Aubrey Metcalf, Jr., age 10, of Tulsa, Oklahoma, for his question:

How thick is the world between the North and South Poles?

The earth is a big ball. And one way to measure a ball is with a line straight though the very middle from side to side. This is called the diameter and it is a very sensible way to measure the size of the earth. For one thing, you find out that the diameter between the poles is a little shorter than the diameter through the equator. This tells us that our dizzy old planet bulges a bit around the waist, which is the equator.

The earth's diameter between the North and South Poles is about 7,899.83 miles. The diameter at the equator is 7,926.41 miles. If you don't want to use the word diameter, you can say that the thickness of the earth between the poles is just a few paces short of 7,900 miles. And at the equator, our earth is about 26 1/2 miles thicker than it is through the poles.