Chelsea Donaldson, age 12, of Montreal, Quebec, Canada, for her question:

What does Stonehenge mean?

The word Stonehenge means "the hanging stones." This ancient name belongs to a circle of prehistoric stone pillars, some of them still crowned with enormous slabs that seem to hang up there in the sky. But the purpose of Stonehenge is far more amazing than its name. For countless centuries, the people of southern England revered it as a sacred relic of the forgotten past. Until very recently, its purpose and its history were shrouded in mystery.

Only one thing was known about it. On the day of the summer solstice, the morning sun rises at dead center over a certain stone. This clue suggested to modern astronomers that Stonehenge might be a prehistoric computer to chart the motions of other heavenly bodies. This proved to be true, though only part of the research is completed. We know that Stonehenge was built thousands of years ago. But as yet, no one can say who built it or how many celestial events the great circle of stones can compute.