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Duration:03:29
Uploaded:2014-06-17
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SciShow tackles a Quick Question with a longish answer: What causes auroras? TL;DR: It's a breathtaking display of particle physics in action.
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Sources:
http://science.howstuffworks.com/nature/climate-weather/atmospheric/aurora2.htm
http://curious.astro.cornell.edu/question.php?number=780
http://pwg.gsfc.nasa.gov/polar/telecons/archive/PR_E-PO/Aurora_flyer/aurora-flyer_p2.doc.pdf
http://imagine.gsfc.nasa.gov/docs/teachers/lessons/xray_spectra/background-atoms.html
http://science.nasa.gov/science-news/science-at-nasa/2003/29dec_magneticfield/
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magearth.html
http://www.wikipremed.com/mcat_course.php?code=0104030101000000
http://nmp.jpl.nasa.gov/st5/SCIENCE/magnetosphere2.html
http://sciencefocus.com/qa/what%E2%80%99s-furthest-south-northern-lights-have-been-seen
(Intro)

If you've ever been lucky enough to see Auroras, you're very lucky and I'm very jealous because I never have but I do get some joy from understanding exactly what those dazzling ripples of color are.

You might have heard that they are caused by solar winds hitting our upper atmosphere.  That's one of those hand wavy answers that doesn't actually answer anything.  Cause like, What's a solar wind? Why do they exist? Why does it cause crazy space colors when it hits the atmosphere? And why do they mainly happen near the poles, except during some kind of major solar event?

The reason we don't talk about the real answer is because it is complicated and it involves a lot of physics.  Answers do that a lot around here.

Before we can understand auroras we have to understand a little bit about the earths magnetic field.  In a lot of ways it is just like the magnetic field you get around a typical classroom bar magnet, the lines of the magnetic field flow of the top of one pole, loop down and flow into the other.   These looping magnetic field lines create a shield around the earth that extends into space about 64,000Km.  And it is shaped kind of like a doughnut with small holes at the top and bottom.  That doughnut is the only thing keeping out atmosphere from getting stripped away by 28,000 degrees solar plasma.

And make no mistake, people say solar wind which makes it sound all pleasant and breezy but it's plasma, high energy, high speed super hot particles that are byproducts of the fusion that is happening inside the sun.

And that wind packs quite a punch.  It actually distorts the shape of our magnetic doughnut, squashing it on the side facing the sun and blowing it out into a long tail on the other side.  But although out doughnut bends it does not break, so those super hot, super fast particles get deflected by our magnetic field and instead of smacking us straight in the teeth, they flow along the field lines toward the north and south poles, and they hit our atmosphere around the holes of the doughnut. 

So wherever those holes are, that's where you see auroras because that's where the charged particles are actually hitting the earth.

Now from time to time the sun breaks huge wind, if you know what I mean, releasing giant plumes of particles.  The stronger the solar wind gets, the more our magnetic doughnut gets distorted and the bigger its holes become.

During the great solar storm of 1859 for instance, the Northern Lights were seen as far south as Honolulu.  At that point we had more hole than doughnut.  

But, that doesn't explain anything about the pretty colors.

Our atmosphere is 99% nitrogen and oxygen and when those atoms are struck by those particles.  That energy puts the atoms into an excited state.  An atom is excited when it receives enough energy for its electrons to jump around into higher orbits around its nucleus.  But while this condition is exciting, it is not stable so the atmosphere quickly relax back into their ground state and release the energy they absorbed from the impact in the form of photons. Those photons are little packets of light, are the auroras that you see.

The colors vary depending on what kind of gas there is in the atmosphere at a particular place and time.  Oxygen atoms release photons at longer wavelengths, making green, yellow or red light.  Nitrogen atoms meanwhile release high-frequency blue light, the result is a breathtaking display of particle physics in action.

So the question may be a quick one but the answer isn't exactly.

Thanks for asking and for watching and thank you especially to our Subbable subscribers who keep our professional question answerers employed.  

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