If you’ve ever seen the aurora borealis, you know what a spectacular sight it can be. You also know it’s all about location, location, location. The northern lights are generally only visible in the more northern latitudes, but this week, many people were seeing these amazing displays as far south as Georgia and Alabama. Why was this aurora event visible to so many?
The chain of events that caused the lights started as early as 9:36 p.m. on Friday, with the occurrence of a Coronal Mass Ejection. These CMEs are large eruptions of positively charged ions and negatively charged electrons from the sun that travel through space, sometimes heading toward the Earth. They can occur at any time, but typically, these events are more common during periods of high solar activity. From now until 2013, there will be a solar maximum, or a peak in solar activity, meaning we will likely see more events like these CMEs, as well as sunspots and solar flares.
The current CME occurred on the side of the sun facing the Earth, sending a lot of emitted particles in our direction and causing a geomagnetic storm. A geomagnetic storm is a disruption of the Earth’s magnetic field that occurs when something like a CME hits it, and depending how strong the storm is, it can affect the amount of disruption we see here on Earth. This particular storm was moderate, rated a G2 on a scale of 1-5, with a G5 rating being the strongest. A G5 storm, the greatest threat to our communications network, could cause days of GPS satellite disruption and radio signal loss, while other effects could include widespread power outages and damage to transformers. Intense auroras would also be possible and might be visible as far south as Texas and Florida. I wouldn’t mind seeing a few more auroras, but I’d be lost without my GPS - really!
So what actually happens when these CMEs approach the Earth, and why was this aurora so awesome? The sun is always emitting charged particles, and these particles, coupled with the sun’s magnetic field, compose the solar wind. This solar wind is always present, blowing out in all directions from the sun. The illuminated side of the Earth is where the solar wind hits, and that causes a constant bend in the Earth’s magnetic field lines. When something like a CME is emitted from the sun, that ultimately means the solar wind becomes stronger and results in a more drastic compression, or bending, of the Earth’s magnetic field.
As the Earth’s magnetic field lines bend farther backward around the Earth, magnetic reconnection events occur and force electrons streaming toward the poles and into the ionosphere, which is the upper portion of Earth’s atmosphere, containing various elements like oxygen and nitrogen. When these atoms are struck by that surging stream of electrons, they become "excited" and give off light.
The type of atom struck and the altitude at which it is struck dictates what color of northern lights you will see. Blue light is emitted when nitrogen is struck up to 60 miles in altitude, purple/violet light for nitrogen above 60 miles, green (most common) for oxygen up to 150 miles in altitude, and red for oxygen above 150 miles in altitude.
Auroras are not typically seen as far south as the one Monday night, but the timing was perfect for us to be able to see that one: It occurred mostly after dark across the U.S., and clearer skies prevailed over many areas. This time, there was enough energy to give us a spectacular showing, and it certainly made for some great photos and videos from our dedicated iReporters.
Keep your eyes open for the next solar event, because we are sure to have a few more chances over the next year or two to see these beautiful displays of Mother Nature. At least maybe next time, I won’t go to bed so early.