The Northern and Southern Lights, collectively known as Aurora Polaris, are caused by the activity of the sun. The lights vary in intensity, duration, and extent and are visible in high latitudes during solar storms. The colors indicate the altitude of the reaction.
The northern lights, or aurora borealis, are bright bands, circles and streams of colored light that sometimes appear in northern latitudes. The Southern Hemisphere has similar light shows called Aurora Australis or Southern Lights. Both the northern and southern lights are collectively referred to as the Aurora Polaris. Lights can span the visible, infrared and ultraviolet spectrum and vary in intensity, duration and extent. They can last a few minutes or all night; The Northern Lights can also occur during the day, but sunlight makes them invisible.
The Northern Lights are caused by the activity of the sun. Strong magnetic activity occurs continuously on the surface of the sun, and electrons and ions are constantly being ejected into space. This “plasma”, called the solar wind, is ejected in all directions. It is only when a strong solar wind blows in our direction that the Northern Lights occur.
Since electrons and ions are charged particles, they are affected by the earth’s magnetic field, which sweeps them apart as they approach and funnels them towards both poles. The particles spiral along the “cone” of the magnetic field until they reach the atmosphere, where they interact with atmospheric gases to cause lights in the sky.
The stronger the “storm” gets on the sun’s surface, the more particles are ejected into space and potentially into our atmosphere. The more particles, the further south the particles reach before being consumed in a reaction with atmospheric gases. Auroras are visible in the Arctic and Antarctic at night whenever there are solar storms and are regularly seen in northern countries with high latitudes. The further south you go, the less likely you are to see the Northern Lights, with the air show visible at the equator only once every century or two.
The colors of the aurora borealis are indicative of how high up in the atmosphere the reaction is taking place. Red lights indicate particles that react at higher altitudes than green, for example. Since the solar wind always bathes the earth in particles, some upper atmospheric reaction always takes place. It’s only when the solar wind is particularly strong that the reaction is bright enough to be seen with the naked eye.
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