What are the Northern Lights? What causes the shapes to pulsate and change color / appearance? Are there Southern Lights?
High energy particles from the sun funneled down into the atmosphere due to Earth’s magnetic field. The energetic collision of these particles with the atoms of Earth’s atmosphere emits visible light. I’m sure someone else here could explain this in more detail. Yes, I think there are Southern Lights too.
Welcome, Bocephus! Good to have you with us here on the Straight Dope Message Board.
As Phobos stated, the Northern Lights, or aurora borealis, is merely solar radiation striking the Earth’s atmosphere as it passes by. Given the strength of the magnetic field in the polar regions and the energy of the solar radiation as it hits the atmosphere, you get the atoms of atmospheric gases into a very excited state where they give off energy and bounce around.
This page seems to be a good source of information on the Northern Lights.
Of course the same thing applies to aurora australis, also known as the Southern Lights.
Having said that, allow me to direct your attention both to the Search engine here on the Message Board and the Archives search engine on the front page. Using either of those will almost certainly direct you to any existing threads (or columns by Cecil Adams) on the particular subject of interest. It seems, however, that the Archive search engine is acting a tad buggy so stick with the Message search engine for now.
Judging from your description of them in the OP, am I to assume that you’ve seen them recently? If so, consider all of us jealous.
Further details: Those particles thrown off from the Sun are typically from solar magnetic storms, which are more common this year because we’re at the peak of the eleven-year solar cycle-- you’ll also see more sunspots than usual right now, too. We can see storms occuring instantly (well, almost-- there’s still the 8-minute lag for ligh), but the particles typically take 2-3 days to get here, so we can get about that much warning on when aurorae are likely to occur.
The reason the aurorae only occur at the poles is the shape of the Earth’s magnetic field. The field has it’s poles near the polar regions of the Earth, though they aren’t precisely lined up. The axis of the planet’s spin is not the same as the ends of the Earth’s internal magnet.
When charged particles impinge on the Earth, the magnetic field causes their paths to curve. Many of them end up in orbit in a couple of regions known as the Van Allen radiation belts. If the particle comes in at an angle, it may not orbit, and instead will follow the magnetic field lines down to the planet, striking the atmosphere close to the poles.
In years of increased solar activity, enough particles hit to spread out the impact zone. So the lights are sometimes visible further toward the equator than in other years.
It’s pretty tough to see them at this time of year, as the sky is still not dark until after midnight. Oh yeah, I’m north of 60° Latitude. Winter time is much better viewing.
They are pretty cool to see, but IRL they are a lot more faint than you see in photographs and such. Usually you have to be looking for them.
Usually I’ll just be driving along or something, and notice what looks like a thin and wispy cloud in the sky, illuminated by the lights at a mall or car dealer’s parking lot. Then a few moments later, I realize that no car dealers or shopping malls are in that direction, and it is the Northern Lights.
Incidentally, the Japanese believe there is nothing luckier than to be conceived under the Aurora Borealis. And I’m slowly maneuvering to build a Bed and Breakfast style resort on my little ranch to accommodate their conceptual attempts under the glowing skies.
Recent sunspot activity has produced some pretty good aurora activity. A few weeks ago, sightings were reported in Virginia. This site or this will give you a heads up.
honkytonkwillie, I spent the winter of '88 in Juneau AK and the Lights that year were INCREDIBLE. Not faint at all, quick moving and very flashy. I also remember them forming complete rings and expanding outward instead of loking like streamers snaking across the sky - made me wonder if I was watching the action occurring right around the North Magnetic Pole.
Any astronomers able to clear that one up for me?
Question first and then you can read my story of you’re so inclined…
Why is the earth’s magnetic field not lined up with the poles? Is the field perpendicular to the earth’s orbit or something?
Now for the story…
Ok…so maybe saving my marriage is a gross overstatement. My wife and I had a minor argument over something or other while on vacation up near Jasper in Alberta, Canada. She went to sleep and I stood on our balcony feeling sorry for myself when I noticed lights coming from behind a hill. I figured some locals were parked near the ridge with their headlights on till I realized that those ‘hills’ were mountains (I’m from Illinois and it’s terribly flat here). If there were trucks doing that there’d need to be thousands of them. It slowly dawned on me that I was seeing the Northern Lights. Excited I called for my wife to come look and she told me where I could shine those lights. Not to be put off I persisted and she finally came out. Once she saw them we both promptly forgot whatever stupidness we had been fighting about and enjoyed the 30 or so minute light show.
The ones I saw were nowhere near as exciting as in the pictures being mostly green but they were pretty vivid (fading in and out). I asked the hotel receptionist (who presumably lived around there) about them the next morning and she was jealous because SHE had never seen them in her life! That’s what you get from watching too much MTV instead of finding some of life’s other joys!
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*Originally posted by Jeff_42 *
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We don’t know why it’s not lined up with the poles, but we do know that it ain’t, so presumably it doesn’t have to be. It is not aligned with anything else, so far as we know–in fact, it occasionally reverses itself
Not an astronomer, but aurora doesn’t occur directly over the geomagnetic pole. It occurs in an oval around it. If the sun shoots out more particles, the oval expands. This was more likely at that time because 1988 was the start of the active period of the previous 11-year sunspot cycle. You may have been right under the expanded auroral oval some of the time - very lucky! 
More aurora info:
NOAA aurora viewing tips
Sky and Telescope – AstroAlert News Service
Solar Terrestrial Dispatch Homepage