One dark, cold evening you step outside into a strange world. Instead of a million stars overhead, the sky is pulsating in green and white waves of light. Soon there are pinks, purples, and blood red hues. Is there a huge alien spaceship beyond the horizon casting this eerie glow? No, you are looking at the aurora borealis, the Northern Lights. (That is unless you live in the southern hemisphere, in which case you are looking at the aurora australis, the Southern Lights). Actually, there might be just a wisp of green light waving in one small part of the sky or there might be tall columns of purples and pinks that seem to cover most of the sky. Auroras can be different colors, different intensities, and different shapes. But where do they come from and what causes them?
Our story begins about 93 million miles away from Earth at the sun! The sun is an active star, a very hot ball of gas. Eruptions from the sun send energy particles, called electrons and protons, out into the solar system as part of the solar wind. The solar wind travels at about a million miles per hour. Within a few days it reaches Earth. This may sound scary, but it is not, because the earth has a magnetic field that acts like a shield. Known as the magnetosphere, this field extends out from the north and south poles to form a protective layer. When the energy particles from the sun hit the field, they travel along the magnetic field lines to the poles where they enter the earth's upper atmosphere. When these energy particles collide with particles in the air, such as oxygen and nitrogen, they create the lights we see as auroras.
The northern lights are most commonly seen in the latitudes nearest the North Pole. They are rarely seen in the lower latitudes in places such as Florida. Auroras are more likely to occur during autumn and spring. An increase in solar activity increases the likelihood of auroras on Earth. Solar flares are huge explosions on the sun. Scientists don't know why increased auroral activity coincides with our seasons, they are studying it. However, it's very handy to know that we can predict increased auroral activity by keeping track of solar flare activity.
Check the bulletins on my topic page. I will let you know when we are likely to see auroras so that you can keep a close eye on the sky for those eerie yet beautiful lights.
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