Greg Russell, ago 11, of Sac City, Iowa, for his question:

How high is the ionosphere?

The ionosphere is a layer of thin atmosphere far above our heads. It begins where the stratosphere ends, about 50 miles above the ground. It is arranged in three distinct shells, reaching up about 650 miles.

This layer of atmosphere is very important to us. Without it we would. have no radio or TV networks. For the beams which carry these electromagnetic waves travel in straight lines. They cannot bend around the earth. The ionosphere acts as n mirror and reflects them back. They strike the ionosphere at an angle and reflect beck at an angle. Hence they reach the earth far from their broadcasting station.