||The English used in this article may not be easy for everybody to understand. (September 2011)|
The thermosphere is the layer of the earth's atmosphere directly above the mesosphere (middle layer) and directly below the exosphere (top layer). Within this layer, ultraviolet radiation causes ionization. That is why it is also called the Ionosphere. Shortwave radio wave can bounce off the Kennelly-Heaviside layer (ionosphere) and go to distant parts of the Earth.