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Stauchy Blog » Blog Archive » Auroras - Mon. Oct. 29, 2007 (JRS)

Auroras - Mon. Oct. 29, 2007 (JRS)

I’ve been meaning to post a blog (and more importantly, pictures) about auroras for some time now, but just haven’t gotten around to it.  I’ll put all of the pictures in our picture gallery, which can be found here: South South Pole April Auroras, South Pole May Auroras, South Pole June Auroras, South Pole July Auroras, and South Pole August Auroras

Here is some information about auroras, for those who are curious (thanks to Robert Schwarz, who gave a presentation about auroras at the beginning of the winter).

In the southern hemisphere, they’re called aurora australis (as opposed to aurora borealis in the North).  Basically, auroras are caused by charged particles that are emitted by the sun (referred to as the solar wind) interacting with the Earth’s atmosphere.  I won’t go into what causes the solar emissions, but I will say that solar emission cycle lasts about 11 years, during which the average solar activity experiences a maximum, decreases to a minimum, then increases back to a maximum.  So, some years are better than others for aurora viewing.  This past winter was a couple of years after the solar minimum, so kind of towards the middle of the scale.  On top of this average activity, magnetic storms on the sun, caused by sun spots, will cause much more aurora activity.  When the sun emits a huge flare (a coronal mass ejection, or CME), you can expect a major aurora event a couple of days later.  Solar storms are hard to predict, but some websites (spaceweather.com, for example) track the solar activity, and generally give a heads up of a couple of days for particularly good auroras.

The charged particles from the solar wind follow the Earth’s magnetic field lines into the polar regions, which is why they are only visible in the upper latitudes.  The magnetic field lines run in more-or-less of a circle from the South Pole, out into space, and back into the North Pole.  They intersect the atmosphere somewhat away from the geomagnetic poles, which forms an auroral oval around the geomagnetic poles.  These are not quite circles and not quite centered on the geomagnetic poles because of the interaction with the solar wind, but if you imagine a circle around the geomagnetic poles, it’s fairly close to what the auroral oval looks like.  Note that there’s a distinct difference between the geomagnetic pole (which is located near the coast of Antarctica in the South) and the rotational pole (which is where we are).  If we were located at the geomagnetic pole, we’d actually see very few auroras, but the rotational pole turns out to be an excellent place for auroras because it’s in the heart of the auroral oval.  Another interesting fact is that because of the symmytry of the Earth’s magnetic field, the aurora seen in the South is more-or-less of a mirror image of the ones seen in the North (except for small variations caused by differences in atmospheric conditions).

There are many, many more details that I could go in to, but I won’t.  Suffice it to say that the most common color for auroras is green.  They can also be red or blueish-purple, which is spectacular to see, but harder to see with the naked eye (they turn out great on long-exposure pictures).  They also come in lots of different shapes and sizes due phenomenon in the atmosphere and magnetosphere.  But, I’ll stop here and let you head over to the picture gallery to enjoy some of my favorite shots from the winter: http://www.stauchy.net/gallery Or, see the top of this post for specific gallery links

-JRS

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