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Beautiful, dancing lights in the sky have puzzled people for a long time. What causes the night sky to light up with moving streaks of color? These lights appear most often near the earth’s magnetic poles (you may know them as the north and south poles). In the north (the Arctic), they are called the aurora borealis or northern lights. In the south (Antarctica), they’re known as the aurora australis or southern lights.
The auroras are caused by the sun. Sunspots (cooler regions on the sun’s surface) cause solar storms. These storms send billions of tiny charged particles toward earth. But surrounding our planet is an invisible magnetic field that keeps these particles from entering our atmosphere.
Northern lights over the Arctic.
But the magnetic field lines come closest to earth near the magnetic poles. Many of the charged particles travel along these lines and enter our atmosphere at the poles. This allows these particles to react with the gas molecules high in our atmosphere. And the result is beautiful colors. These lights are normally visible only at high latitudes (near the magnetic poles), but very intense solar (sun) activity can drive auroras farther away.
The auroras can be different colors depending on what type of gas is reacting with the solar particles. Oxygen is green at low altitudes (60 miles above earth) or red at high altitudes (200 miles above earth). Nitrogen is blue or purple. The auroras can also be pink, violet, yellow, white, or orange, though these colors aren’t as common.
Northern lights over South Dakota.