The thermosphere begins above the mesosphere at a height of about 80 kilometers. It has no well-defined upper limits like the other layers of the atmosphere. As a matter of fact it can be subdivided into two layers called the ionosphere and exosphere. The word atmosphere means “heat sphere” or “warm layer”. The temperature in this area is extremely high reaching over 2,000 degrees Celsius.
(A) The Ionosphere
The lower part of the thermosphere is referred to as the ionosphere. It extends from 80 kilometers to 550 kilometers above the earth’s surface. The actual size of the ionosphere depends upon the number of ultraviolet rays and x-rays given off by the sun on a given day.
The ionosphere contains oxygen, nitrogen oxide, and other gas particles which absorb the ultraviolet rays and x-rays from the sun. These particles then become electrically charged and are called ions. Ions are atoms that have either gained or lost electrons, the negatively charged parts of an atom.
The ions located within the ionosphere are important to radio communication. Radio waves bounce off the ions in the ionosphere and return to the earth’s surface thus allowing radio messages to be sent over great distances.
(B) The Exosphere
The upper region of the thermosphere is called the ionosphere. The exosphere is thousands of kilometers from the surface of the earth. Air within this region of the atmosphere is so thin that particles can travel great distances without hitting each other. Artificial satellites orbit the earth within this region. Satellites are important to people because they allow us to view events that occur all over the world through television, communicate through telephones and other types of technology, and take pictures of other planets, etc.