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Fantastic Northern Lights! A rare red aurora last night.
The aurora in Arkansas, USA
Photo copyrighted by Brian Emfinger
Permission to use has been granted.Last night we were out running errands around 6:15 and I commented to my husband that the sunset looked unusual. It was a brilliant orange in the west, but only over a fairly small area, didn't seem big enough to light up the whole sky. But, in the east, the clouds were an unusual pink color. Unfortunately, though I had my camera in the car, I didn't take a shot because there wasn't a "perfect" setting (the Champaign airport is not the prettiest foreground for such a shot), and so other than my comment, I have no record of this event that turns out to probably have been the first aurora that I've seen!
I was therefore surprised to get up this morning and read about the magnificent aurora that filled the sky around that time! The aurora was caused by a coronal mass ejection (CME) two days earlier. It can be viewed here http://www.spaceweather.com/images2011/22oct11/cme_c2_strip.gif.
More discussion about this event can be found on spaceweather.com, which also has a great collection of pictures from places as far south as New Mexico. The aurora was one of the fairly rare "red" ones.
Auroras are produced when electrons and protons from a CME interacts with the earth's magnetic field, generating electrical power. The discharge can be though of as a great big neon sign in the sky. Gases give off photons, light, when subjected to an electric field. Green auroras with a reddish lower border are fairly common, and originate at an altitude of about 60 miles above the earth. Red auroras are much rarer, and occur much higher in the atmosphere, 180 to 300 miles. They are associated with a large influx of electrons that move too slowly to penetrate deep into the atmosphere. At this altitude, the electrons lose their energy to oxygen atoms. The light produced is at a wavelength of 6300 and 6364 Angstroms on the spectrum, a true red color. Details of the process are still a mystery.
Here's a post that I did a year ago on solar flares and Newt Gingrich.