August 6, 2011 – The Amazing Sky

Here is nearly two hours of auroral dancing compressed into 25 seconds.

This was the “all-sky” aurora of August 5/6, 2011, widely seen over North America but perhaps (from early reports) best from the western half, especially Canada, favoured for Northern Lights due to our latitude.

I shot this with the 8mm fish-eye lens and the Canon 5D MkII. The movie consists of 255 frames, each 24 to 30 seconds in exposure duration, taken one second apart. ISO speed was 1600 and aperture f/3.5. The playback frame rate is 10 fps.

This display was quite chaotic, without the graceful rippling curtains present in many displays, but rather huge patches of sky turning off and on. This is typical of an aurora in the declining part of the storm — it had already been raging for several hours by the time it got dark here in Alberta.

Nor was the display very bright, so the longer exposures needed to record it well further blur any fine motion. Nevertheless, you get a good idea of the intense activity this aurora displayed. The magnetosphere was jumping last night!

It’s been quite a while since I’ve seen a display of Northern Lights as good as this one. But with the Sun picking up in activity from a record lull in the last few years, great all-sky displays like this might become more frequent.

The last time I saw aurora cover most of the sky like it did last night (August 5) was back in the days of shooting film. So this was the first chance I had to shoot an all-sky aurora with digital cameras. This is with the Canon 7D and the ultra-wide 10-22mm zoom. I also shot with the fish-eye 8mm, and an “all-sky” movie of those frames will be in the next posting.

This display was widely seen and predicted, as solar monitoring satellites had observed major flares on the Sun earlier in the week and tracked the resulting “coronal mass ejections” across the solar system. We knew they were aimed at Earth and would hit August 5. In this case, the resulting geomagnetic storm raged for long enough that people across a wide swath of longitudes from Europe to North America were able to see the display during their local night, August 5/6. Even people in the northern U.S. had a good look.

While the display was certainly active and extensive it never did get really bright. So this one still falls short of the “10 out 10” scale for spectacle. Nevertheless, as digital cameras can do so well, the images picked up the greens from glowing oxygen with remarkable intensity. More interesting are the purples, seen toward the beginning of the night but then they faded away. The purple tints come from the tops of the towering curtains of aurora which often glow red from nitrogen molecules at very high altitudes being charged up and excited. But the tops of the curtains can also be lit by sunlight. The blue from the sunlight and the red from the aurora itself mix to produce a purple tint. Only the camera picked this up.