Northern Lights are usually green, and sometimes red. Those are the colors produced by oxygen when it is excited by electrons raining down from space. On Feb. 22nd, Micha Bäuml of Straumfjord, Norway, witnessed an appariton of aurora-blue:
"All of a sudden the sky exploded," says Micha. "The aurora looked like a giant flame."
In auroras, blue is a sign of nitrogen. Energetic particles striking ionized molecular nitrogen (N2+) at very high altitudes produces a cold azure glow of the type captured in Micha's photo. Why it overwhelmed the usual hues of oxygen on Feb 22nd is unknown. Auroras still have the capacity to surprise.
Any auroras tonight, blue or otherwise, will be a bit of a surprise. Geomagnetic conditions are quiet. NOAA forecasters estimate a scant 5% chance of polar geomagnetic storms on March 3rd. - Space Weather.