use several whopping units for measuring the immensity of celestial distance. One is the light year, the distance that light travels in one earth year. This distance is roughly six million million earth miles    which is figure six plus twelve zeros. The light year is just fine for measuring the distances of the nearest stars    that is, those nearest to our starry sun.

The famous star Alpha Centauri shines bright in the skies below the equator, quite near to the South Cross. Sometimes it can be seen as far north as Florida and southern Texas. Actually, Alpha Centauri is a double star though you need a telescope to show that it is really two close stars orbiting around each other. For a long time, Alpha Centauri was rated as the sun's nearest neighbor. It is at a distance of 4.4 light¬years. This means its twinkling light that reaches the earth set forth towards us about four years and five months ago. Some years ago, astronomers discovered that this star is really triplets. A small red dwarf star is orbiting the bright twins in the center. As it orbits around, it changes positions in relation to the earth. At present it happens to be closer to us than Alpha Centauri. It was named Proxima, the near one, but it is too small to be seen without a telescope. Its light is captured on telescopic plates. And this light traveled a little less than 4.4 years before it arrived on earth to take it"1wn photograph.

Light from most stars travels hundreds of years and sometimes thousands of years to reach the earth. This means that their twinkling beams started forth a long, long time ago. And what we see are the stars as they then were. If, in the meantime, the stars change, we must wait for light to bring us the news.

Many stars are 300 light years away    a moderate celestial distance of 300 times six million million earth miles. Suppose one of them exploded this afternoon and became a dazzling nova. We would not see the dramatic event from the earth until the year 2269. Our brightest star is Sirius. When we see it in the winter sky we are seeing it as it was 8.6 years ago. Its light, traveling at 186,000 miles per second, takes more than eight and a half years to reach us.