MadSci Network: Astronomy

Re: Are Aurorae Australis a reflection of the Aurorae Borealis?

Date: Thu Aug 19 03:06:32 1999
Posted By: Ricky J. Sethi, PhD
Area of science: Astronomy
ID: 933797876.As

Hi Zoe,


You're exactly right... the aurorae are, indeed, caused by the interaction of particles thrown out from the Sun with the Earth's atmosphere. Instead of going into the cause of the light show itself, I'll concentrate specifically on the "mirror images" aspect. If you'd like a little refresher on the physics of the aurora, please check this previous MadSci Answer by Phil Plait. Okay, on to the question at hand...


Although you were right in surmising the cause of the light show, the exhibit was also correct! What happens is that particles from the Sun (i.e., electrons and protons) are constantly being blown towards the Earth. This is the so-called solar wind. These electrically charged particles are affected by the magnetic field of the Earth and spiral down along the field lines towards the poles. When they hit the atmosphere, you get an aurora.

Now, the Earth's magnetosphere (please see above picture), like any other magnet, has two poles, a North and a South pole. So this solar wind, made up of charged particles, splits up and travels down the field lines toward locations where the field is the strongest: each of the poles. Thus, we have two aurorae, the Aurora Borealis and it's conjugate aurora, the Aurora Australis (please see picture below).

Because the magetic field is three dimensional, it intersects the atmosphere in a circle. Thus, when the solar wind particles follow the magnetic field lines down to the upper atmosphere (interestingly, the particles don't follow the field lines straight down; rather, they spiral down the field lines), they also form a circular ring when they interact with the atoms in the Earth's atmosphere. Thus, two rings are formed, one at each pole. And that's why the aurorae are called "reflections" of each other (please see the pictures below).


Well, I hope that explanation made sense... if not, you might want to check out the following links about this fascinating and beautiful phenomenon (btw, if you do go to these sites, please be sure to see some of the incredible pictures they exhibit; in fact, I pilfered all the above pictures from these very links :). And if you have any further questions whatsoever, please feel free to drop me a line at



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