Northern Lights, Explained

Northern Lights, Explained

England, Mike
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If you've never seen the northern lights – and almost 95% of Earth's population hasn't – this year may be your best chance. Massive surges of solar activity are blasting Earth with more magnetic energy than it's felt in 20 years. This means that aurora borealis will be bigger, more vibrant, and visible much farther south than normal. Montana has already hosted a few breathtaking atmospheric lightshows this year, and if things go as expected, there's much more to come.

“We're riding the peak of an eleven-year solar cycle," says Dave Klumpar, a reasearch professor of physics and head of the Space Science & Engineering Lab at MSU-Bozeman. "There's an enormous amount of electrical activity on the sun right now. Thousands of tons of solar material are being ejected into the solar system, and that part of it that is directed at Earth can have spectacular consequences."

This huge "solar burp," as Klumpar calls it, starts with sunspots, which are magnetized regions of relatively cool gas. These gasses multiply and collide with areas of opposite polarity, causing intense, volcano-like solar flares and coronal mass ejections (CMEs). Many are over ten times the size of Earth. Enormous quantities of solar material, mainly ions and electrons, from these CMEs bombard Earth's magnetosphere, which is the region around Earth controlled by a strong magnetic field. This bombardment causes a violent electrical disturbance.

"When the conditions are just right, as they often are," explains Klumpar, "this disturbance accelerates the solar particles, driving them through the magnetosphere and ultimately funneling them along Earth's magnetic field into the atmosphere."

That's when the light show begins. Speeding electrons collide with atmospheric nitrogen and oxygen atoms, exciting them and upsetting their natural state of neutrality. This "ionizes" the atoms, sending them into an electromagnetic frenzy. Eventually, the energy escapes and the atoms return to their normal state. "When that introduced energy is released," Klumpar explains, "it comes out as light."

The light can take many forms, from wavy greenish plumes to burnished red sheets that blanket half the night sky. The most common effect in Montana is the white or light green streaks known as "curtains." Several variables control aurora colors and patterns: type of ionized atom, intensity of collision, and angle of observation, to name a few. The only constant is the spectacular and mesmerizing effect. "The first big one we saw in Bozeman this year was in the spring," remembers Klumpar. "It was cloudy all day, but around midnight the sky cleared and the aurora came into view. Light was streaking across the sky like a celestial firestorm. I stayed up, watching, until four in the morning. It was incredible."

For more information about auroras, solar activity, or any other related questions, visit www.spaceweather.com or www.sec.noaa.gov. For free auroral alerts via e-mail, go to www.skypub.com/news/astroalert/astroalert.html.
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