ionosphere
Original archive entry. The text, images and links below are kept as they were written.
Region of ionized gases surrounding the Earth and extending from about 60 km (33 naut. mi) to distances up to several hundred kilometers. The ionization in this region is due to bombardment by ultraviolet radiation and X-rays from the Sun, and by cosmic rays. The existence of this region makes possible long range radio communications through reflection of terrestrial radio transmission.