text: The source of the auroras is the sun. The sun gives off high-energy charged particles (also called ions) that travel out into space at speeds of 200 to 440 miles per second. A "cloud" or gas of such ions and electrons is called a plasma. The stream of plasma coming from the sun is known as the solar wind. As the solar wind interacts with the fringes of the earth's magnetic field, the particles are "shocked" into flowing around the earth. Some of the particles are trapped by the earth's magnetic field. They follow the magnetic lines of force down to the ionosphere. The particles strike the gases in the ionosphere, causing them to glow, the same way electrons passing through the gases in a neon tube make a neon sign light up. The colors correspond to the different gases in the ionosphere. Oxygen atoms give off red and green light, depending on how high they are in the ionosphere. Nitrogen molecules give off blue and violet light.