Date: Thu Aug 19 03:06:32 1999
Posted By: Ricky J. Sethi, PhD
Area of science: Astronomy
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
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 email@example.com.
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