Bill Thomas, age 10, of Lansing, Michigan, for his question:

Why doesn't the sky end?

When a young space alter looks up at the sky he knows that he is gazing out through the faraway reaches of space. He also knows that every day the earth spins around and every hour the sky brings him a changing view of the heavens. He also knows that every year the earth rolls in a wide orbit around the sun. It changes its place in the sky and the changing seasons show different things in the sky, different view of the vast reaches of outer space. These changes repeat and repeat in daily and yearly cycles of circles. But the heavenly parade never ends. There seems to be no end at all to the sky above.

Sooner or later, every young space alter wonders about this question. And even the best brains in the world cannot answer it. Super telescopes and radiotelescopes have probed zillions of miles in all directions, far, far beyond what our eyes can see. But they have found no end to the sky. Wherever you stand on the round globe, the endless sky reaches from horizon to horizon. What's more, if the spacious sky did have an end, we humans would ask what is on the other side. Perhaps the human brain could not imagine the end of outer space but at present we do not know whether it ever ends.