What is the Aurora Borealis? (And Happy Autumnal Equinox!)

Today I hopped onto NatGeo and came across these beautiful photos of northern lights taken in Norway. I immediately realized I had absolutely no idea what the northern lights really are, or how they’re formed. When you think about it, the sun is the only natural cause of light (besides fire anyway), so how do these phantasmal strips of color form, and why do they undulate across an otherwise dark nighttime sky? Since it’s just recently the Autumnal Equinox, let’s celebrate by learning about a little solar activity!

As it turns out, this magical phenomenon is also caused by the sun. Now, bear with me; I’m not an astronomer and I have a decidedly difficult time understanding astronomical topics, but I’m going to give it a shot anyway.
So there’s the sun and then there’s Earth. Earth has these crazy magnetic fields around it. I’m sure there’s a scientific explanation for this, but trying to understand the auroras took it out of me and for now, I’m going to stick with magic being the answer. Magic, and something to do with iron. So, the earth has these magical magnetic fields around it.
Then there’s the sun. And, apparently, wind comes off the sun’s corona, or outermost layer, but it’s not exactly wind. In fact, it’s plasma. I had no idea, but plasma is actually the fourth state of matter (the others being gas, liquid, and solid). So, I say to myself, what the hell is plasma if it’s not one of the three things I understand to be matter? Plasma, as in solar wind plasma, is what happens when a gas gets so hot that its electrons say ‘peace out!’ and evacuate. So solar wind is essentially a crapload of electrons and protons floating around in space. In fact, a lot of space is made up of plasma because stars are so incredibly hot that their electrons pack up their personals and head out on their own. What does that look like? Well, that’s tougher; it’s kind of like glowing light and gas mixed into one.
Do you remember these fun-for-the-first-ten-minutes toys from your childhood?
They’re called “plasma lamps,” and although it’s not exactly solar wind, it gives you an idea of what solar wind might look like (for those of you that really just can’t understand something astronomical without a visual reference…like me). Kind of. A little. Anyway.
Windows to the Universe says that the Sun is flinging 1 million tons of this stuff into space every second, but that the plasma is so thin near the Earth that it wouldn’t even ruffle your hair. (My brain can’t wrap around that plasma isn’t goopy, however, and that if solar wind ‘ruffled your hair,’ it would probably set you on fire at the same time.)
So, this solar wind comes off the sun and hits those magnetic fields I was telling you about earlier. You’ll notice that the magnetic fields East and West stick out pretty far, whereas dead center North and South, there’s not a whole lot going on. It turns out those little renegade electrons and protons only get funneled down towards the Earth’s poles. Notice the path of the flowing blue lines in this image:
So the “Nothern Lights” (Aurora Borealis) are seen near the Arctic Circle and the “Southern Lights” (Aurora Australis) are seen in the South Pacific/Antarctica. Usually the auroras occur between 60°-75° latitude, forming two “auroral ovals,” one over each end of the planet. The ovals can expand somewhat during high solar activity.
So anyway, those plasma-partying protons and electrons bump into the stuff that makes up our atmosphere – mostly oxygen and nitrogen atoms – and that’s what causes the big commotion. When the plasma particles collide with our atmospheric elements, there’s about a gajillion little bursts of light that result. These bursts of light make up the auroras, and the color of the aurora is dependent upon which element the plasma is bumping up against. The auroras shimmy and swim because those magnetic lines we talked about earlier get stretched and “broken,” and it makes the auroras look like they’re undulating when the lines “reconnect” or stretch back.
The image above shows the color spectrum of auroras. Basically, solar wind is only colliding with oxygen and nitrogen, because those are the most prevalent elements that high up in our atmosphere. So the properties of the gas itself, the energy with which the collision happens, and the altitude at which it takes place all contribute to the color you perceive. (Click on the image or here to go to WebExhibits, where there’s even more cool info about auroral colors!).
That about ends my mental ability to maintain consciousness on this topic, so let’s recap: The sun breaks wind and when it gets to Earth, there’s a magical display of dancing color!
SCIENCE IS AWESOME!!


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More?

The Exploratorium is one of my new favorite sites. I LOVE online museums! Click the link for their page on auroras.
You can also visit The Exploratorium to see the current activity of the sun.
Check out this righteously awesome photo slideshow from NatGeo of auroras.
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Posted on September 23, 2010, in Earth & Sky and tagged , , , , , , , , , , , , , . Bookmark the permalink. 5 Comments.

  1. I apologize in advance for the poor spacing in this article – WordPress for some reason is not respecting my choice in spacing paragraphs and photos! Rude.

    :)

  2. Very nice explanation. The Geophysical Institute’s Aurora Forecast (http://www.gedds.alaska.edu/auroraforecast) and NOAA’s Auroral Activity (http://www.swpc.noaa.gov/pmap/index.html) are two of my favorite websites about auroras. They help you find out when viewing is best in your area.

    Sorry if this posted more than once. I’m having WordPress issues also.

  3. whooosh! you have made this topic so easy to understand!

  4. Your picture with the solar wind and the earth’s magnetosphere is wrong. The solar wind does NOT flow to earth’s atmosphere along the magnetic field lines at the poles.
    The particles causing the aurora come from the Van-Allen radiation belt, where particles are trapped in a so called magnetic bottle. These particles are accelerated and move along the field lines towards the poles when the solar wind causes magnetic reconnection in the tail of the magnetosphere.

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