Dan Kurpis, age 9, of St. Paul, Minnesota, for his question:

How bits can a star be?

It is hard to imagine the size of the planet Earth, which is our whole world. But the size of a star is enough to strain your brain. So get ready to stretch stretch stretch your imagination. For instance, let's suppose that our starry sun were hollow    which of course it is not. If it were hollow, it could swallow more than a million earth¬sized planets    and still have room for more. Compared with the earth, our sun is a whopper. But compared with other stars, the size of our sun is merely medium.

There are about 200 billion, billion stars in the Universe. And naturally our astronomers have measured only a very few of them. Most of these are about the same size as our sun, perhaps a little bit larger or smaller. The smallest stars are smaller than the earth. The largest ones we know about are at least 1,000 times wider than the sun. Let's suppose one of them changed places with our sun    which of course is impossible. But if this could happen, the giant star would fill the inside of the Solar System and spread far out beyond the earth's orbit.