Blue aurora

At http://spaceweather.com … on March 3rd, had a piece on aurora, sparked by a prominent earth facing sun spot. Aurora are usually green, and sometimes red. These are the colours produced by oxygen when it is excited by electrons raining down from space. On February 22nd, a viewer in Norway, Micha Boumi, witnessed a blue aurora. 'All of a sudden the sky exploded and the sky looked like a great flame' he said. Blue is a sign of nitrogen – energetic particles striking ionised molecules of nitrogen at high altitude produces a cold azure glow. However, why in this instance the blue colour overwhelmed the green and the red on that day is not known.