The Sun and Auroras

Thanks to Dr. Eades and Twitter, I found out about a really neat iPhone app this morning. It's called 3D Sun and was written by an astrophysicist in collaboration with NASA scientists. It brings realtime satellite videos of the sun to your iPhone. Your phone will even notify you when a significant event is happening. If you don't have an iPhone, you can still see the same images on the web at the STEREO (Solar-Terrestrial Relations Observatory) website. (The sun looks green because the satellites are taking images in the extreme ultraviolet range.)

Watching the sun and perhaps catching a solar flare while it is happening would be exciting enough, but the app also offers links to other great stuff including images of the auroras as well as movies of previous flares. One fascinating movie shows a comet getting eaten up by the sun.

Apparently we are having some pretty spectacular auroras right now. The sun's activity, manifested in many ways including sunspots, is picking up again after being at its cyclical minimum. Auroras are caused by the geomagnetic storms that this solar activity originates in the atmosphere of our own Earth due to the solar wind. (You can see a movie of a comet's tail waving in the solar wind here.)

The northern (or southern) lights, as auroras are sometimes called, are caused by the excitation of electrons in the upper atmosphere. The colors come from the kind of atom or molecule that gets an electron or has an electron drop to a lower energy state. Oxygen atoms emit a green or brownish-red photon depending on the amount of energy absorbed. Nitrogen atoms emit a blue photon if they gain an electron and red if they are returning to the ground state after being in an excited state. The auroras form shapes because the electrons move along the magnetic field lines. (This is an extreme over-simplification.) When the disturbances are great, the lights can be seen as far south as the southern US and more temperate parts of Europe. For more information on auroras and how they are formed click here. For more on shapes, click here.

I have never seen the aurora. Someday I hope to. I think it would be well worth braving the freezing temps to view something as spectacular as this photo taken by Marketa Stanczykova in Iceland just a few days ago on February 16.