Recently, I was asked via e-mail about the Aurora Borealis. Since temperatures around here have been record-breaking hot, I figured an article on a great Northern phenomenon such as this would be an excellent distraction from the heat!
I'd like to start off by admitting that I've never actually seen the Northern Lights with my own two eyes. Living at 41* N latitude means that I am generally, but not entirely out of range for this light show. Occasionally, we will hear about the possibility of seeing an Aurora, but thanks to Ohio weather, we're usually clouded over! Regardless, millions of images are available from sources ranging from professional photographers, to hobbyist websites and blogs. The image seen at top right was captured by Senior Airman Joshua Strang of the USAF.
So what exactly causes the Aurora Borealis? The answer, my friend, is blowing in the wind... The solar wind, that is! Our star, the Sun, is constantly bombarding us with charged particles. These charged particles are mostly electrons. Along with these charged particles come other scary things such as x-rays and radiation. Thankfully, the Earth has a defense system, known as the magnetosphere. The magnetosphere is comprised of the magnetic field surrounding our planet, and is very similar to the lines seen in iron fillings around a magnet. Because the solar wind particles are charged, they are strongly deflected by the magnetosphere.
So what does this have to do with the Aurora, you ask? As you can see in the illustration above, there are two holes in the magnetosphere, which are approximately funnel-shaped. These holes are not our doing, but rather, naturally occurring. Solar particles are funneled into these holes at great speed. Since these particles are highly energetic, when they collide with atmospheric particles, they release small bits of light. Introduce enough of these particles into Earth's atmosphere, and a visible Aurora Borealis occurs. Aurora Borealis can come in many shapes and colors. Different atmospheric gases cause different colors; oxygen causes green and red auroras, and nitrogen causes mostly blue and violet colors. The image at right illustrates this process well, and shows the altitude at which this phenomenon occurs (Image Courtesy of NASA).
Of course, this phenomenon also occurs in the Southern hemisphere, where it is known as the Aurora Australis. The Aurora Australis is less widely known, however, as less people inhabit the far Southern polar region than the Northern polar region.
Maybe some day I'll get to see them yet!
For more details on recent discoveries, check out The Aurora Borealis, Part II.