Tammy Busher, age 8, of Wichita, Kansas, for her question:

How far is it to the center of the earth?

Our earth is a great big globe and we live outside on the surface. Wherever we live, the center is the same spot, straight down under our feet. In most places, the distance from here to there is about 3,956 miles    plus perhaps a half a mile. The figures are not perfect because the earth is not a perfectly round globe. It bulges a bit around the equator. The North and South Hemispheres may not be exactly the same size or shape. So the distance to the center depends upon where we happen to be standing.

If we stand on the equator, the distance to the center is about 3,963 miles. Suppose the two hemispheres are exactly alike. Then the north pole and the south pole are the same distance from the center. This distance would be about 3,950 miles. It is, very, very difficult to measure the exact size and shape of the earth. If scientists find a better way to do it, our present figures may gain or lose a mile or so.