Star Trails and Northern Lights

I went out last night in search of the northern lights again.  The forecast numbers were looking good but by the time I got on location the lights were very faint.  I decided to try a star trail exposure while waiting to see if the lights would pick up.  I let the exposure run for 72 minutes and during that time the glow of the northern lights didn't seem to change.  It was an almost imperceptible glow that showed up quite nicely on the one hour and 12 minute exposure.  As always, it was an amazing night to be out under the stars!