Auroras, what are they?

Thursday, September 8th, 2005 at 11:23 AM by Dave

What causes an aurora (otherwise known as "the Northern Lights")? Auroras originate in the active regions on the Sun’s surface where sunspots form. Sometimes these active regions give off violent discharges of particles (called coronal mass ejections). These charged particles leave the sunspots and go outward into space. When these charged particles interact with the Earth, we get auroras.^[1]

What happens when the charged particles hit the upper atmosphere of the Earth? These particles strike the outer electrons of the gases that surround the Earth (mostly nitrogen and oxygen). These electrons absorb the additional energy from these particles and go to a higher orbit surrounding the atom’s nucleus. This higher orbit is not stable and the electron moves back down to its original (stable) orbit around the nucleus. When it does so, it gives off a particle of light (called a "photon"). Now repeat this one interaction by literally trillions of particles hitting trillions of gas atoms and add in the effect of the Earth’s magnetic field deflecting the solar particles into the northern (and southern) polar regions of the Earth, and you have the explanation for the wavering bands of light we call the aurora.

In yesterday’s article by Juan, you noticed that the Sun gave off a major solar flare. This flare is thought to come from the same sunspot region which gave us some beautiful aurora displays in August. During the next few weeks, as this major sunspot region rotates around the Sun to face the Earth more directly, we can expect to get major auroral displays. You can stay posted on the Current Central Minnesota Aurora Probability by looking at the Solar Activity Panel on the right hand side of this page.

Clear Skies to all!

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