The Land of Aurora Borealis

It was an All-Asian night at the Aurora Borealis Lodge: just me, two visitors from Los Angeles, two from San Francisco, and our affable host Mok & his family.  The Lodge is 20 miles north of Fairbanks, on Cleary Summit (elevation 2000 ft), on a hill overlooking a beautiful forest, with a spacious viewing deck facing northward.  When we arrived at 10:30 pm, the sky was already glimmering with faint patches of aurora radiating modestly.  Over the course of the next 3-1/2 hours, we experienced an astounding display of auroral forms.  I've seen photographs of the northern lights, but still images can't convey the amazing dynamic nature of the phenomenon.  The greenish-white light morphed from a swirling plume to a billowing tower to a glowing arc across the sky, then back to faint patches with tiny delicate rays.  The light appeared white when viewed with the naked eye, but it took on a phosphorescent greenish hue when photographed at high shutter speed with a 10-second exposure.  My low-tech camera couldn't capture the images properly; I was envious of the overnight guests from Japan who had scurried out from their accommodations armed with tripods and SLR cameras with wide-angle lenses.  Here's a series of aurora borealis video clips that I cribbed from the University of Alaska museum:

The aurora borealis is best viewed on clear nights with minimal moonlight when the level of geomagnetic activity is elevated.  Activity is measured by the Kp index which ranges from 0 (no activity) to 9 (extremely high activity).  The greater your latitude, the less geomagnetic activity is required for the aurora to be visible.  The optimal location to view the aurora borealis is within the circumferential band that extends from 60 degrees to 70 degrees magnetic latitude, known as the auroral oval:

When the level of geomagnetic activity increases, the auroral oval starts extending southward, and the northern lights become visible at latitudes below 60 degrees.  There are entire websites dedicated to predicting when auroral activity reaches levels high enough to be seen.   Fairbanks, at the magnetic latitude of 64 degrees, only requires a Kp index of 1 for aurora-watching.  Seattle, at the magnetic latitude of 52.7 degrees, would need a Kp index of 7.  And Mexico City, at the magnetic latitude of 29.1, would need a Kp index of 9+++++++++