Eric Wilton, age 13, of butte, Mont., for his question:
WHAT IS THE IONOSPHERE?
The ionosphere is part of the Earth's atmosphere that has many ions, or electrically charged atoms and groups of atoms, and free electrons. Cosmic rays and radiation from the sun produce these ions.
The layers of ionized air making up the ionosphere extend from about 30 miles above the surface of the Earth to the upper limits of the atmosphere.
The lowest ionized region of the ionosphere is called the v region, and it starts at an altitude of from 30 to 50 miles. The JJ region has an altitude of 55 to 90 miles while the F region starts at 9U miles anti goes up to about 190 miles.
The heights of these ionized layers or regions vary from day to night and with changes in solar radiation. The D region, for example, almost completely disappears at night. The other areas rise and become less strongly iodized at night because no solar radiation reaches the atmosphere.
The ionosphere actually makes long distance radio communication possible because it reflects certain radio waves many thousands of miles back to earth. At night, when the regions of the ionosphere go up, radio waves can be received even farther from the transmitter than during the day.
The ionosphere's ability to reflect radio waves goes down with an increase in radio wave frequency, and for very high frequencies is almost nonexistent. For this reason, long distant transmission of high frequency radio waves is limited to the line of sight. Both FM radio, or frequency modulation radio, and television use high frequency waves.
Long distant transmission can be accomplished only in a direct line, such as between the Earth and a satellite. The signal must then be relayed from the satellite to a distant point on Earth.
In the ionosphere the air is extremely thin and its density has about the same volume as the gas in a vacuum tube.
When the atmospheric particles in the ionosphere are ionized by ultraviolet radiation from the sun, they usually stay ionized because very few collisions occur between ions.
The B layer of the ionosphere is sometimes called the Heaviside layer or Kennelly Heaviside layer. It reflects radio waves of low frequency.
The F layer is sometimes called the Appleton layer, and it reflects higher frequency radio waves.
The F layer is further divided into as E' 1 layer, which starts at about 112 miles above the Earth, and an F 2 layer, which starts at about 186 feet from the surface. The F' layer rises during the night and therefore changes its reflecting characteristics.
An ion counter is the name of an instrument that detects X rays, gamma rays and nuclear particles. The best known type is called the Geiger counter, or the Geiger Muller counter.