We didn't expect to see much in the way of auroral activity until we left the bright skies of Fairbanks, for the dark skies of Chena Hot Springs Resort on 12 March. But Barnaby and Anne Finch, who were staying a little ways out of town at another B&B, invited us out to come out for a taste of things to come. By the time we found the place, the aurora was in full swing, with prominent "curtains" low in the southeast. It was a strong, if not very dynamic display.
For photography, I used mainly my 35mm Canon EOS SLR camera with a 24mm wide-angle lens all the way open at f/2.8. I used Fuji Superia 800 ASA film and various exposure times ranging from 10 to 30 seconds. I got through 8 rolls of 24 exposure film in total, and am only showing the best ones here, which have been digitally scanned from the original negatives. While film doesn't capture the dynamic nature of an aurora, what it does do is bring out the full range of colours. To the eye, the displays shown here looked to have a pale green hue. For night vision, we rely more on the "rods" rather than the "cones" in our retinas to see better, but this is at the expense of colour sensitivity. Thus, we tend to miss the deep greens, reds, and purples that show up better in photographs.
What causes these colours? It all depends on the types of atoms and molecules being stimulated, and the energy of the particles hitting them. The green is due to oxygen atoms at about 100 km altitude, while the deep red colour comes from oxygen at about 300 km. Ionised nitrogen molecules produce a blue glow, while neutral nitrogen molecules give rise to purplish-red borders and ripples.
On to Night 2...