David Barry, age 11, of Somerville, Massachusetts, for his question:

How can a compass help you at the equator?

The first compass was a magnet and so is the first compass a young science student is likely to own. The moving tip of the magnetic needle points to the earth's magnetic pole, which is near the North Pole of the globe. Its pointing finger shows the north direction. And when you know which is north, you can figure out the other directions. Facing north, east is on your left and west on your right. South is behind you and though you may not know it, the same compass needle is pointing right toward it. That long needle has two ends. The free end points directly north    so the other end must point toward the opposite direction    which is south.

A magnetic compass knows just where the north and south directions are. But it does not know a thing about the equator    which is a man made line around the world's waist exactly halfway between the North and South Poles. North is north and south is south wherever you go, this side or that side of the equator or right on it. A compass magnet does not swerve at the equator so it is just as helpful there as it is anywhere else on the globe.