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Folklore is rich with explanations for the stunning night-sky lights, the aurora borealis. Various cultures have explained them as dancing spirits or blood raining from the clouds. Aurora was the Roman goddess of the dawn. Boreal is a Latin word, meaning "north." Thus, the northern lights. In the Antarctic, the lights are called the aurora australialis, or southern lights.
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.
The northern lights are always moving, like giant curtains of light weaving and swaying across the sky. This is caused by the constantly changing interaction between the solar wind and the earth's magnetic field. It is not unusual for the solar wind to generate 100,000 megawatts of electricity in a three-hour auroral display. This can cause temporary interference with power lines, radio and television broadcasts, and satellite-to-earth communications. By studying the auroras, scientists can learn more about the solar wind and how it affects the earth's atmosphere.
Click here for pictures taken north of Wasilla Alaska on October 14, 1999.
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