[apaulo (Paul)]

Hi Silv

Yes an interesting question Silv! As we know the human eye can only see colour within an certain range of wavelength. I have witnessed three rather strong auroras and I certainly saw an brilliant red with one of them.
As for last night there maybe an easy answer. Remember the difference between an emission and reflection nebula? Both regions have excited Hydrogen atoms and the photon release is caused by the electron shifting from its N3 or N2 orbit down to its natural N1 state...releasing a photon as a result. The red we see in the Emission nebula is that actual photon release, but with a reflection nebula they are emission nebulas too but the light is scattered by dust, interstellar medium at el and the wavelength of blue is seen.
Now considering the aurora I think the red and green emission maybe scatttered as well to the naked eye..Certainly there was alot of cloud mositure and the like.
Some other friends of mine imaged lasts night's aurora too and captured a yellow into green into red aurora, but the yellow and green was on the horizon not high above 10 degrees.
As we know different atoms release different colours H,Na and 02 when the electrons move down from their exited state. Maybe the solar flare needs to be up to a certain strength for the aurora to express colours visually?

Regards Paul.