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Aurora mystery solved!

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By News9 Meteorologist Carrie Rose

NASA released information Thursday (July 24, 2008) about a major discovery in the study of Earth's aurora borealis and aurora australis.  Scientists have finally discovered (and have the evidence to prove it!) what causes the mysterious and graceful Northern and Southern Lights phenomena. 

Many of you may have been taught in your Earth Science class that the aurora is caused by the Sun emitting charged particles that interact with our magnetic field at the poles.  While this is true, no one knew exactly how the process worked, especially for the brightest aurora events.  So NASA decided it was high time to figure out what causes this elusive dance of light.

In February of 2007, NASA launched five satellites collectively called "THEMIS" for Time History of Events and Macroscale Interactions during Substorms.  Woah, okay...that's quite a name, buddy!  There were also 20 ground observatories utilized in Canada and Alaska. 

The satellites gathered data for a year, until a solar wind storm (that's when the Sun suddenly sends a burst of electrically charged particles toward Earth...basically it's a lot of magnetic energy speeding toward the Earth's magnetospehre) gave the scientists a major break. 

On Februray 26, 2008, the THEMIS satellites observed a major solar wind storm distorting our magnetosphere (the magnetic field surrounding and shielding the Earth) and stretching it like a rubber band until there was a connection on the other side of the Earth of the field lines (see diagram).  That connection is like when you snap a rubber band at its breaking point, and there is a shock wave sent back from the connection point.  When the magnetic field was bent around the Earth and connected on the other side, that connection caused a huge "explosion" of magnetic energy to be sent back toward Earth.  When these charged particles were sent flying back to Earth, they interacted with our magnetic field around the poles, and made a big aurora event!  (Read about that aurora event here). 

Of course, you can still get aurora events from that initial solar wind, but it's the biggest and brightest ones that are caused by these "substorms," when the connection of magnetic field lines shoots charged particles back at Earth.  Check out photos of the substorm aurora event here.

That connection, or "substorm" location, is only about 80,000 miles away from Earth, or about a third of the distance from the Earth to the Moon.  This research confirms for the first time that "magnetic reconnection" is the cause of the best aurora events.

This makes me want to go to Alaska in the winter to catch some aurora borealis!

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